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LINICAL RESEARCH STUDY

he Association between Smoking and Low Back Pain:Meta-analysis

ahman Shiri, MD, PhD,a Jaro Karppinen, MD, PhD,a,b Päivi Leino-Arjas, MD, PhD,a Svetlana Solovieva, PhD,a

ira Viikari-Juntura, MD, PhDa

Centre of Expertise for Health and Work Ability, Finnish Institute of Occupational Health, Helsinki, Finland; bDepartment of Physical

edicine and Rehabilitation, University of Oulu, Oulu, Finland.

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E-mail address

002-9343/$ -see foi:10.1016/j.amjm

ABSTRACT

BJECTIVE: To assess the association between smoking and low back pain with meta-analysis.ETHODS: We conducted a systematic search of the MEDLINE and EMBASE databases until February009. Eighty-one studies were reviewed and 40 (27 cross-sectional and 13 cohort) studies were includedn the meta-analyses.ESULTS: In cross-sectional studies, current smoking was associated with increased prevalence of low backain in the past month (pooled odds ratio [OR] 1.30, 95% confidence interval [CI], 1.16-1.45), low backain in the past 12 months (OR 1.33, 95% CI, 1.26-1.41), seeking care for low back pain (OR 1.49, 95%I, 1.38-1.60), chronic low back pain (OR 1.79, 95% CI, 1.27-2.50) and disabling low back pain (OR 2.14,5% CI, 1.11-4.13). Former smokers had a higher prevalence of low back pain compared with nevermokers, but a lower prevalence of low back pain than current smokers. In cohort studies, both former (OR.32, 95% CI, 0.99-1.77) and current (OR 1.31, 95% CI, 1.11-1.55) smokers had an increased incidencef low back pain compared with never smokers. The association between current smoking and thencidence of low back pain was stronger in adolescents (OR 1.82, 95% CI, 1.42-2.33) than in adults (OR.16, 95% CI, 1.02-1.32).ONCLUSIONS: Our findings indicate that both current and former smokers have a higher prevalence andncidence of low back pain than never smokers, but the association is fairly modest. The associationetween current smoking and the incidence of low back pain is stronger in adolescents than in adults.

2010 Elsevier Inc. All rights reserved. • The American Journal of Medicine (2010) 123, 87.e7-87.e35

KEYWORDS: Incidence; Prevalence; Publication bias; Tobacco

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ow back pain is a worldwide health problem, affectingetween 50% and 80% of people at some time in theirives.1,2 Its annual prevalence in the general populations

Funding: None.Conflict of Interest: The authors declare that they have no competing

nterests.Authorship: All authors had a role in writing the manuscript. All

uthors contributed to the design of the review, as well as interpretation ofhe findings and preparing the report. R. Shiri and S. Solovieva carried outhe MEDLINE searches. R. Shiri carried out the EMBASE searches. Alluthors assessed the quality of the studies. R. Shiri carried out the meta-nalyses and drafted the manuscript. All authors critically revised theanuscript and approved the final version for submission.

Requests for reprints should be addressed to Rahman Shiri, MD, PhD,entre of Expertise for Health and Work Ability, Finnish Institute ofccupational Health, Topeliuksenkatu 41 a A, Helsinki FIN-00250, Fin-

and.

O: rahman.shiri@ttl.fi

ront matter © 2010 Elsevier Inc. All rights reserved.ed.2009.05.028

anges between 25% and 60%, and the 1-month prevalences around 30%.1,2 Low back pain is associated with reduceduality of life, sickness absence, loss of worker productiv-ty, and high health care costs.2-5

The etiology of low back pain is not fully known. Studiesuggest that modifiable risk factors may play a role in theevelopment of low back pain.6,7 However, the availablevidence on the role of smoking in low back pain is incon-istent.8 To date, 2 reviews on the association betweenmoking and low back pain have been published.8,9 One ofhese suggested an association between cigarette smokingnd low back pain,9 while the other reported unclearndings.8

These 2 reviews on the relation between smoking andow back pain covered studies published between 1974 andid-1997. Moreover, no meta-analysis has been performed.

ur aim was to provide a systematic literature review of the

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87.e8 The American Journal of Medicine, Vol 123, No 1, January 2010

ssociation between smoking and low back pain and tostimate the magnitude of such an association witheta-analysis.

ETHODS

earch Strategytudies of interest were identifiedy searches of the MEDLINE andMBASE databases from 1966ntil February 2009 using pre-efined keywords. In addition tomoking, our search covered aarger set of cardiovascular or life-tyle risk factors.10,11 Our searchas limited to human populations.ll languages were accepted. We

xcluded reviews, case reports,etters, editorials, and guidelines.

e also searched reference lists ofncluded studies.

election of Studieswo authors examined independently all titles and ab-tracts. We scrutinized the full text of relevant articles andetermined whether they met the inclusion criteria. Wencluded original articles on human populations with a co-ort, case-control, or cross-sectional design. Studies solelyn clinical populations, case-control studies with controlserived from the patient populations, studies with sampleize �30, and studies with response rate �60% or noteported, were excluded (Figure 1). Studies on specific backisorders,11 on musculoskeletal or spinal pain without spec-fication to the back, and studies on the prognosis of lowack pain were excluded.

uality Assessmentwo reviewers assessed independently the quality of thetudies using a modification of the Cochrane quality criteriaor the systematic assessment of nonexperimental studies.12

isagreements were solved through discussion.We assessed the occurrence and severity of 4 possible

ources of bias: selection, performance, detection, and at-rition (Appendix 1). Studies with any definite biases werexcluded from the review. Only studies with no or minorelection bias were included in the meta-analysis.

eta-analysistudies that reported a risk estimate (odds ratio or relativeisk) for smoking were eligible for the meta-analysis. Ainimum requirement was adjustment for age and sex.hen the study population was of either sex, represented a

arrow age group, or included stratified analysis by age andex, the study also was included.

We used combinable low back pain outcomes suggested

CLINICAL SIGNIF

● Smoking might iback pain.

● Smoking mighteffects on the lucents than adult

● Smoking cessatirisk of seekingand chronic low

y the Meta-Analysis of Pain in the Lower Back and Work s

xposures collaborative group.13 Chronic low back painas defined as pain that lasts for longer than 7-12 weeks2 orain for more than 30 days in the past 12 months.13

We did random-effects meta-analyses. Results from aandom-effects model are usually more conservative than

the fixed-effect model.12 Hetero-geneity was assessed by the Coch-ran’s chi-squared (Q-test) and I2

statistic.14,15 Heterogeneity refersto any kind of variability in the as-sociation between smoking and lowback pain among different studies.Significant heterogeneity shows thatthis variability is not due to chancealone. Values of I2 statistic rangefrom 0% to 100% and show theproportion of total variation acrossstudies that are not due to chance.Values of 25%, 50%, and 75% cor-respond to low, moderate, and highheterogeneity.15

The small-study effect and the effect of low-quality stud-es were assessed by cumulative meta-analysis and by sub-roup analysis. For cumulative meta-analysis, the studiesere ranked in descending order, first by number of mod-

rate biases and then by sample size. Meta-regression wassed to determine whether study-level covariates accountor the observed heterogeneity.16

Publication bias was examined with funnel plots. A fun-el plot is a scatter plot of included studies in the meta-nalysis, with the magnitude of smoking effect on the hor-zontal axis, and the weight of the study, such as the inversetandard error or sample size, on the vertical axis. Theunnel plot is based on the fact that the precision in assess-ng the association between smoking and low back pain willncrease as the sample size of studies increases. An asym-etrical appearance of dots in the funnel plot can be due to

he presence of publication bias.17 Asymmetry of funnellots was assessed by 3 statistical methods: rank correlationethod (Begg’s test),18 regression analysis (Egger’s test),19

nd the trim-and-fill method.20 In the trim-and-fill method,e used the fixed-effect model for trimming and the ran-om-effects model for filling to obtain the adjusted pooledstimates. We assessed publication bias for cross-sectionalnd cohort studies as well as for each low back pain out-ome. Stata software, version 10 (StataCorp, College Sta-ion, Tex), was used to perform meta-analysis.

ESULTSe identified 250 relevant study reports on the associations

etween cardiovascular risk factors and low back pain foretailed assessment (Figure 1). We included 81 studies onhe relation between smoking and low back pain for sys-ematic review (Appendixes 2,3). Finally, 40 (27 cross-

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87.e9Shiri et al Association between Smoking and Low Back Pain

ross-sectional Studiesompared with those who never smoked, ever, former, andurrent smokers had a higher prevalence of low back pain inhe past month, in the past 12 months, seeking care for lowack pain, and chronic low back pain (Tables 1-3). Therevalence of low back pain in the past month did not differetween former and current smokers, whereas currentmokers had a higher prevalence of low back pain in theast 12 months, seeking care for low back pain, or chronicow back pain than former smokers (Tables 2,3). Currentmoking had the strongest association with disabling lowack pain.

Of 8 studies included in the meta-analysis on the asso-

Figure 1 Flow chart of the se

iation between current smoking and chronic low back pain, t

assessed a dose-response relation between the numberf cigarettes smoked per day and chronic low backain.30,31,40,42,54 Of them, 4 showed a dose-responseelation.30,40,42,54

ohort Studieshe meta-analysis of prospective studies showed an in-reased incidence of low back pain in ever, former, andurrent smokers compared with never smokers (Table 4).he association between current smoking and low back painas stronger in adolescents than in adults. All studies in

dolescents56-58 showed a dose-response relation betweenhe number of cigarettes smoked per week or per day and

rategy and selection of studies.

he incidence of low back pain.

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87.e10 The American Journal of Medicine, Vol 123, No 1, January 2010

No association was found between smoking and sicknessbsence due to low back disorder (Table 4).

ex-specific Analysesormer and current smoking was associated with increasedrevalence of low back pain in both sexes (Tables 5-7).ale former smokers had a higher incidence of low back

ain than never smokers. Male former smokers had a higherrevalence of chronic low back pain and higher incidence ofow back pain than female former smokers. No other sexifferences were observed.

ublication Biashe funnel plot of the cross-sectional studies on the asso-iation between ever (one study) or current (26 studies)moking and any low back pain was asymmetrical (Figure). The results suggest that some medium-sized and smalltudies with negative findings were not published. Bothegg’s (P � .070) and Egger’s (P � .009) tests showed ev-

dence of publication bias. The trim-and-fill method im-uted 8 missing studies.

