(2007) 157–162www.elsevier.com/locate/ypmed

Preventive Medicine 45

Trends and socioeconomic differences in overweight among physicallyactive and inactive Finns in 1978–2002

Katja Borodulin a, Tomi Mäkinen a, Mikael Fogelholm b,c,Marjaana Lahti-Koski d, Ritva Prättälä a,⁎

a National Public Health Institute, Department of Health Promotion and Chronic Disease Prevention, Mannerheimintie 166, FI-00300 Helsinki, Finlandb UKK Institute for Health Promotion Research, Tampere, Finlandc Pirkanmaa Hospital District, Research Unit, Tampere, Finland

d The Finnish Heart Association, Helsinki, Finland

Available online 15 February 2007

Abstract

Objective. The aim was to study the associations of physical activity and socioeconomic status with overweight from 1978 to 2002 and toexplore whether the trend in overweight was different across educational groups or leisure time and commuting physical activity groups.

Method. The study population comprised 37,084 women and 34,191 men who participated in cross-sectional postal surveys carried outannually from 1978 to 2002. The surveys included independent nationally representative random samples of Finns aged 25 to 64 years.Information on weight, height, leisure time and commuting physical activity was self-reported. The level of education was obtained from nationalregister data. Overweight was defined as a body mass index (kg/m2) of 25 or higher.

Results. Overweight was more prevalent among the physically inactive and lower educated. The prevalence of overweight increased over time.Across the study years, those men and women who participated in leisure time or commuting physical activity had a lower prevalence ofoverweight in all educational groups. The increase in the prevalence of overweight followed a similar pattern in all physical activity and educationgroups.

Conclusion. Engagement in physical activity has not prevented an increase in the prevalence of overweight in any socioeconomic group amongFinnish men and women from 1978 to 2002.© 2007 Elsevier Inc. All rights reserved.

Keywords: Physical activity; Overweight; Socioeconomic differences; Trends

Introduction

The increasing prevalence of overweight is a growing publichealth problem (World Health Organization, 2000). The causesof these upward trends in overweight are related to changes inphysical activity and eating habits (Hill et al., 2003; Grundy,1998; Jebb and Moore, 1999). In eastern Finland, physicalactivity at work and during commuting has decreased due tochanges in society such as motorization and mechanization,while physical activity during leisure time has increased(Barengo et al., 2002). Previously, occupational physical activityconstituted a large proportion of daily energy expenditure. In

⁎ Corresponding author. Fax: +358 9 4744 8338.E-mail address: ritva.prattala@ktl.fi (R. Prättälä).

0091-7435/$ - see front matter © 2007 Elsevier Inc. All rights reserved.doi:10.1016/j.ypmed.2007.02.007

order to prevent weight gain, the decreased energy expenditureshould be counterbalanced by increasing physical activityduring leisure time or by decreasing energy intake. In Finland,the increase in leisure time physical activity (Barengo et al.,2002) has not been high enough to offset the decreased levels ofoccupational physical activity (Fogelholm et al., 1996).

There is a need to understand the social determinants of aphysically active lifestyle. It has been suggested that socio-economic status affects health through health behaviors such assmoking, eating and physical activity (Macintyre, 1997;Laaksonen et al., 2003; Lakka et al., 1996; Lynch et al., 1997;Miech et al., 2006). Follow-up studies have described socio-economic differences in the development of obesity; theymainlysuggest a higher prevalence of obesity in lower social classes(Ball et al., 2002; Droyvold et al., 2004; Martikainen andMarmot, 1999; Rissanen et al., 1991). Moreover, these

Table 1The characteristics of the study population

Women(n=37,084)

Men(n=34,191)

n % n %

Age group25–36 12,144 33 11,506 3437–48 11,929 32 11,234 3349–64 13,011 35 11,454 34

BMIBMI <25 23,128 62 15,948 47BMI ≥25 13,956 38 18,246 53

EducationHigher 10,028 27 8696 25Medium 12,351 33 11,611 34Lower 14,705 40 13,887 41

Study period1978–1982 8440 23 9037 261983–1987 6496 18 5723 171988–1992 7804 21 6976 201993–1997 7360 20 6374 191998–2002 6984 19 6084 18

Leisure time physical activityActive (2 times/week or more) 18,866 51 16,616 49Inactive (once a week or less) 18,218 49 17,578 51

Commuting physical activityActive (daily) 19,762 43 23,001 33Inactive 17,322 53 11,193 67

Finland, 1978–2002, cross-sectional population-based data. Only 25–64-year-old respondents with no missing information in study variables were included.