The funnel plot of the cohort studies on the association

Table 1 Pooled Odds Ratio of Low Back Pain for Ever SmokersStudies)

irst Author Population Country YearSamSiz

ow back pain in the past monthSchneider22 General Germany 2005 6Nagasu26 Occupational Japan 2007 5Ghaffari24 Occupational Iran 2007 3Heistaro27 General Finland 1998 29Croft25 General UK 1994 9Leino-Arjas28 General Finland 1998 7

ooled 61ow back pain in the past 12 months

Pietri35 Occupational France 1992 1Skov33 Occupational Denmark 1996 1Wright34 General UK 1995 24

ooled 27djusted for publication biaseeking care for low back pain

Wright34 General UK 1995 24Leino-Arjas28 General Finland 1998 7

ooled 31hronic low back paindults

Leclerc41 General France 2008 15Björck-van Dijken43 General Sweden 2008 5Heliövaara40 General Finland 1991 5Silva39 General Brazil 2004 3Andersson42 General Sweden 1998 1

ooled 31djusted for publication biasdolescents

Hestbaek54 Twins Denmark 2006 9ooled (adults � adolescents) 35djusted for publication bias

OR � odds ratio; CI � confidence interval.

etween ever (1 study) or current (12 studies) smoking and a

he incidence of low back pain was symmetrical (Figure 2).egg’s test showed no evidence of publication bias

P � .16). However, Egger’s test showed an evidence of aossible publication bias (P � .079). No missing study wasmputed by the trim-and-fill method. When Egger’s test waspplied to 9 studies on 1-year incidence of low back pain,he test showed no publication bias (P � .26).

ensitivity Analysisdjusting for publication bias did not affect the associationetween current smoking and low back pain. It attenuatednly the pooled estimate of low back pain in the past monthTable 3). For ever smoking, adjustment attenuated theooled estimate of chronic low back pain and for formermoking, the estimates of low back pain in the past 12onths and chronic low back pain (Tables 1, 2).In cumulative meta-analyses the pooled estimates were

ot affected by the small or low-quality studies (Tables 1-4).In meta-regression, heterogeneity across studies on low

ack pain in the past month was not associated with thetudy population, publication year (before or after the year000), recall period of low back pain (1 to 4 weeks),

Never Smokers among Adults, Prevalence (Cross-sectional

OR 95% CI

Heterogeneity No. ofModerateBiases

Cumulative OR(95% CI)P Value I2 (95% CI)

1.25 1.14-1.37 0 1.25 (1.14-1.37)1.48 1.23-1.77 0 1.34 (1.13-1.57)1.18 0.95-1.47 0 1.29 (1.15-1.45)1.21 1.15-1.27 1 1.25 (1.16-1.33)1.35 1.22-1.49 1 1.27 (1.19-1.36)1.22 1.13-1.33 1 1.26 (1.19-1.32)1.26 1.19-1.32 .17 35 (0-74)

1.40 1.10-1.70 0 1.40 (1.10-1.70)1.40 1.12-1.74 0 1.40 (1.20-1.60)1.30 1.23-1.36 1 1.31 (1.25-1.37)1.31 1.25-1.37 .67 0 (0-90)1.30 1.24-1.36

1.35 1.26-1.44 11.24 1.10-1.39 11.31 1.21-1.42 .21

1.21 1.12-1.32 0 1.21 (1.12-1.32)1.29 1.11-1.49 0 1.23 (1.14-1.32)1.40 1.22-1.61 0 1.28 (1.17-1.40)2.07 1.43-3.00 0 1.35 (1.18-1.55)1.62 1.28-2.05 0 1.40 (1.22-1.60)1.40 1.22-1.60 .009 70 (24-88)1.29 1.12-1.48

1.77 1.44-2.17 01.47 1.27-1.69 .001 77 (48-90)1.42 1.23-1.63

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87.e11Shiri et al Association between Smoking and Low Back Pain

ent smokers, or the presence of moderate bias. The pooledstimate in occupational populations, however, was higherhan that for studies in general populations (odds ratio [OR].46 vs 1.34). There was only minor heterogeneity acrosstudies published after the year 2000 (I2 8%). Country andhe prevalence of low back pain were significant determi-ants of heterogeneity. The pooled estimate was lower ininland than in the other countries. The pooled OR was 1.5195% confidence interval [CI], 1.28-1.78; I2 53%) for stud-es with a prevalence of low back pain �30%, and 1.2695% CI, 1.14-1.39; I2 59%) for studies with a prevalence ofow back pain �30%.

Heterogeneity across studies on chronic low back painas not associated with publication year, the proportion of

urrent smokers, or the prevalence of low back pain. Studyopulation, country, and adjustment for potential confound-rs were determinants of heterogeneity. The pooled OR wasigher in Denmark (OR 2.34), in a twin population (OR.36), and in studies that did not control the obtained OR forhysical work load factors or psychosocial factors (OR.79). The pooled estimate was 1.43 (95% CI, 1.21-1.70) instudies in adults that controlled the obtained ORs for

hysical work load or psychosocial factors.For other low back pain outcomes, the pooled estimates

id not differ when the meta-analyses were restricted tohose studies that controlled the obtained ORs for commononfounders. For current smoking, the pooled estimate ofow back pain in the past month was 1.41 (95% CI, 1.23-

Table 2 Pooled Odds Ratios of Low Back Pain for Former SmokStudies)

irst Author Population Country Year Sa

ow back pain in the past monthSchneider22 General Germany 2005Nagasu26 Occupational Japan 2007Ghaffari24 Occupational Iran 2007Heistaro27 General Finland 1998 29Croft25 General UK 1994Leino-Arjas28 General Finland 1998

ooled 61ow back pain in the past 12 months

Skov33 Occupational Denmark 1996Wright34 General UK 1995 24

ooled 25djusted for publication biaseeking care for low back pain

Wright34 General UK 1995 24Leino-Arjas28 General Finland 1998

ooled 31hronic low back pain

Leclerc41 General France 2008 15Björck-van Dijken43 General Sweden 2008Heliövaara40 General Finland 1991Silva39 General Brazil 2004Andersson42 General Sweden 1998

ooled 31djusted for publication bias

OR � odds ratio; CI � confidence interval.

.63), low back pain in the past 12 months 1.31 (95% CI, l

.23-1.41), and the incidence of low back pain in adults 1.1895% CI, 1.02-1.36). All studies on the incidence of lowack pain in adolescents controlled the obtained risk esti-ates for potential confounders.

ISCUSSIONhis meta-analysis showed an association between smokingnd low back pain. The association was strongest forhronic low back pain and disabling low back pain. Formermokers were at a lower prevalence of low back pain thanurrent smokers. The association between smoking and thencidence of low back pain was stronger in adolescents thann adults.

The observed association between smoking and low backain was modest. The multifactorial etiology of low backain needs to be considered in the interpretation of thendings. Most causal factors of a multifactorial disease haverelatively weak effect.100 The slight sex difference in the

ssociation may be due to chance.Some studies have reported an association between

moking and low back pain only in people with heavyhysical work.45,62 People in physically demanding jobsay smoke more. Thus, physical exposures at work could

onfound the association between smoking and low backain. Smokers also have a poorer mental health status thanonsmokers.101 Therefore, smoking might be a surrogatearker of an underlying psychological problem that causes

rsus Never Smokers among Adults, Prevalence (Cross-sectional

OR 95% CI

Heterogeneity No. ofModerateBiases

Cumulative OR(95% CI)P Value I2 (95% CI)

1.25 1.09-1.44 0 1.25 (1.09-1.44)1.35 1.01-1.79 0 1.27 (1.12-1.44)0.70 0.40-1.20 0 1.18 (0.92.1.50)1.27 1.17-1.37 1 1.25 (1.12-1.39)1.33 1.16-1.53 1 1.27 (1.17-1.37)1.27 1.11-1.46 1 1.27 (1.20-1.35)1.27 1.20-1.35 .39 3 (0-75)

1.51 1.09-2.10 01.20 1.11-1.30 11.27 1.05-1.55 .181.20 1.00-1.44

1.14 1.03-1.26 11.11 0.91-1.36 11.13 1.03-1.24 .81

1.25 1.10-1.42 0 1.25 (1.10-1.42)1.26 1.05-1.52 0 1.25 (1.12-1.39)1.20 1.00-1.60 0 1.24 (1.13-1.37)1.64 0.88-3.05 0 1.25 (1.14-1.38)1.66 1.19-2.32 0 1.28 (1.16-1.40)1.28 1.16-1.40 .49 0 (0-79)1.24 1.11-1.38

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87.e12 The American Journal of Medicine, Vol 123, No 1, January 2010

nalysis, especially prospective studies, controlled for po-ential confounders. The results remained consistent wheneta-analyses were limited to the studies that controlled the

btained risk estimates for physical or psychosocial workoads. Therefore, our observed association between smok-ng and low back pain is unlikely due to workload factors orndividual psychological factors.

The temporal relationship is an essential aspect of cau-ality. For cigarette smoking to be a cause of low back pain,t has to precede low back pain onset. A causal associationetween smoking and low back pain cannot be establishedy randomized controlled trials due to ethical restraints.

Table 3 Pooled Odds Ratios of Low Back Pain for Current Smo(Cross-sectional Studies)

irst Author Population Country Year Sa

ow back pain in the past monthSchneider22 General Germany 2005Nagasu26 Occupational Japan 2007Ghaffari24 Occupational Iran 2007Heistaro27 General Finland 1998 2Croft25 General UK 1994Leino-Arjas28 General Finland 1998Brage23 General Norway 1996Miyamoto21 Occupational Japan 2008

ooled 6djusted for publication biasow back pain in the past 12 monthsdults

Leboeuf-Yde31 Twins Denmark 1998 2Leboeuf-Yde29,30 General Denmark 1997Skov33 Occupational Denmark 1996Strine7 General US 2007 2Wright34 General UK 1995 2Oksuz32 General Turkey 2006Karahan37 Occupational Turkey 2009Raanaas36 Occupational Norway 2008

ooled 9dolescents

Hestbaek54 Twins Denmark 2006ooled (adults � adolescents) 10eeking care for low back pain

Leino-Arjas28 General Finland 1998Wright34 General UK 1995 2

ooled 3hronic low back paindults

Leboeuf-Yde31 Twins Denmark 1998 2Leclerc41 General France 2008 1Björck-van Dijken43 General Sweden 2008Heliövaara40 General Finland 1991Silva39 General Brazil 2004Andersson42 General Sweden 1998Leboeuf-Yde29,30 General Denmark 1997

ooled 6dolescents

Hestbaek54 Twins Denmark 2006ooled (adults � adolescents) 7isabling low back pain

Harreby55 Children Denmark 1999Liira44 General Canada 1996 1

ooled (adults � adolescents) 2

OR � odds ratio; CI � confidence interval.

herefore, the most feasible study design for the assessment b

f causality in humans is the cohort study. We found anssociation between smoking and the incidence of low backain. The association was stronger in adolescents than indults. Adolescents might be more vulnerable than adults tohe adverse effects of smoking.102 They also have a lowerrevalence of low back pain, better enabling studies on truencidence of low back pain.

The reviewed studies had some major limitations. Theutcomes in many studies did not include information onhe frequency and severity of low back pain, and differentecall periods and case definitions were used. A limitedumber of prospective studies on the role of smoking in low

rsus Never Smokers among Adults and Adolescents, Prevalence

OR 95% CI

Heterogeneity No. ofModerateBiases

Cumulative OR(95% CI)P Value I2 (95% CI)

1.27 1.10-1.47 0 1.27 (1.10-1.47)1.57 1.24-1.98 0 1.38 (1.13-1.70)1.30 1.00-1.60 0 1.34 (1.19-1.52)1.16 1.09-1.24 1 1.27 (1.13-1.43)1.40 1.20-1.60 1 1.30 (1.17-1.45)1.26 1.12-1.42 1 1.28 (1.18-1.40)1.84 1.50-2.25 1 1.36 (1.21-1.52)1.65 1.07-2.53 1 1.37 (1.23-1.53)1.37 1.23-1.53 �.001 74 (47-87)1.30 1.16-1.45

1.40 1.30-1.60 0 1.40 (1.30-1.60)1.30 1.00-1.60 0 1.38 (1.26-1.52)1.31 0.98-1.76 0 1.38 (1.26-1.51)1.30 1.20-1.40 1 1.33 (1.25-1.41)1.37 1.28-1.45 1 1.35 (1.29-1.41)1.10 0.90-1.30 1 1.33 (1.26-1.40)1.52 1.19-1.95 1 1.34 (1.27-1.41)0.99 0.73-134 1 1.32 (1.24-1.40)1.32 1.24-1.40 .13 37 (0-72)

1.40 1.25-1.56 01.33 1.26-1.41 .16 32 (0.68)

1.39 1.18-1.63 11.51 1.39-1.63 11.49 1.38-1.60 .36

3.00 2.80-3.30 0 3.00 (2.70-3.30)1.19 1.06-1.32 0 1.89 (0.76-4.68)1.33 1.05-1.67 0 1.69 (0.84-3.37)1.47 1.25-1.72 0 1.63 (0.95-2.78)2.36 1.49-3.74 0 1.74 (1.08-2.80)1.58 1.13-2.20 0 1.71 (1.12-2.62)2.30 1.60-3.30 0 1.78 (1.21-2.62)1.78 1.21-2.62 �.001 97 (96-98)

1.82 1.49-2.22 01.79 1.27-2.50 �.001 97 (95-98)

3.03 2.14-4.30 01.55 1.20-2.00 12.14 1.11-4.13 .002

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87.e13Shiri et al Association between Smoking and Low Back Pain

etailed information on number of cigarettes smoked peray, meta-analysis of the dose-response relationship wasot feasible because different cut-points for number of cig-rettes were used.

There may be a publication bias in favor of positiveesults between smoking and low back pain. Publicationias arises when studies with a statistically significant pos-tive association are more likely to be reported or publishedhan studies with a negative or null association. Language ofublication also influences accessibility. Publication bias isore likely to affect small studies, which tend to show

Table 4 Pooled Odds Ratios of Low Back Pain for Ever, FormerAdolescents, Incidence (Cohort Studies)

irst Author Population Country Year

ver smokingLow back pain in the past 12 months

Andersen48 Occupational Denmark 2007Leino-Arjas47 Occupational Finland 2006Miranda49 Occupational Finland 2008Pietri35 Occupational France 1992

PooledSickness absence (�1 day)

Hemingway50 Occupational UK 1999Ghaffari24 Occupational Iran 2007Van den Heuvel51 Occupational Netherlands 2004

Pooledormer smoking

Low back pain in the past 12 monthsAndersen48 Occupational Denmark 2007Leino-Arjas47 Occupational Finland 2006Miranda49 Occupational Finland 2008

PooledSickness absence (�1 day)

Hemingway50 Occupational UK 1999Ghaffari24 Occupational Iran 2007Van den Heuvel51 Occupational Netherlands 2004

Pooledurrent smoking

Low back pain in the past 12 monthsAdults

Andersen48 Occupational Denmark 2007Leino-Arjas47 Occupational Finland 2006Power46 General UK 2001Miranda49 Occupational Finland 2008Eriksen45 General Norway 1999

PooledAdolescents

Mikkonen57 Adolescents Finland 2008Feldman6,56 Children Canada 2001Mustard58 Children Canada 2005

PooledPooled (adults � adolescents)Sickness absence (�1 day)

Hemingway50 Occupational UK 1999Ghaffari24 Occupational Iran 2007Van den Heuvel51 Occupational Netherlands 2004

PooledSickness absence (�7 days)

Hemingway50 Occupational UK 1999Tubach52 Occupational France 2002

Pooled

OR � odds ratio; CI � confidence interval.

arger risk estimates than larger studies. We adjusted the p

ooled estimates for publication bias using the trim-and-fillethod, which spuriously adjusts for publication bias when

he studies are heterogeneous.103,104 The pooled estimatesere attenuated after adjustment for publication bias mostly

n the studies with moderate to high heterogeneity, suggest-ng that the true positive association between smoking andow back pain was underestimated. Funnel plot asymmetryay be caused by a number of factors other than publication

ias.19 All statistical methods for assessment of publicationias are unable to distinguish publication bias from otherauses of funnel plot asymmetry.104 We found that the study

rrent Smokers versus Never Smokers among Adults and

eOR 95% CI

Heterogeneity No. ofModerateBiases

Cumulative OR(95% CI)P Value I2 (95% CI)

1.03 0.77-1.38 0 1.03 (0.77-1.38)1.59 1.14-2.23 0 1.27 (0.83-1.94)1.17 1.01-1.37 1 1.21 (0.99-1.48)1.30 0.80-2.10 1 1.21 (1.04-1.42)1.21 1.04-1.42 .26 24 (0-88)

1.08 0.94-1.24 0 1.08 (0.94-1.24)2.77 1.45-5.29 0 1.64 (0.65-4.10)0.77 0.46-1.28 1 1.25 (0.73-2.15)1.25 0.73-2.15 .008 80 (35-94)

1.06 0.71-1.59 0 1.06 (0.71-1.59)2.00 1.23-3.24 0 1.44 (0.77-2.67)1.24 1.02-1.52 1 1.32 (0.99-1.77)1.32 0.99-1.77 .12 52 (0-86)

1.09 0.91-1.31 00.90 0.10-7.40 00.73 0.33-1.58 11.07 0.89-1.27 .61 0 (0-90)

1.00 0.70-1.40 0 1.00 (0.70-1.40)1.29 0.80-2.05 0 1.09 (0.83-1.45)1.25 1.03-1.51 1 1.20 (1.02-1.40)1.08 0.85-1.38 1 1.16 (1.02-1.33)1.11 0.68-1.82 1 1.16 (1.02-1.32)1.16 1.02-1.32 .76 0 (0-79)

1.60 1.02-2.53 0 1.60 (1.02-2.53)2.20 1.38-3.50 0 1.87 (1.35-2.59)1.75 1.19-2.57 2 1.82 (1.42-2.33)1.82 1.42-2.33 .61 0 (0-90)1.31 1.11-1.55 .075 46 (0-76)

1.07 0.87-1.31 0 1.07 (0.87-1.31)3.10 1.60-6.20 0 1.73 (0.61-4.89)0.80 0.41-1.57 1 1.34 (0.70-2.59)1.34 0.70-2.59 .007 80 (35-94)

1.20 0.81-1.78 02.04 1.22-3.40 01.52 0.91-2.56 .108

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87.e14 The American Journal of Medicine, Vol 123, No 1, January 2010

ack pain were associated with heterogeneity, which sug-ests differences in the etiology of low back pain in differ-nt countries and populations.

Former smokers had a lower risk of seeking care for lowack pain or chronic low back pain than current smokers,uggesting that the effects of smoking may be at least partlyeversible. We have, however, insufficient informationbout former smokers with regard to their exposure history,ncluding the duration and level of exposure, and time since

Table 5 Pooled Odds Ratio of Low Back Pain for Ever, Former,

irst Author Population Country

revalence (cross-sectional studies)Former smoking

Low back pain in the past monthNagasu26 Occupational JapanHeistaro27 General FinlandCroft25 General UKLeino-Arjas28 General Finland

PooledChronic low back pain

Leclerc41 General FranceBjörck-van Dijken43 General SwedenHeliövaara40 General Finland

PooledCurrent smoking

Low back pain in the past monthNagasu26 Occupational JapanHeistaro27 General FinlandCroft25 General UKLeino-Arjas28 General Finland

PooledLow back pain in the past 12 months

Hestbaek54 Twins DenmarkOksuz32 General Turkey

PooledSeeking care for low back pain

Mattila38 Conscripts FinlandLeino-Arjas28 General Finland

PooledChronic low back pain

Leclerc41 General FranceBjörck-van Dijken43 General SwedenHeliövaara40 General Finland

Pooledncidence (Cohort studies)

Low back pain in the past 12 monthsEver smoking

Andersen48 Occupational DenmarkLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

PooledFormer smoking

Andersen48 Occupational DenmarkLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

PooledCurrent smoking

Andersen48 Occupational DenmarkMikkonen57 Adolescents FinlandLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

Pooled

OR � odds ratio; CI � confidence interval.

topping smoking. t

The mechanisms of low back pain are only partly known.moking may lead to reduced perfusion and malnutrition of

he intervertebral discs via vasoconstriction,105 and in theong run, via atherosclerosis.106-108 Impaired blood supplyo spinal structures may cause degenerative lesions in thentervertebral discs109 and interfere with healing. Smokings a risk factor for osteoporosis,110,111 which may lead toow back pain.112 Smoking increases the level of circu-ating pro-inflammatory cytokines,113,114 which signal

rent Smokers versus Never Smokers in Males

Sample OR 95% CI

Heterogeneity No. ofModerateBiasesP Value I2 (95% CI)

1010 1.41 0.94-2.11 014,257 1.30 1.18-1.43 1

3905 1.45 1.15-1.83 13629 1.40 1.16-1.69 1

22,801 1.34 1.23-1.45 .77 0 (0-85)

7292 1.19 1.00-1.41 02850 1.44 1.11-1.86 02727 1.54 1.08-2.21 0

12,869 1.31 1.12-1.54 .28 19 (0-92)

1010 1.59 1.15-2.02 014,257 1.26 1.15-1.36 1

3905 1.29 1.12-1.74 13629 1.34 1.15-1.57 1

22,801 1.30 1.21-1.39 .45 0 (0-85)

4605 1.38 1.17-1.63 02164 1.20 1.00-1.50 16769 1.30 1.14-1.49 .29

7040 1.20 1.10-1.40 13629 1.46 1.18-1.80 1

10,669 1.30 1.07-1.57 .114

7292 1.24 1.06-1.46 02850 1.17 0.81-1.70 02727 1.68 1.28-2.21 0

12,869 1.35 1.09-1.66 .13 50 (0-85)

596 1.07 0.71-1.62 0353 1.59 1.06-2.37 0

1541 1.20 0.97-1.49 12490 1.24 1.04-1.48 .35 2 (0-90)

596 1.13 0.62-2.05 0353 2.15 1.23-3.76 0

1541 1.32 0.98-1.77 12490 1.44 1.04-1.98 .23 31 (0-93)