158 K. Borodulin et al. / Preventive Medicine 45 (2007) 157–162

socioeconomic differences in health have increased in recentyears (Mackenbach et al., 2003). To understand the increasingprevalence of overweight and its socioeconomic and behavioralbackground it is important to determine whether socioeconomicgroups have different time trends in the prevalence of over-weight compared with their level of physical activity.

Few studies have investigated the population trends ofoverweight or obesity in socio-demographic and physicalactivity groups (Lahti-Koski et al., 2000; Lindstrom et al.,2003; Miech et al., 2006; Lahti-Koski et al., 2002) and evenfewer studies have simultaneously investigated trends ofoverweight, socioeconomic status and physical activity (Miechet al., 2006). The aim of this study was to study the trends from1978 to 2002 in the associations between physical activity andsocioeconomic status and overweight among adult Finns and toexplore whether the trend in overweight was different acrosseducational groups or leisure time and commuting physicalactivity groups.

Material and methods

The cross-sectional population-based data were obtained from the ‘HealthBehaviour and Health among Finnish Adult Population’ survey of the NationalPublic Health Institute. A postal questionnaire has been sent to a random sampleof Finns aged 15 to 64 years annually since 1978. Data from the years 1978–2002 and from respondents aged 25 to 64 years were included in this study. Thedata sets from 1978 to 2002 were pooled into five periods: 1978–1982, 1983–1987, 1988–1992, 1993–1997, and 1998–2002. The response rates to thesurveys have ranged from 65% to 84%. Generally, women have had slightlyhigher response rates than men throughout the entire study period and the overallresponse rate has decreased since the late 1970s (Tolonen et al., 2006). Therespondents with missing information on any of the variables used in the furtheranalyses were excluded. The sample therefore comprised 37,084 women and34,191 men. Before the respondents with missing information were excluded,the initial n for women was 60,735 and for men 62,444.

The data were self-reported, including information on weight, height, leisuretime and commuting physical activity. Body mass index was calculated fromheight and weight (kg/m2) and a cut-off point of 25 was used to defineoverweight. A cut-off point of 30 gave results similar to those of 25. Leisure timephysical activity was assessed with the following question: “In your leisure time,how often do you take physical exercise for at least 30 min, which makes you atleast moderately out of breath and causes you to perspire?” The response optionswere the following: daily, 2–3 times a week, once a week, 2–3 times a month, afew times a year or less and I cannot exercise because of an illness or disability.Those exercising two or more times per week were categorized as physicallyactive and the others as inactive. Commuting physical activity was measuredwith the following question: “Howmany minutes a day do you spend walking orriding a bicycle to and from work?” The response options were the following: Ido not work or I work at home, I go to work by car, less than 15 min a day, 15–30 min a day, 30–60 min a day and more than an hour a day. Those engaging inany (even less than 15 min a day) commuting physical activity were categorizedas active and the others as inactive. The respondents who did not work outsidethe home were classified as inactive.

Leisure time and commuting physical activity were split into active andinactive groups because the goal was to analyze 25-year trends. More preciseclassification was not possible because the formulations of the questions onphysical activity were slightly modified over the study years. This must be takeninto account when interpreting the results.

Information on education was obtained from the Population Registermaintained by Statistics Finland and linked with the survey data using personalidentification codes. The information from the Register is valid and has fewermissing values than the self-reports. Three educational groups were formed:higher, comprising respondents with a university or graduate school degree;middle, with respondents having vocational training and upper secondary school

education; and lower, with respondents having basic education or for whommissing information on schooling was lacking.