596 1.02 0.58-1.81 0410 1.38 0.71-2.67 0353 1.15 0.87-2.74 0

1541 1.08 0.79-1.48 12900 1.11 0.88-1.41 .90 0 (0-85)

or Cur

Year

2007199819941998

200820081991

2007199819941998

20062006

20081998

200820081991

200720062008

200720062008

2007200820062008

he central nervous system, leading to amplification of

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87.e15Shiri et al Association between Smoking and Low Back Pain

ain.115 Smoking changes the gene expression in interver-ebral discs; it down-regulates collagen genes and up-regu-ates aggrecan and the tissue inhibitor of metalloprotein-se-1 genes.116

ONCLUSIONSoth current and former smokers have a higher prevalencend incidence of low back pain than never smokers, but thessociation is fairly modest. The association is strongest forhronic or disabling low back pain. The association between

Table 6 Pooled Odds Ratios of Low Back Pain for Ever, Former

irst Author Population Country

revalence (Cross-sectional studies)Former smoking

Low back pain in the past monthNagasu26 Occupational JapanHeistaro27 General FinlandCroft25 General UKLeino-Arjas28 General Finland

PooledChronic low back pain

Leclerc41 General FranceBjörck-van Dijken43 General SwedenHeliövaara40 General Finland

PooledCurrent smoking

Low back pain in the past monthNagasu26 Occupational JapanHeistaro27 General FinlandCroft25 General UKLeino-Arjas28 General Finland

PooledLow back pain in the past 12 months

Hestbaek54 Twins DenmarkGhandour53 Adolescents USOksuz32 General Turkey

PooledChronic low back pain

Leclerc41 General FranceBjörck-van Dijken43 General SwedenHeliövaara40 General Finland

Pooledncidence (Cohort studies)

Low back pain in the past 12 monthsEver smoking

Andersen48 Occupational DenmarkLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

PooledFormer smoking

Andersen48 Occupational DenmarkLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

PooledCurrent smoking

AdultsAndersen48 Occupational DenmarkMikkonen57 Adolescents FinlandLeino-Arjas47 Occupational FinlandMiranda49 Occupational Finland

Pooled

OR � odds ratio; CI � confidence interval.

urrent smoking and the incidence of low back pain is s

tronger in adolescents than in adults. Research is needed tonvestigate whether smoking prevention or cessation is as-ociated with reduced incidence or severity of low backain.

CKNOWLEDGMENTSe thank Helena Liira for her assistance in selecting rele-

ant studies. We thank Johan Hviid Andersen, Christinajörck-van Dijken, Lise Hestbæk, and Helena Miranda for

rrent Smokers versus Never Smokers in Females

Sample OR 95% CI

Heterogeneity No. ofModerateBiasesP Value I2 (95% CI)

4825 1.31 0.98-1.73 014,786 1.26 1.09-1.45 1

5098 1.27 1.06-1.51 13915 1.13 0.91-1.39 1

28,624 1.24 1.13-1.36 .80 0 (0-85)

8242 1.33 1.11-1.60 02948 1.10 0.85-1.43 02946 0.85 0.57-1.27 0

14,136 1.13 0.90-1.43 .106 55 (0-87)

4825 1.61 1.29-2.00 014,786 0.99 0.89-1.10 1

5098 1.38 1.18-1.62 13915 1.17 0.98-1.39 1

28,624 1.25 1.01-1.55 �.001 86 (66-94)

4892 1.41 1.21-1.64 08250 1.40 1.10-1.90 12826 1.00 0.80-1.30 1

15,968 1.27 1.02-1.57 .05 66 (0-90)

8242 1.14 0.98-1.32 02948 1.43 1.07-1.92 02946 1.25 0.89-1.74 0

14,136 1.20 1.06-1.36 .38 0 (0-90)

824 1.00 0.67-1.49 0191 1.61 0.87-2.98 0538 0.99 0.66-1.46 1

1553 1.08 0.84-1.40 .37 0 (0-90)

824 1.01 0.59-1.74 0191 1.63 0.63-4.20 0538 0.89 0.50-1.58 1

1553 1.03 0.71-1.48 .56 0 (0-90)

824 0.99 0.55-1.79 0403 1.83 0.98-3.43 0191 1.60 0.71-3.57 0538 1.08 0.63-1.87 1

1956 1.27 0.93-1.74 .44 0 (0-85)

, or Cu

Year

2007199819941998

200820081991

2007199819941998

200620042006

200820081991

200720062008

200720062008

2007200820062008

ending us additional results.

R

studies) smoking and low back pain.

S

P

I

OR � odds ratio; CI � confidence interval.

87.e16 The American Journal of Medicine, Vol 123, No 1, January 2010

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Back Pain

Males Females

OR 95% CI OR 95% CI

1.34 1.23-1.45 1.24 1.13-1.361.30 1.21-1.39 1.25 1.01-1.55

1.30 1.14-1.49 1.27 1.02-1.57

1.30 1.07-1.57

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1.24 1.04-1.48 1.08 0.84-1.401.44 1.04-1.98 1.03 0.71-1.481.11 0.88-1.41 1.27 0.93-1.74

Figure 2 Funnel plot for publication bias in studies on theassociation between smoking and low back pain. (A) Cross-sectional studies on the association between ever (1 study) orcurrent (26 studies) smoking and low back pain; (B) Cohortstudies on the association between ever (1 study) or current (12

Table 7 Summary of Observed Association between Smoking and Low

moking

All

OR 95% CI

revalence (cross-sectional studies)Low back pain in the past month

Former smoking 1.27 1.20-1.35Current smoking 1.30 1.16-1.45

Low back pain in the past 12 monthsFormer smoking 1.20 1.00-1.44Current smoking 1.33 1.26-1.41

Seeking care for low back painFormer smoking 1.13 1.03-1.24Current smoking 1.49 1.38-1.60

Chronic low back painFormer smoking 1.24 1.11-1.38Current smoking 1.79 1.27-2.50

ncidence (cohort studies)Low back pain in the past 12 months

Ever smoking 1.21 1.04-1.42Former smoking 1.32 0.99-1.77Current smoking 1.31 1.11-1.55

resources/handbook/hbook.htm.

87.e17Shiri et al Association between Smoking and Low Back Pain

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79. Cecchi F, Debolini P, Lova RM, et al. Epidemiology of back pain ina representative cohort of Italian persons 65 years of age and older:the InCHIANTI study. Spine (Phila Pa 1976). 2006;31:1149-1155.

80. Omokhodion F. Low back pain among rural and urban populations inSouthwest Nigeria. Afr Newsl Occup Health Saf. 2002;12:57-59.

81. Omokhodion FO, Sanya AO. Risk factors for low back pain amongoffice workers in Ibadan, Southwest Nigeria. Occup Med (Lond).2003;53:287-289.

82. Jefferson JR, McGrath PJ. Back pain and peripheral joint pain in anindustrial setting. Arch Phys Med Rehabil. 1996;77:385-390.

83. Kopec JA, Sayre EC, Esdaile JM. Predictors of back pain in a generalpopulation cohort. Spine (Phila Pa 1976). 2004;29:70-77; discussion77-78.

84. Wijnhoven HA, de Vet HC, Smit HA, Picavet HS. Hormonal andreproductive factors are associated with chronic low back pain andchronic upper extremity pain in women—the MORGEN study. Spine(Phila Pa 1976). 2006;31:1496-1502.

85. Bejia I, Younes M, Jamila HB, et al. Prevalence and factors associ-ated to low back pain among hospital staff. Joint Bone Spine. 2005;72:254-259.

86. Hagen KB, Tambs K, Bjerkedal T. A prospective cohort study of riskfactors for disability retirement because of back pain in the generalworking population. Spine (Phila Pa 1976). 2002;27:1790-1796.

87. Videman T, Sarna S, Battié MC, et al. The long-term effects ofphysical loading and exercise lifestyles on back-related symptoms,disability, and spinal pathology among men. Spine (Phila Pa 1976).1995;20:699-709.

88. Symmons DP, van Hemert AM, Vandenbroucke JP, Valkenburg HA.A longitudinal study of back pain and radiological changes in thelumbar spines of middle aged women. I. Clinical findings. AnnRheum Dis. 1991;50(3):158-161.

89. Manninen P, Riihimak H, Heliövaara M. Incidence and risk factors oflow-back pain in middle-aged farmers. Occup Med (Lond). 1995;45:141-146.

90. Battié MC, Bigos SJ, Fisher LD, et al. A prospective study of the roleof cardiovascular risk factors and fitness in industrial back paincomplaints. Spine (Phila Pa 1976). 1989;14:141-147.

91. Biering-Sørensen F, Thomsen C. Medical, social and occupationalhistory as risk indicators for low-back trouble in a general population.Spine (Phila Pa 1976). 1986;11:720-725.

92. Vessey M, Painter R, Mant J. Oral contraception and other factors inrelation to back disorders in women: findings in a large cohort study.Contraception. 1999;60:331-335.

93. Spahn G, Schiele R, Langlotz A, Jung R. Prevalence of functionalpain of the back, the hip and the knee in adolescents. Results of across-sectional study [German]. Dtsch Med Wochenschr. 2004;129:2285-2290.

94. Vikat A, Rimpelä M, Salminen JJ, et al. Neck or shoulder pain andlow back pain in Finnish adolescents. Scand J Public Health. 2000;28:164-173.

95. Kristjansdottir G, Rhee H. Risk factors of back pain frequency inschoolchildren: a search for explanations to a public health problem.Acta Paediatr. 2002;91:849-854.

96. Bejia I, Abid N, Ben Salem K, et al. Low back pain in a cohort of 622Tunisian schoolchildren and adolescents: an epidemiological study.Eur Spine J. 2005;14:331-336.

97. Shipp EM, Cooper SP, Del Junco DJ, et al. Severe back pain amongfarmworker high school students from Starr County, Texas: baselineresults. Ann Epidemiol. 2007;17:132-141.

98. Harreby M, Kjer J, Hesselsoe G, Neergaard K. Epidemiologicalaspects and risk factors for low back pain in 38-year-old men andwomen: a 25-year prospective cohort study of 640 school children.Eur Spine J. 1996;5:312-318.

99. Mattila VM, Saarni L, Parkkari J, et al. Predictors of low back painhospitalization—a prospective follow-up of 57,408 adolescents.

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00. Buchanan AV, Weiss KM, Fullerton SM. Dissecting complex dis-ease: the quest for the Philosopher’s Stone? Int J Epidemiol. 2006;35:562-571.

01. Vogt MT, Hanscom B, Lauerman WC, Kang JD. Influence of smok-ing on the health status of spinal patients: the National Spine Networkdatabase. Spine (Phila Pa 1976). 2002;27:313-319.

02. California Environmental Protection Agency: Air Resources Board.Proposed identification of environmental tobacco smoke as a toxic aircontaminant (June 24, 2005). Tobacco Control. Surveys and ProgramEvaluations from Outside UCSF. Paper CALEPA2005. Available at:http://repositories.cdlib.org/tc/surveys/CALEPA2005.