Statistical methods

The data were analyzed using the SAS package (1999 SAS Institute Inc.,Cary, NC, USA). Cross-tabulation was used to study the time trends in theprevalence of overweight by categories of physical activity and educationallevel. Logistic regression analysis, as presented with odds ratios (OR) and 95%confidence intervals (95% CI), was conducted to investigate the cross-sectionalassociation of overweight with education, study period, leisure time andcommuting physical activity. First, age-adjusted models were producedseparately for each independent variable to study their independent effect onoverweight (model 1). Second, multivariate logistic regression analyses wereperformed in which the independent variables were added to the models one at atime (models 2 to 4). All models were age-adjusted. Two-way interactions weretested separately in each study period to determine whether the probability ofbeing overweight was different across the study periods when stratified byeducation and physical activity. All analyses were performed separately for menand women.

Results

The characteristics of the respondents are described in Table1. The trends in overweight are demonstrated across educationallevels separately for leisure time (Figs. 1 and 2) and commuting(Figs. 3 and 4) physical activity. During the 25-year studyperiod there was a consistent difference in the prevalence ofoverweight both between the educational groups and betweenthe active and inactive respondents. Persons engaging in leisuretime physical activity had a lower prevalence of overweight ateach level of education (Figs. 1 and 2). Similarly for commuting

Fig. 3. The age-adjusted prevalence of overweight (body mass index ≥25) infive-year periods from 1978 to 2002 by education and commuting physicalactivity in Finnish women.

Fig. 1. The age-adjusted prevalence of overweight (body mass index ≥25) infive-year periods from 1978 to 2002 by education and leisure time physicalactivity in Finnish women.

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physical activity, the prevalence of overweight remainedsystematically lower among the physically active (Figs. 3 and4). The prevalence of overweight was highest among those withlower education who were physically inactive during leisuretime or commuting throughout the study periods.

In age-adjusted model 1 for women (Table 2) and men (Table3), the ORs of being overweight were higher among those withlower education and the physically inactive. Compared with thestudy period 1978–1982, the prevalence of overweight washigher in study periods 1993–2002 in women and 1983–2002in men. The inclusion of education, study period and leisuretime and commuting physical activity in the multivariatemodels did not markedly modify the associations with theprevalence of overweight. In the final model for men andwomen, the prevalence of overweight was higher in the studyyears 1988–2002 than in the reference period of 1978–1987.Compared with active women and men with ORs of 1.00, theORs for leisure time and commuting physical activity were 1.24(1.18–1.30) and 1.35 (1.29–1.41) in inactive women, respec-tively, and 1.19 (1.14–1.25) and 1.19 (1.13–1.25) in inactivemen, respectively.

Differences in the ORs between the subgroups were slightlylarger in women than in men (Tables 2 and 3), suggesting larger

Fig. 2. The age-adjusted prevalence of overweight (body mass index ≥25) infive-year periods from 1978 to 2002 by education and leisure time physicalactivity in Finnish men.

differences among women in the prevalence of overweightacross educational and physical activity groups. Interaction testswere mainly non-significant between education and the twotypes of physical activity across the study periods. Thisindicates that the increasing prevalence of overweight hasfollowed a similar pattern in all physical activity and edu-cational groups over time. The gender difference and theconsistent increase in the prevalence of overweight can also beseen in Figs. 1–4.

Discussion

These extensive data on Finnish men and women suggestthat overweight was more prevalent among the physicallyinactive and those with lower education from 1978 to 2002.Overweight became more prevalent towards the end of theperiod. Those men and women who participated in leisure timeor commuting physical activity had a consistently lowerprevalence of overweight in all educational groups over thestudy period. The increase in the prevalence of overweightfollowed a similar pattern in all physical activity and educationgroups.

Fig. 4. The age-adjusted prevalence of overweight (body mass index ≥25) infive-year periods from 1978 to 2002 by education and commuting physicalactivity in Finnish men.