03. Terrin N, Schmid CH, Lau J, Olkin I. Adjusting for publication biasin the presence of heterogeneity. Stat Med. 2003;22:2113-2126.

04. Peters JL, Sutton AJ, Jones DR, et al. Performance of the trim and fillmethod in the presence of publication bias and between-study heter-ogeneity. Stat Med. 2007;26:4544-4562.

05. Uematsu Y, Matuzaki H, Iwahashi M. Effects of nicotine on theintervertebral disc: an experimental study in rabbits. J Orthop Sci.2001;6:177-182.

06. Kauppila LI, McAlindon T, Evans S, et al. Disc degeneration/backpain and calcification of the abdominal aorta. A 25-year follow-upstudy in Framingham. Spine (Phila Pa 1976). 1997;22:1642-1647;discussion 1648-1649.

07. Shiri R, Viikari-Juntura E, Leino-Arjas P, et al. The associationbetween carotid intima-media thickness and sciatica. Semin Arthritis

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08. Korkiakoski A, Niinimäki J, Karppinen J, et al. Association of lumbararterial stenosis with low back symptoms: a cross-sectional studyusing two-dimensional time-of-flight magnetic resonance angiogra-phy. Acta Radiol. 2009;50:48-54.

09. Akmal M, Kesani A, Anand B, et al. Effect of nicotine on spinal disccells: a cellular mechanism for disc degeneration. Spine (Phila Pa1976). 2004;29:568-575.

10. Law MR, Hackshaw AK. A meta-analysis of cigarette smoking, bonemineral density and risk of hip fracture: recognition of a major effect.BMJ. 1997;315(7112):841-846.

11. Wong PK, Christie JJ, Wark JD. The effects of smoking on bonehealth. Clin Sci (Lond). 2007;113:233-241.

12. Hawker GA. The epidemiology of osteoporosis. J Rheumatol Suppl.1996;45:2-5.

13. O’Loughlin J, Lambert M, Karp I, et al. Association between ciga-rette smoking and C-reactive protein in a representative, population-based sample of adolescents. Nicotine Tob Res. 2008;10:525-532.

14. Yanbaeva DG, Dentener MA, Creutzberg EC, et al. Systemic effectsof smoking. Chest. 2007;131:1557-1566.

15. Watkins LR, Maier SF. The pain of being sick: implications ofimmune-to-brain communication for understanding pain. Annu RevPsychol. 2000;51:29-57.

16. Uei H, Matsuzaki H, Oda H, et al. Gene expression changes in anearly stage of intervertebral disc degeneration induced by passive

cigarette smoking. Spine (Phila Pa 1976). 2006;31:510-514.

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Appendix 1 Quality Assessment

ype of Bias Criteria Classification

election bias MajorSelection of study populationRepresentativeness (response rate, difference between

participants and nonparticipants, and control forvariables in case difference found betweenparticipants and nonparticipants)

MinorAwareness of study hypothesisPossibility of change in the status of a risk factor as

a result of low back pain

No or minor: Defined target population represents thegeneral population or subgroup of the generalpopulation (eg, women or men, certain age group,geographical area, certain occupational group) andresponse rate is above 60%.

Moderate: Defined target population represents anarrow subgroup of the general population andresponse rate is 80%-100%.

Severe: Defined target population represents a narrowsubgroup of the general population and responserate is 60%-80%.

Definite: Study population consists of “self-selected”volunteers if suspicion of payment to nonpatients.

erformance bias MajorValidity and objectivity of exposure assessment

MinorRecall biasBlinding of assessors of exposure towards the

outcome

No: Validated and systematic exposure assessment,blinding of assessors of exposure towards theoutcome.

Minor: No information on the number of cigarettessmoked per day or on the number of years smoked.

Moderate: Only one dichotomized question was usedfor the assessment of smoking, and never-smokerswere not distinguished from former smokers.

Definite: Nonsystematic exposure assessment,assessors of exposure not blinded towards theoutcome.

etection bias MajorClear definition of outcome

MinorStandardized method of assessing outcomeBlinding of assessors of outcome towards exposure

No or minor: Clear definition of outcome andstandardized method of assessing outcome.

Moderate: Clear definition of outcome and notstandardized method of assessing outcome.

Definite: Unclear definition of outcome ornonsystematic assessment of outcome.

ttrition bias MajorCompleteness of follow-upMagnitude of missing data

No: Participation rate 50%-100% for follow-up time�5 years, or comparison done for lost to follow-upabout variables of interest and less than 20% ofmissing data.

Possible: Participation rate 30-50% for follow-up time�5 years, and no comparison done for lost tofollow-up about variables of interest and missingdata between 20% and 40%.

Definite: Participation rate �30% for follow-up time�5 years or more than 40% of missing data.

Appendix 2 Studies Included in Meta-analyses on the Association between Smoking and Low Back Pain

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Adults

Cross-sectional studiesLow back pain in the past monthMiyamoto 2008,

Japan21Taxi drivers 24-79, mean

51.5Both 1334 Daily smokers vs

nonsmokersLow back pain in the

past 7 daysModerate No or

minorNo OR 1.65 (1.07-2.53) History of low back pain,

history of otherdiseases, fatigue,sleeplessness, regularexercise, long workinghours, burdensomeness

Schneider 2005,Germany22

Generalpopulation

18-79 Both 6235 Never, former, occasional,current smokers

Back pain during thepast 7 days

Minor No orminor

No OR 1.254 (1.091-1.442) forex-smokers, 1.177 (0.93-1.488) for occasional, 1.269(1.10-1.465) for currentsmokers

Age, sex, socioeconomicstatus, occupationalfactors, body massindex andpsychosocial factors

Brage 1996,Norway23

Generalpopulation

16-66 Both 6681 Never, former, currentsmokers.

Back pain in the past 2weeks

Minor Moderate No OR for current vs. neversmoking 1.84 (1.5-2.25)

Sex, age, co-morbidity,mental distress andwork-related physicalfactors

Ghaffari 2007,Iran24

Car manufacturingcompany

Not reported.majority�30 years

86.4%men

3838 Never, former, currentsmokers.

Low back pain in thepast 7 days

Minor No orminor

No OR 0.7 (0.4-1.2) for formerand 1.3 (1.0-1.6) forcurrent smoking

Adjusted for age, sex,physical work loads,psychosocial factorsand war participation

Croft 1994,UK25

Generalpopulation

18 or older Both 9003 (3905men and5098women)

Never, former, currentsmokers; number ofcigarettes per day

Low back pain in thepast month

No Moderate No Overall OR for current smoking1.4 (1.2-1.6). ORs forwomen: 1.27 (1.06-1.51),1.38 (1.18-1.62). ORs formen: 1.45 (1.15-1.83), 1.29(1.12-1.74). A dose-response relation withnumber of cigarettessmoked per day, which wasclearer for women than men.

Sex-specific ORs wereadjusted for age

Nagasu 2007,Japan26

Professional cooks Mean 41.4 formen, 47.5for women

Both, 83%women

5835 (1010men and4825women)

Never, former, currentsmokers.

Low back pain in thepast month

Minor No orminor

No Overall OR for former smoking1.35 (1.01-1.79), it was1.41 (0.94-2.11) for menand 1.31 (0.98-1.73) forwomen. Overall OR forcurrent smoking 1.57 (1.24-1.98). It was 1.59 (1.15-2.02) for men and 1.61(1.29-2.00) for women.

Sex-specific ORs wereadjusted for age.Overall ORs wereadjusted for sex,psychological factors,height of cookingequipment, kitchenenvironment and workactivities.

87.e21Shiri

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Pain

Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Heistaro 1998,Finland27

Generalpopulation

30-59 Both 29,043 (men14,257,women14786)

Never, former, currentsmokers.

Low back pain in thepast month

Minor Moderate No Overall OR 1.27 (1.17-1.37)for former and 1.16 (1.09-1.24) for current smoking.Men 1.30 (1.18-1.43) and1.26 (1.15-1.36). Women1.26 (1.09-1.45) and 0.99(0.89-1.10) for current.

Sex, age, education,income, workload,leisure time physicalactivity and BMI

Leino-Arjas1998,Finland28

Generalpopulation

20-64 Both 7544 (men3629,women3915)

Smoking classified 6groups: (1) never, (2)quit �12 m, (3) quit�12 m, (4)nonregular, (5) current1-20 cigarettes/day,(6) current �21cigarettes/d.

Back pain in the pastmonth

No Moderate No An association in men only.Among 3629 men ORs: 1.46(1.19-1.80), 1.18 (0.77-1.82), 1.15 (0.84-1.57),1.34 (1.10-1.63) and 1.35(1.05-1.74).

Age, marital status,height, BMI, mentalstress, occupationalclass and physicalactivity

Low back pain in the past 12 monthsStrine 2007,

US7General

population18 or older Both 29828 Current smokers vs

nonsmokersLow back pain for at

least a day in the past3 months

Moderate No orminor

No OR 1.3 (1.2-1.4) Age, sex, race/ethnicity,education, maritalstatus, employmentstatus, number andtype of comorbidcondition

Leboeuf-Yde1996,29

1997,30

Denmark

Generalpopulation

30-50 Both 1370 Never smokers, formersmokers, currentsmokers 1-10 cig/day,11-20 cig/day, currentsmokers �20 cig/day

Low back pain at least aday or for �30 days inthe past 12 months

No No orminor

No OR for current smoking 1.3(1.0-1.6) for low back pain�1 day, 1.0 (0.7-1.3) forlow back pain 8-30 days.

Unadjusted. OR remainedsignificant afteradjustment for age,sex, marital status andphysical activity atwork.

Leboeuf-Yde1998,Denmark31

Twins 12-41 Both 29424 Never, former, currentsmokers. Number ofcigarettes smoked andnumber of yearssmoked.

Low back pain for 1-7days or 8-30 days inthe past 12 months

No No orminor

No OR 1.4 (1.3-1.6) for low backpain 1-7 days, and 2.1(2.0-2.2) for 8-30. No dose-response relations withnumber of cigarettessmoked and number ofyears smoked. Low backpain also was high in ex-smokers regardless ofnumber of years sincesmoking cessation. Noassociation betweensmoking and low back painin monozygotic twins.

Unadjusted. Results didnot change whenanalysis stratified byage, sex or BMI.

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Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Oksuz 2006,Turkey32

Generalpopulation

18-70, mean39.5

Both 4990 (2164men and2826women)

Current smokers vsnonsmokers

Low back pain for morethan a day in the past12 months

Moderate No orminor

No OR 1.2 (1.0-1.5) for men 1.0(0.8-1.3) for women.Overall 1.1 (0.9-1.3)

Sex-specific ORs adjustedfor age, BMI,education and livinglocation. Overall ORadjusted for abovevariables and sex,occupation andphysical stress

Skov 1996,Denmark33

Salespeople Mean age42.0 � 9.9years (men)and36.5 � 7.8years(women)

Both 1306 Never, former, currentsmokers

Low back pain in thepast 12 months

Minor No orminor

No OR 1.51 (1.09-2.10) for formerand 1.31 (0.98-1.76) forcurrent smoking

Social contact withcolleagues, annualdriving distance,sedentary work,tendency to feeloverworked, height

Wright 1995,UK34

Generalpopulation

18 or older Both 38,011,23,500-24,800 formultivariable

Never, former, currentsmokers (pipe, cigarsor 1-14 cigarettes/day), current smokers(�15 cigarettes/day)

Sciatica, lumbago orrecurring backache inthe past 12 months

No No orminor

Possible ORs were 1.20 (1.11-1.30),1.27 (1.16-1.40), and 1.45(1.33-1.58).

Age, sex, height, alcoholconsumption, BMI,physical activity, diet,living alone, andpsychologicalproblems

Pietri 1992,France35

Commercialtravellers,salesperson

Mean age 38.7for men,37.6 forwomen

Both 1709 (men1368,women 341)

Never, former, currentsmokers.

Low back pain in thepast 12 months

Minor No orminor

No OR 1.4 (1.1-1.7) for current/past smoking vs. neversmoking

Age, sex, driving,comfort of the carseat, carrying loads,standing, andpsychosomatic factors

Raanaas 2008,Norway36

Taxi drivers Mean age 43.3 Both,majorityweremen

823 Often/very frequent vsnever/seldom

Low back pain in thepast 12 months

Moderate No orminor

No OR 0.99 (.73-1.34) Age, sex, ethnic origin,driving hours perweek, BMI, physicalactivity and violenceexposure

Karahan 2009,Turkey37

Hospital staff Mean age 28 Both,majoritywerewomen(69%)

1510 Current smokers vsnonsmokers

Low back pain for atleast a day in the past12 months

Moderate No orminor

No OR 1.52 (1.19-1.95) Sex, occupation, workingyears, exercise,perceived stress inwork environment andphysical work loadfactors

Seeking care for low back painLeino-Arjas

1998,Finland28

Generalpopulation

20-64 Both 7544 (3915men and3629women)

Smoking classified 6groups: 1) never, 2)quit �12 m, 3) quit�12 m, 4) nonregular,5) current 1-20cigarettes/day, 6)current �21cigarettes/d.

Back pain with medicalconsultation in thepast 12 months

No Moderate No In men OR was 1.40 (1.06-1.83) for current smoking1-20 cigarettes/day and1.54 (1.11-2.14) for current�21 cigarettes. In womencorresponding ORs were1.23 (0.93-1.62) and 1.69(0.85-3.35).

Age, marital status,height, BMI, mentalstress, occupationalclass and physicalactivity

87.e23Shiri

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Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Wright 1995,UK34

Generalpopulation

18 or older Both 34,141(23,500-24,800 formultivariableanalysis)

Never, former, currentsmokers (pipe, cigarsor 1-14 cigarettes/day), current smokers(�15 cigarettes/day)

Consultation for sciatica,lumbago or recurringbackache in the past12 months

No No orminor

Possible ORs 1.14 (1.03-1.26), 1.49(1.32-1.68), 1.52 (1.36-1.70)

Age, sex, height, alcoholconsumption, BMI,physical activity, diet,living alone, andpsychologicalproblems

Mattila 2008,Finland38

Conscripts 18-29, median19

Men 7040 Daily smoking, use ofsmokeless tobacco

Lifetime low back painprompting a visit to aphysician

Moderate No orminor

No Age-adjusted OR 1.2 (1.1-1.4)for daily smoking. AdjustedOR 1.4 (1.2-1.7) forsmokeless tobacco use

AgeAge, self-perceived

health status,number of diseasesand physical activity.

Chronic low back painSilva 2004,

Brazil39General

population20 or older Both 3182 Never, former, current

smokers.Chronic low back pain

(pain longer than 7weeks)

Minor No orminor

No OR: 1.64 (0.88-3.05), 2.36(1.49-3.74)

Age, sex, marital status,education, BMI, work-related physicalfactors

Heliövaara1991,Finland40

Generalpopulation

30-64 Both 5673 (2727men and2946women)

Never, former, currentsmokers (pipe, cigarsor 1-19 cigarettes/day), current smokers(�20 cigarettes/day)

Chronic nonspecific lowback pain

No No orminor

No OR: 1, 1.2 (1.0-1.6), 1.3 (1.0-1.7), 1.5 (1.1-2.1). Inthose aged 30-49, formerand current smoking wasassociated with low backpain only in men and notin women. In those aged50-64 only smoking �20cigarettes/day associatedwith low back pain in bothmen and women.

Age, sex, physical workload, occupationalmental stress,traumatic back injury,smoking and alcoholconsumption

Leboeuf-Yde199629 and1997,30

Denmark

Generalpopulation

30-50 Both 1370 Never smokers, formersmokers, currentsmokers 1-10 cig/day,11-20 cig/day, currentsmokers �20 cig/day.

Low back pain for morethan 30 days in thepast 12 months

No No orminor

No OR for current smoking 2.3(95% CI, 1.6-3.3). A dose-response relation.

Unadjusted. OR remainedsignificant afterstratifying for age,sex, marital status andphysical activity atwork.

Leboeuf-Yde1998,Denmark31

Twins 12-41 Both 29,424 Never, former, currentsmokers. Number ofcigarettes smoked andnumber of yearssmoked.

Low back pain more than30 days in the past 12months

No No orminor

No OR for current smoking 3.0(2.8-3.3). No dose-responserelations with number ofcigarettes smoked andnumber of years smoked.Low back pain also washigh in ex-smokersregardless of number ofyears since smokingcessation. No associationbetween smoking and lowback pain in monozygotictwins.

Unadjusted. Results didnot change whenanalysis stratified byage, sex, or BMI.

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Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Leclerc 2009,France41

Generalpopulation

30-69 Both 15,534 (7292men and8242women)

Never, former, currentsmokers

Low back pain more than30 days in the past 12months

Minor No orminor

No OR 1.19 (1.00-1.41) and 1.24(1.06-1.46) for men. ORs1.33 (1.11-1.60) and 1.14(0.98-1.32) for women.

Age, education, personalfactors, physicalconstraints at work

Andersson1998,Sweden42

Generalpopulation

25-74 Both 1624 Never, former, currentsmokers (1-9, 10-19,�20 cigarettes/day)

Chronic low back pain(moderate to severepain longer than 6months) � radiatingpain to the legs

No No orminor

No OR 1.66 (1.19-2.32) for formerand 1.58 (1.13-2.20) forcurrent smoking. A doseresponse relation with dailysmoking.

Age, sex, education,socioeconomic level,sleep disturbance,depression and highwork strain

Björck-vanDijken 2008,Sweden43

Generalpopulation

25-79 Both 5798 (2850men, 2948women)

Never, former, currentsmokers. Number ofcigarettes smoked.

Low back pain lastedcontinuously for morethan 6 months

No No orminor

No ORs were 1.44 (1.11-1.86) and1.17 (0.81-1.70) for menand 1.10 (0.85-1.43) and1.43 (1.07-1.92) forwomen.

Age, education, physicalactivity at work,occurrence of physicaldemanding work, lowphysical activityduring leisure timeand BMI

Disabling low back painLiira 1996,

Canada44General

population16-64 Both 18920 Nonsmokers, occasional,

current smokers.Long-term back problems

(serious back pain orback problem led to along-term healthproblem or to alimitation in activity)

Moderate No orminor

No OR 1.55 (1.20-2.00) forsmokers vs nonsmokers

Age, sex, occupationalclass, work-relatedphysical exposure

Cohort studies1-year incidence of low back painEriksen 1999,

Norway45General

population20-72 at

baseline,4-yearfollow-up

Both 562 Daily smokers vsnonsmokers

Low back pain in thepast 12 months

Moderate No orminor

No Overall ns. OR 1.11 (0.68-1.82). Interaction withheavy physical work. OR oflow back pain 5.53 (1.93-15.84) in smokers and 1.12(0.48-2.59) in nonsmokerswith both lifting andstanding.

Sex, age, marital status,physical activity, painother low back pain,monotonousmovements in the job,and emotionalsymptoms

87.e25Shiri

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Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Power 2001,GreatBritain46

Generalpopulation

23 at entry,10-yearfollow-up

Both 5781 (2773 formultivariableanalysis)

Smoking classified into 5groups: 1) neversmoked, 2) neversmoked moderately orheavily (�10cigarettes/d), 3) earlymoderate or heavysmoking (at or before23 years) and cessationby 33, 4) earlymoderate or heavysmoking continuing at33 years, 5) lateinitiation (startedmoderate or heavysmoking between 23and 33).

1-year incidence of backpain lasted for morethan a day at ages 32to 33

No No orminor

Possible Only early and continuedsmoking was associatedwith back pain OR 1.63(1.23-2.17).

OR for early andcontinued smokingwas adjusted for sex,BMI, social class,ergonomic andpsychosocial factors.

OR 1.03 (0.77-1.38) for earlyand quit smoking, and 0.97(0.59-1.59) for lateinitiation.

ORs for early and quitsmoking and for lateinitiation wereunadjusted.

Leino-Arjas2006,Finland47

Metal industryemployees

18-64 atbaseline,28-yearfollow-up

Both 544 (353 menand 191women)

Never, former, currentsmokers.

Frequent local low backpain (rather often orcontinuously) in past12 months

Minor No orminor

No In men, OR 2.15 (1.23-3.76)for former and 1.15 (0.87-2.74) for current smoking.In women, OR 1.63 (0.63-4.20) and 1.60 (0.71-3.57).

Sex-specific analysiscontrolled for age andoccupational class

Pietri 1992,France35

Commercialtravelers,salesperson

Mean age 38.7for men,37.6 forwomen,1-yearfollow-up

Both 627 (men 514,women 113)

Never, former, currentsmokers.

1-year incidence of lowback pain

Minor No orminor

Possible OR 1.3 (0.8-2.1) for current/past smoking vs neversmoking

Age, sex, driving,comfort of the carseat, carrying loads,standing, andpsychosomatic factors

Andersen 2007,Denmark48

Workers fromindustrial andservicecompanies

Mean 45 � 10,2-yearfollow-up

Both 1513 Never, former, currentsmokers.

Bother some to verymuch by low back painin the past 12 months

Minor No orminor

No ORs were 1.13 (0.62-2.05) and1.02 (0.58-1.81) for menand 1.01 (0.59-1.74) and0.99 (0.55-1.79) forwomen.

Age, occupational group,intervention group,lifting, standing andjob control

Miranda 2008,Finland49

Forest industryworkers

16.4-65.0 Both,majorityweremen

2256 (1676 formultivariableanalysis)

Never, former, currentsmokers.

1-year incidence of lowback pain � 7 days

Minor No orminor

Possible An association in subjectsaged 50 or older

Age, sex, heavy lifting,awkward postures,whole-body vibration,body mass index andphysical exercise

Sickness absence due to low back painGhaffari 2007,

Iran24Car manufacturing

companyNot reported.

majority�30 years

86.4%men

3838 Never, former, currentsmokers.

1-year incidence ofsickness absence dueto low back pain (�1day)

Minor No orminor

No OR 0.9 (0.1-7.4) for formerand 3.1 (1.6-6.2) forcurrent.