Table 2The associations of educational level, research period, leisure time physical activity and commuting physical activity with the prevalence of overweight (body massindex ≥25) in women, as presented with odds ratios (OR) and 95% confidence intervals (CI)

Model 1a Model 2: educationand study period

Model 3: model2+ leisure timephysical activity

Model 4: model3+commutingphysical activity

OR CI OR CI OR CI OR CI

EducationHigher 1.00 1.00 1.00 1.00Medium 1.60 1.51–1.70 1.63 1.53–1.74 1.64 1.54–1.74 1.62 1.52–1.72Lower 1.86 1.76–1.97 2.05 1.93–2.18 2.06 1.93–1.18 2.01 1.89–2.13

Study period1978–1982 1.00 1.00 1.00 1.001983–1987 0.97 0.90–1.04 1.02 0.95–1.09 1.02 0.95–1.10 1.02 0.95–1.091988–1992 0.99 0.92–1.05 1.07 1.00–1.15 1.09 1.02–1.17 1.08 1.01–1.151993–1997 1.17 1.09–1.23 1.35 1.26–1.45 1.40 1.31–1.51 1.37 1.27–1.471998–2002 1.15 1.07–1.23 1.39 1.30–1.50 1.45 1.35–1.57 1.42 1.32–1.53

Leisure time physical activityActive (two times/week or more) 1.00 1.00 1.00Inactive (once a week or less) 1.17 1.12–1.45 1.22 1.16–1.27 1.24 1.18–1.30

Commuting physical activityActive (daily) 1.00 1.00Inactive 1.39 1.33–1.45 1.35 1.29–1.41

All models were age-adjusted. Finland, 1978–2002.a Age-adjusted logistic regression analysis was performed separately for education, study period, leisure time and commuting physical activity for their

independent association with overweight.

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Intervention studies have shown that increased regularphysical activity leads to weight reduction and weightmaintenance (Andersen et al., 1999; Ross and Janssen, 2001).Most follow-up studies and systematic reviews have reportedthat physical activity is related to less weight gain (Di Pietro etal., 2004; Haapanen et al., 1997; Fogelholm and Kukkonen-Harjula, 2000; Hill and Wyatt, 2005; Jebb and Moore, 1999),

Table 3The associations of educational level, research period, leisure time physical activityindex ≥25) in men, as presented with odds ratios (OR) and 95% confidence interva

Model 1a Model 2and stud

OR CI OR

EducationHigher 1.00 1.00Medium 1.16 1.09–1.23 1.15Lower 1.25 1.18–1.32 1.34

Study period1978–1982 1.00 1.001983–1987 1.07 1.00–1.14 1.081988–1992 1.14 1.07–1.22 1.181993–1997 1.26 1.18–1.34 1.321998–2002 1.34 1.25–1.43 1.43

Leisure time activityActive (two times/week or more) 1.00Inactive (once a week or less) 1.17 1.12–1.22

Commuting physical activityActive (daily) 1.00Inactive 1.23 1.18–1.29

All models were age-adjusted. Finland, 1978–2002.a Age-adjusted logistic regression analysis was performed separately for educ

independent association with overweight.

although controversial results according to which physicalactivity has non-significant association with future weight statusare reported as well (Fogelholm and Kukkonen-Harjula, 2000;Bak et al., 2004; Petersen et al., 2004).

One Finnish study reported increasing trends in obesity,inverse associations of obesity with education and physicalactivity and a larger increase of obesity over time among

and commuting physical activity with the prevalence of overweight (body massls (CI)

: educationy period

Model 3: model2+ leisure timephysical activity

Model 4: model3+commutingphysical activity

CI OR CI OR CI

1.00 1.001.09–1.22 1.14 1.08–1.21 1.14 1.07–1.201.26–1.42 1.32 1.25–1.40 1.31 1.23–1.39

1.00 1.001.01–1.16 1.09 1.02–1.17 1.08 1.00–1.151.11–1.26 1.19 1.12–1.27 1.17 1.09–1.251.24–1.42 1.36 1.27–1.45 1.32 1.24–1.421.34–1.53 1.47 1.37–1.58 1.44 1.34–1.55

1.00 1.001.19 1.14–1.25 1.19 1.14–1.25

1.001.19 1.13–1.25

ation, study period, leisure time and commuting physical activity for their

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physically inactive women (Lahti-Koski et al., 2000, 2002). InSwedish adults, an increasing trend in overweight has beenreported with a lower prevalence of overweight among thephysically active and those with higher education (Lindstrom etal., 2003). One study among adolescents suggested thatoverweight increased at a faster rate in families of lowersocioeconomic status than in the families of higher status andphysically active girls and boys exhibited overweight consis-tently less than inactive ones (Miech et al., 2006).