Adjusted for age, sex,physical work loads,psychosocial factorsand war participation

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Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Hemingway1999,England50

Nonindustrial civilservants

35-55, 4-yearfollow-up

Both 4886 (3506men, 1380women)

Never, former, currentsmokers �15 pyrs,current smokers 15-29pyrs, current smokers�30 pyrs

Sickness absence due toback pain (��7 daysor � 7 days)

No No orminor

No ns in men. A significantassociation in women forsickness absence for 7 daysor less.

Age, BMI, employmentgrade, baseline backpain

Van den Heuvel2004, TheNetherlands51

Workingpopulation

Not reported,3-yearfollow-up

Both 629 Never, former, currentsmokers

Sickness absence due toback pain (�1 days)in the past 12 months

Minor No orminor

Possible OR 0.73 (0.33-1.58) and 0.80(0.41-1.57)

Sex, age, BMI, physicalactivity, work-relatedphysical load factors,psychosocial factorsand paincharacteristics atbaseline

Tubach 2002,France52

Workers ofnationalelectricity andgas company

35-50, 4-yearfollow-up

Both 2236 Nonsmokers, currentsmokers 1-10 cig,current smokers 11-20cig, current smokers�21 cig.

Low back pain for morethan 30 days andsickness absence �8days in the past 12months

Minor No orminor

No ORs 1.2 (0.5-3.1) for lightsmoking, 1.2 (0.5-2.9) formedium and 5.5 (2.3-13.0)for heavy smoking

Sex, physical loadsfactors, pain atbaseline, socialsupport at work,, andpsychological demand

Adolescents

Cross-sectional studiesLow back pain in the past 12 monthsGhandour 2004,

US53School children Grade 6-10 Girls 8250 Smokers vs nonsmokers Back pain at least once a

week in the past 6months

Moderate No orminor

No OR 1.4 (1.1-1.9) Age, race/ethnicity,mother’s education,parent support,teacher support,student support, bullyexperience, alcoholuse, coffee intake,physical activity

Hestbaek 2006,Denmark54

Twins 11-22 Both 9497 (4605boys and4892 girls)

Nonsmokers, smokers 1-10 cig/day, smokers11-20 cig/day, smokers�20 cig/day

Low back pain in thepast 12 months

No No orminor

No For current smoking OR was1.38 (1.17-1.63) in boysand 1.41 (1.21-1.64) ingirls

Age and BMI

Chronic low back painHestbaek 2006,

Denmark54Twins 11-22 Both 9608 Nonsmokers, smokers 1-

10 cig/day, smokers11-20 cig/day, smokers�20 cig/day.

Low back pain for morethan 30 days in thepast 12 months

No No orminor

No OR 1.77 (1.44-2.17) for eversmoking. Smoking 4 groups:1, 1.38 (1.02-1.88), 2.00(1.53-2.63), 6.38 (2.66-15.35).

Sex, age, BMI andalcohol consumption

Disabling low back painHarreby 1999,

Denmark55School children 13-16 Both 1389 Daily smoking vs less

frequent smoking.Number of cigarettessmoked daily.

Severe low back pain(recurrent orcontinuous pain inmoderate to severedegree)

No No orminor

No OR 3.03 (2.14-4.30) Sex and heavy job inleisure time

87.e27Shiri

etal

Associationbetw

eenSm

okingand

LowBack

Pain

Appendix 2 Continued

Author, Yearand Country Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment for OtherCovariatesPerformance Detection Attrition

Cohort studiesFeldman 199956

and 2001,6

Canada

School children 12-14 (grade7-9), 1-yearfollow-up

Both 377 Nonsmokers, currentsmokers 1-25cigarettes/week,current smokers �25cigarettes/week

Low back pain at leastonce a week in thepast 6 months

No No orminor

No OR 2.20 (1.38-3.50) forcurrent vs nonsmokers. OR2.28 (1.15-4.51) for lightto moderate smoking and3.78 (0.82-17.51) formoderate to heavysmoking.

Age, sex, height, sportsactivity, work activity,mental health status,high growth spurt,poor abdominalstrength and poormuscular flexibility

Mikkonen 2008,Finland57

Adolescents 16 at baseline,2-yearfollow-up

Both 813 Regular smokers vs neveror occasional smokers,number of cigarettesper day (1-9 or over 9cigarettes/day)

Low back pain in thepast 6 months

No No orminor

No For regular smoking OR was1.38 (0.71-2.67) in boysand 1.83 (0.98-3.43) ingirls. OR was 1.72 (0.85-3.50) for 1-9 cig/d and1.71 (0.72-4.01) for �9cig/d in boys. In girls 1.32(0.73-2.41) and 2.80 (1.11-7.09).

Parents’ socioeconomicstatus, physicalactivity, body massindex, and depressivemood

Mustard 2005,Canada58

School children 4-16 atbaseline,21-34 atfollow-up,18-yearfollow-up

Both 1039 Nonsmokers, currentsmokers 1-9 cigarettes/day), current smokers(�10 cigarettes/day).Smoking was assessedat follow-up.

Low back pain in thepast 12 months

Minor Moderate Possible ORs 1.63 (0.92-2.91) and 1.85(1.10-3.10)

Age, sex, education,parental education,body mass index, jobdemands, psychosocialwork conditions, worksocial support, jobsatisfaction, mentalhealth, social support,factional limitations

OR � odds ratio; CI � confidence interval; BMI � body mass index; pyrs � pack-years; NS � non-significant.

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Appendix 3 Studies Not Included in Meta-analyses on the Association between Smoking and Low Back Pain

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Adults

Cross-sectional studiesLow back pain in the past monthBergenudd 1994,

Sweden59General

population55 Both 575 (men

323,women252)

Smokers vs nonsmokers Current back pain No orminor

Moderate No orminor

No ns Overweight, sleepingdisturbance, jobsatisfaction, andoccupationalworkload

Ueno 1999,Japan60

Constructionworkers

20-70 Men 2289 Smoking classified 4 groups:1) never, 2) former, 3)current �20 cigarettes/day, 4) current �20cigarettes/day

Current low back pain No orminor

No No orminor

No OR for any low backpain: 0.95 (0.73-1.25), 1.13 (0.87-1.47), 1.14(0.87-1.52).

OR for relatively severelow back pain: 1.05(0.71-1.58), 0.97(0.66-1.45), 1.47(1.00-2.16).

Unadjusted

Kostova 2001,Bulgaria61

Operators, repairstaffs, shopmanagers,administrators,laboratoryassistants,other

Not reported Both 898 Nonsmokers vs currentsmokers, smoking �20years vs. �20 years,smoking �20 cigarettes/day vs �20 cigarettes/day

Current low back painfor a week or more

Moderate No No No OR 0.82 (0.59-1.15) forcurrent smoking. OR1.24 (0.76-2.02) forsmoking over 20 years.OR 0.83 (0.43-1.57)for smoking over 20cigarettes/day.

Unadjusted

Brynhildsen1998,Sweden62

Generalpopulation

55-56 Women 1103 Smokers vs nonsmokers Current back pain (inthe past week)

No orminor

Moderate No orminor

No Overall no association. Aninteraction betweensmoking and anoccupation requiringheavy lifting orphysical stress(P � .01)

Unadjusted

Svensson 1983,Sweden63

Generalpopulation

40-47 Men 716 Former or current vs neversmokers; number of yearsof smoking

Current low back painor low back painoccurring at leastonce a month,current severe pain(ongoing eitherdaily or recurring�2 times a week)

No orminor

Minor No orminor

No No association. Numberof years of smokingassociated with severecurrent pain

Unadjusted

Landry 2008,Kuwait64

Hospital workers 20 or older Both 344 Smokers vs nonsmokers Low back pain in thepast 24 h

Moderate Moderate No orminor

No ns Unadjusted

Lagerström1995,Sweden65

Nursingpersonnel

18-64 Women 688 Smokers vs nonsmokers Current low backpain, severe lowback pain (�6 onthe scale of 0-9)

Moderate Moderate No orminor

No OR 1.17 (0.84-3.47) forany low back pain and1.07 (0.87-1.65) forsevere low back pain.

Unadjusted

87.e29Shiri

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Associationbetw

eenSm

okingand

LowBack

Pain

Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Mazicioglu 2006,Turkey66

Pregnant women Mean age 27.1(SD 9.9)

Women 1357 Never, former, currentsmokers

Current low back pain Moderate Minor No orminor

No OR .82 (0.39-1.73) fornonsmokers, 0.45(0.19-1.03) for formersmokers. Currentsmokers were used as areference group.

Previous pain,weight, assistantin daily activities,Oswestry backpain scale.

Miyamoto 2000,Japan67

Truck drivers 19-61, meanage 41.6

97% men 153 (148men, 5women)

Smokers vs nonsmokers Low back pain in thepast month

No orminor

Moderate No orminor

No OR 1.8 (0.7-4.5) Unadjusted

Hartvigsen2003,68

2004,69

Denmark

Twins 70-102 Both 4484 Never, former, currentsmokers.

Back pain, acute lowback pain or lumbagoin the past month

No orminor

Minor No orminor

No ns. OR not reported Sex-specificunadjusted

Low back pain in the past 12 monthsTiwari 2003,

India70Cotton textile

workers68% were 25-

35 yearsNot

reported514 Smokers vs nonsmokers Low back pain in the

past 6 monthsModerate Moderate Moderate No OR 2.19 (1.23-3.89) Unadjusted

Deyo 1989, US71 Generalpopulation

25 or older Both 10404 Never, former, currentsmokers. Packs per dayclassified into 5 groupsand pack-years into 6groups.

Low back pain in thepast 12 months

No orminor

No No orminor

No Dose-response relationsbetween current levelof smoking and pack-years of smoking, andlow back pain. OR 1.05for each increasingpack-decade. In bothsexes these dose-responses wereapparent only in thoseunder age 45. Smokingcessation reduced therisk of low back pain.

Age, education,employmentstatus, BMI,chronic cough,level of dailyactivity

Ghaffari 2006,Iran72

Car-manufacturingindustry

Not reported.majority�30 years

96% men 10941 Smokers vs nonsmokers Low back pain in thepast 7 days

No orminor

Moderate No orminor

No ns. OR not reported Adjusted for age,physical andpsychosocialfactors

Videman 2005,Finland73

Nursing students Mean age 22.6(SD 4.5), a7.5-yearfollow-up

Women 174 Ever smokers vs nonsmokers Back pain in the past 12months

Moderate Moderate No orminor

No OR 1.2 (0.4-3.7) forsudden back pain and2.0 (0.7-5.9) for backpain other than sciaticor sudden pain.

Previous back pain,patient handlingskill, sit-ups,twisted-bent workposition, andhysteria score.