According to our findings, all educational and physicalactivity groups seemed to have gained weight and the cross-sectional differences have remained the same size over time.Ideally, our findings would have suggested that those who arephysically active did not have an increasing prevalence ofoverweight or they at least demonstrated a slower increase in itsprevalence. By increasing physical activity an individual maylose weight, but on the other hand, overweight individuals maynot regularly engage in physical activity. One follow-up studysuggested that obesity led to physical inactivity, while physicalactivity did not prevent weight gain (Petersen et al., 2004).Physical activity and overweight may therefore have a two-waycausal pathway. It may well be that overweight people find itdifficult to take part in higher intensity activities that wouldconsume more energy.

This study is one of the few that reports trends on overweightover a 25-year-period, with a simultaneous perspective onphysical activity and socioeconomic factors. The study dataenabled investigation of population trends in a representativesample. The weaknesses of this study are related to the self-reported questionnaires. It is likely that some of the respondentsunderestimated their weight or overestimated their height — ageneral problem in self-reports (Bostrom and Diderichsen,1997; Kuczmarski et al., 2001). Unfortunately, no validationdata on this sample are available for further discussion of thetopic. We used a body mass index cut-off point of 25 to classifypersons as overweight and due to underreporting may havemisclassified those with true body mass indices of 25–27 asnormal weight. We carried out additional analyses using a cut-off point of 30 (obesity) and obtained results similar to thosewith a cut-off point of 25. Thus, the associations can hardly becaused by misclassification only.

The questions on physical activity are limited to itsfrequency and duration and give no estimates of energyexpenditure or overall physical activity level. In spite of thefinding that physically active persons had a lower prevalence ofoverweight throughout the study years, the activity level wasnot high enough to entirely prevent an increase in theprevalence of overweight among the physically active group.This may be explained by the weakness of the assessmentmethod as the cut-off point for leisure time physical activity twotimes per week is not enough to prevent weight gain. Previousstudies have recommended as much as 60 to 90 min of dailyphysical activity to prevent weight gain (Saris et al., 2003).Furthermore, our assessment of leisure time physical activitydid not include daily physical activity, i.e. household chores andrunning errands. The increasing trend in overweight despite theincrease in leisure time physical activity may be related to

diminished levels of energy used in everyday tasks at home andwork.

Conclusion

Our findings suggest that the increase in the prevalence ofoverweight has followed a similar pattern in all educational andphysical activity groups from 1978 to 2002, although botheducation and physical activity are related to a lowerprevalence of overweight. From the public health perspective,we still need to conduct research to identify those who do notgain weight and then plan health promotion strategies toprevent the development of overweight. For example, it wouldbe crucial to use accurate assessments of physical activity anddietary habits that would give proper dose–response associa-tions with weight gain. On the other hand, our findings indicatepromising results on socioeconomic variation as the gapbetween high and low socioeconomic groups has not grownsignificantly over time in relation to overweight. However, westill found a strong socioeconomic pattern in overweight,indicating that it is crucial to include the socioeconomic factorin health promotion strategies. The strategies should especiallyimprove the chances of lower socioeconomic groups to engagein physical activity and choose low-energy foods. In practice,this means, for example, better availability of exercise facilitiesand fruit and vegetables in communities of lower socio-economic groups.

Acknowledgments

The funding of the Finnish Ministry of Education, theFinnish National Public Health Institute and the Juho VainioResearch Foundation and the contribution of Kati Vähäsarja,MSc and Kirsi Talala, M.Soc.Sc in the preliminary analyses ofthe data are gratefully acknowledged.

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