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Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Niedhammer1994, France74

Nurses Mean age 30 Women 310 Current smokers vsnonsmokers

Lumbar pain in the past12 months

Moderate Moderate No orminor

No OR 1.23, not significant(CIs not reported)

Age, sportsactivities,previousmusculoskeletaldisorders, physicalwork load,symptoms ofpsychologicaldisorders, andpsychosocialfactors at work

Lehto 1991,Finland75

Dentists 33-65, mean46

Both 131,42 men89 women

Smokers vs nonsmokers Low back pain in thepast 12 monthsinterferes with dailyactivities

No orminor

Moderate No orminor

No ns Sex-specificunadjusted

Alcouffe 1999,France76

Workers of smallcompanies

15-73, mean37.8 formen 37 forwomen

Both 6827 Smokers vs nonsmokers Low back pain in thepast 12months � radiatingpain to the legs

No orminor

Moderate No orminor

No OR 1.15 (1.01-1.32) formen 1.21 (1.03-1.41)for women and 1.17(1.06-1.30) overall.

Sex-specificunadjusted

Holmström 1992,Sweden77

Constructionworkers

18-65, mean39.5 (12.5)

Men 1773 (1772men, 1woman)

Never, former, currentsmokers

Low back pain at least aday in the past 12months � radiatingpain to the legs.

No orminor

Minor No orminor

No OR for current smoking1.07 (0.97-1.18).

Unadjusted

Toroptsova 1995,Russia78

Employees ofmachinebuildingfactory

18-65, mean41.2

Both 583 Smokers vs nonsmokers.Smokers �10 vs �10cigarettes/day

Low back pain lastinglonger than a day inthe past 12 months

No orminor

Moderate No orminor

No No association. There wasa tendency toward ahigher low back painin the group of heavysmokers.

Unadjusted

Cecchi 2006,Italy79

Generalpopulation

65 or older Both 1008 Former or current vs neversmokers

Frequent low back painin the past 12months

No orminor

Moderate No orminor

No ns Unadjusted

Omokhodion200280 and2003,81

Nigeria

Office workers 20-60 Both 840 Never, former, currentsmokers

Low back pain in thepast 12 months

No orminor

Minor No orminor

No Association betweencurrent smoking andlow back pain.Prevalence was 57% incurrent smokers vs36% in never smokers.OR not reported.

Unadjusted

Jefferson 1996,Canada82

Employees of anaircraft enginefactory

Not reported Notreported

306 Smokers vs nonsmokers Low back pain in thepast 12 months

No orminor

Moderate No orminor

No ns Unadjusted

87.e31Shiri

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Associationbetw

eenSm

okingand

LowBack

Pain

Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Seeking care for low back painKopec 2004,

Canada83General

population18 or older,

2-yearfollow-up

Both 10,007 Never, former, currentsmokers. Number of yearssmoked

Consultation for a backpain lasted 6 monthsor longer.

No orminor

Minor No orminor

No ns. Number of yearssmoked was associatedwith back pain in menin unadjusted modelonly.

Smoking did notremain significantin the backwardeliminationprocedure.

Chronic low back painWijnhoven,

2006, theNetherlands84

Generalpopulation

20-59 Women 11428 Current vs former/neversmokers

Chronic low back pain(�12 weeks) in thepast 12 months

No orminor

Moderate No orminor

No OR 1.14 (0.98-1.32) Age, working status,education,overweight,hormonal andreproductivefactors

Bejia 2005,Tunisia85

Hospitalemployees

18-60, mean37 (7.8)

Both 350 Smokers vs nonsmokers Chronic low back pain(�3 months)

Moderate Moderate No orminor

No No association (OR notreported).

Age, sex, BMI,marital status,sports activity,psychologicalproblems, lowback pain pastmedical history,and extraprofessionalactivity

Disabling low back painHagen 2002,

Norway86Working

population25-59 years, a

7-yearfollow-up

Both 24,538 Current smokers vsnonsmokers

Disability retirementfrom back pain

No orminor

Moderate Moderate No OR 1.4 (1.2-1.7) Sex, age, body massindex, physicallydemanding work,perceived generalhealth, diabetes,angina pectoris,and worn out

Holmström 1992,Sweden77

Constructionworkers

18-65, mean39.5 (12.5)

Men 1773 (1772men, 1woman)

Never, former, currentsmokers.

Severe low back pain(often or very oftenfor 8-30 days andwith very severefunctionalimpairment)

No orminor

Minor No orminor

No OR for current smoking2.67 (2.0-3.4)

Unadjusted

Case control studyVideman 1995,

Finland87Former elite

athletes(cases),eligible menfor militaryservice(controls)

�65 Men 937 � 620 Smokers vs nonsmokers Low back pain in thepast years interferingwith working

Moderate Moderate Moderate No OR 1.3 (CI not reported).It was statisticallysignificant.

Age

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Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Cohort studiesSymmons 1991,

theNetherlands88

Generalpopulation

45-64 atbaseline,9-yearfollow-up

Women 241incidence,236recurrent

Current smokers vsnonsmokers

Current back pain orexperiencedcontinuous back painfor �2 weeks duringfollow-up

No orminor

Minor Moderate No No association. OR forincidence 0.78 (0.47-1.30) and forrecurrence 1.03 (0.85-1.25)

Unadjusted

Manninen 1995,Finland89

Farmers 45-54, 12-yearfollow-up

Both 363, 193men, 170women

Never, former, currentsmokers. Pack-yearsclassified into 4 groups(0-7.2, 7.3-15.0, 15.1-30.0, �30.0).

Low back pain in thepast 12 months

Moderate No No orminor

Possible ns. OR in men 1, 0.63(0.22-1.78), 0.71(0.24-2.11)

Sex-specific analysescontrolled for age,height, mentalstress, smoking,farm productionand occupationalclass

Battie 1989,US90

Aircraftmanufacturingemployees

21-67 atbaseline,4-yearfollow-up

Both 3020 Current smokers vsnonsmokers

Incidence of back painor injury

No orminor

Moderate No orminor

No Smoking increased theincidence of backproblems (RR 1.4, CInot reported)

Age and sex

Biering-Sørensen1986,Denmark91

Generalpopulation

30-60 atbaseline,1-yearfollow-up

Both 920 Daily smokers vsnonsmokers

Incidence of low backpain in the past 12months, andrecurrence/persistence

No orminor

Moderate No orminor

No Smoking associated witha higher incidence oflow back pain. Noassociation withrecurrence orpersistence low backpain.

Sex, age, epigastricpain, colic, poorhealth,hospitalization,distance fromhome to work

Niedhammer1994, France74

Nurses Mean age 30,a 5-yearfollow-up

Women 208 Current smokers vsnonsmokers

Lumbar pain in the past12 months

Moderate Moderate No orminor

No ns Age, sportsactivities, physicalwork load,symptoms ofpsychologicaldisorders,psychosocialfactors at workand commuting

Vessey 1999,UK92

Women attendingfamilyplanningclinics

25-39 atbaseline,26-yearfollow-up

Women 17032 Nonsmokers, smokers Referral to hospital dueto unspecifiedbackache

Moderate Moderate No orminor

No ns Unadjusted

87.e33Shiri

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okingand

LowBack

Pain

Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Adolescents

Cross-sectional studiesSpahn 2004,

Germany93School children Mean age 14.5

(0.7)Both 2368 Never, occasional, regular

smokers.Low back pain in the

past 3 monthsNo or

minorNo No or

minorNo A significant association.

Prevalence of low backpain was 32.6% innever smokers, 34.2%in occasional and39.5% in regularsmokers.

Unadjusted

Vikat, 2000Finland94

Generalpopulation,adolescent

14-18 Both 10302 Smoking classified 6 groups:1) never smoked, 2) onlyonce, 3) 2-50 cigarettesever, 4) more than 50cigarettes ever, 5) lessthan 10 cigarettes daily,6) 10 or more cigarettesdaily

Low back pain at leastonce a week in thepast 6 months

No orminor

No No orminor

No ORs: CIs are not reported1) 1 (reference group)2) 1.4 (significant)3) 1.24) 1.6 (significant)5) 2.0 (significant)6) 2.2 (significant)

Age, sex, timing ofpuberty, familybackground,physical activity,school enrolmentand success, long-term illness andpsychosomaticsymptoms

Kristjansdottir2002,Iceland95

School children 11-16 Both 2173 Smoking was measured byhow often subjectssmoked per week(0 � never to 6 � onceor more every day).

Recurrent back pain (atleast weekly)

No orminor

Minor No orminor

No Smoking was associatedin the univariablemodel, but did notremain significant atthe stepwise regressionmodel.

Age, chronic diseaseor handicap,tiredness, physicalfitness, coffeedrink, andparental supportwere included inthe stepwisemodel.

Bejia 2005,Tunisia96

School children 11-19 Both 622 Smokers vs nonsmokers chronic low back pain(pain lasted �3months andoccurred � once aweek)

Moderate Moderate No orminor

No No association Unadjusted

Shipp 2007, US97 Farm workers Majority 14-18years

Both 306 Current use of tobacco(cigarettes, cigars, orchew)

Severe back pain in thepast 9 months (lastedevery day for 1�weeks or resulted inloss of 4� hours fromregular activity orresulted in medicaltreatment)

Moderate Minor Moderate No OR 2.79 (1.23-6.31) Sex, history of backinjury, physicalwork load factorsand feeling tenseor stressed oranxious.

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Appendix 3 Continued

Author, Year andCountry Study Population

Age Range(Years) Sex

Sample Size(in Analysis) Smoking Outcome

Assessment of Quality: Biases

Results OR (95% CI)Adjustment forOther CovariatesSelection Performance Detection Attrition

Cohort studiesChronic low back painHestbaek 2006,

Denmark54Twins 11-22 at

baseline,8-yearfollow-up

Both 6554 Nonsmokers, smokers 1-10cig/day, smokers 11-20cig/day, smokers �20cig/day

Low back pain for morethan 30 days in thepast 12 months

No orminor

No No orminor

No OR 1.88 (1.32-2.69) forcurrent smoking.Smoking 4 groups: 1,1.76 (1.10-2.82), 2.12(1.30-3.46), -.

Sex, age, BMI andalcoholconsumption

Harreby 1996,Denmark98

School children 14 at baseline,25-yearfollow-up

Both 481 Daily smoking vs lessfrequent smoking.Number of cigarettessmoked daily.

Low back pain for morethan 30 days in thepast year

No orminor

No No orminor

No An association betweencurrent smoking andlow back pain in menonly. OR not reported

Unadjusted

Hospitalization due to low back painMattila 2008,

Finland99Adolescents 14-18 at

baseline,14-41 atfollow-up,averagefollow-up11.1 years(0-23 years)

Both 57408 Daily smoking vs not daily Low back painhospitalization

No orminor

Minor No orminor

No OR 1.4 (1.1-1.7) Age, sex, familycomposition,sports activities,timing of puberty,number of healthcomplaints,drinking andschool success

ns � nonsignificant; OR � odds ratio; BMI � body mass index; CI � confidence interval; RR � relative risk.

87.e35Shiri

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Associationbetw

eenSm

okingand

LowBack

Pain