Evidence that the prevalence of childhood overweight is plateauing: data from nine countries

International Journal of Pediatric Obesity, 2011; Early Online, 1–19

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REVIEW ARTICLE

Evidence that the prevalence of childhood overweight is plateauing: data from nine countries

TIM OLDS 1 , CAROL MAHER 1 , SHI ZUMIN 2,3 , SANDRINE P É NEAU 4 , SANDRINE LIORET 5 , KATIA CASTETBON 6 , BELLISLE 4 , JEROEN DE WILDE 7 , MAEA HOHEPA 8 , RALPH MADDISON 9 , LAUREN LISSNER 10 , AGNETA SJ Ö BERG 10 , MICHAEL ZIMMERMANN 11 , ISABELLE AEBERLI 11,12 , CYNTHIA OGDEN 13 , KATHERINE FLEGAL 13 & CAROLYN SUMMERBELL 14

1 Health and Use of Time Group , Sansom Institute , University of South Australia , Adelaide , Australia ; 2 Jiangsu Provincial Center for Disease Control and Prevention , Nanjing , Jiangsu Province 210009 , China ; 3 School of Medicine , University of Adelaide , Adelaide , Australia ; 4 Unit é de Recherche en Epid é miologie Nutritionnelle , Bobigny , France ; 5 French Food Safety Agency, Dietary Survey Unit – Nutritional Epidemiology , Maisons-Alfort , France ; 6 French Institute for Health Surveillance ( InVS ), Universit é Paris 13 , Unit é de surveillance et d ’ é pid é miologie nutritionnelle , Bobigny , France ; 7 Municipal Health Service The Hague , Department of Epidemiology , Department of School Health Care , The Netherlands ; 8 Sport and Recreation New Zealand , Wellington , New Zealand ; 9 Clinical Trials Research Unit , Auckland University , Auckland , New Zealand ; 10 Department of Public Health and Community Medicine, Public Health Epidemiology Unit , Sahlgrenska Academy , University of Gothenburg , Gothenburg , Sweden ; 11 Laboratory for Human Nutrition , Institute of Food , Nutrition and Health , ETH Zurich , Switzerland ; 12 Clinic for Endocrinology , Diabetes and Clinical Nutrition , University Hospital Z ü rich , Switzerland ; 13 Centers for Disease Control and Prevention , Hyattsville , Maryland , USA ; 14 John Snow College , School of Medicine & Health , the Wolfson Research Institute , Stockton , UK

Abstract Until quite recently, there has been a widespread belief in the popular media and scientifi c literature that the prevalence of childhood obesity is rapidly increasing. However, high quality evidence has emerged from several countries suggesting that the rise in the prevalence has slowed appreciably, or even plateaued. This review brings together such data from nine countries (Australia, China, England, France, Netherlands, New Zealand, Sweden, Switzerland and USA), with data from 467,294 children aged 2 – 19 years. The mean unweighted rate of change in prevalence of overweight and obesity was � 0.00 (0.49)% per year across all age � sex groups and all countries between 1995 and 2008. For overweight alone, the fi gure was � 0.01 (0.56)%, and for obesity alone � 0.01 (0.24)%. Rates of change differed by sex, age, socioeconomic status and ethnicity. While the prevalence of overweight and obesity appears to be stabilizing at different levels in different countries, it remains high, and a signifi cant public health issue. Possible reasons for the apparent fl attening are hypothesised.

Key words: Child , adolescent , obesity , overweight , prevalence , international

Background

Paediatric obesity has been described as the primary childhood health problem in developed nations (1), having been linked to many serious physical, social and psychological consequences. These include increased risk of cardiovascular dysfunction (2), type 2 diabetes (3), and pulmonary (4), hepatic (5), renal (6) and musculoskeletal (7) complications; lower

Correspondence: Dr Carol Maher, Post Doctoral Research Fellow, Health and USouth Australia, 5001, Australia. Tel: � 61 8 8302 6558. E-mail: carol.maher@u

(Received 22 November 2010; fi nal version received 8 June 2011 )

ISSN Print 1747-7166 ISSN Online 1747-7174 © 2011 Informa HealthcareDOI: 10.3109/17477166.2011.605895

health-related quality of life (8); negative emotional states such as sadness, loneliness, and nervousness, and increased likelihood of engagement in high-risk behaviours (9); and undesirable stereotyping includ-ing perceptions of poor health, academic and social ineptness, poor hygiene and laziness (10).

There is widespread belief in the popular media that the prevalence of childhood obesity is escalating,

se of Time Group, University of South Australia, GPO Box 2471, Adelaide, nisa.edu.au.

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with ominous predictions about rapidly increasing rates in future decades. For example,

(The British Heart Foundation) claims that more than two thirds of British children will be overweight by 2050 and that Britain as a whole is heading for an obesity epidemic. … At this rate, … more than two thirds of all British kids will suffer from obesity by 2050. (11) Research indicates that if childhood obesity rates continue to soar, half of all Australian chil-dren will be overweight by the year 2025. (12)

These beliefs are echoed in the scientifi c health lit-erature, where it has become commonplace for child-hood obesity to be described as an epidemic or even a pandemic:

... there is growing interest in developing effective public health interventions to address the obesity pandemic. (13) The world-wide gravity of this health crisis is refl ected in data from a number of countries. The global trend of increasing childhood obe-sity makes this a health issue of concern to nurses throughout the world … Crisis level has been reached in a number of European coun-tries … (14)

While there is irrefutable evidence of historical increases in prevalence in recent decades, and strong evidence that prevalence continues to rise in certain countries and particular subgroups, evidence for con-tinuing rises is not universal. In contrast, high quality evidence from several countries around the world is emerging suggesting that the rise in the prevalence of childhood obesity has slowed appreciably, or even plateaued, which will be outlined in this paper.

The purpose of this paper is to show that high quality data from around the world suggest a slowing in the rate of rise of childhood obesity, in at least several countries. There is often great resistance to this idea. Reviewers treat studies suggesting a slow-down with some scepticism, public health experts may feel it will blunt the urgency of their message, and the media are aware that bad news sells better than good (15). Here we assemble evidence from Australia, China, England, France, The Netherlands, New Zealand, Sweden, Switzerland and the USA showing fl attening trends in childhood overweight and obesity.

Methods

This collaborative paper was instigated by the Aus-tralian co-authors (TO and CM). Other researchers

who had recently published or presented data indi-cating slowing or stabilization in the rate of child-hood obesity were identifi ed from literature auto-alerts and personal contacts. Contact details for these researchers were identifi ed either from the ‘ corre-sponding author ’ contact details published with their manuscript, or using an internet search engine. Rel-evant researchers were then sent an introductory email explaining the scope of the paper and inviting them to contribute. In this email, the researchers were also asked to identify any other research teams which they were aware of that were conducting research in the area. Any such additional researchers were then sent the introductory email.

All contacted authors accepted the request to be involved in the manuscript and were invited to ask co-authors from their country if they considered it appropriate to do so. Authors were asked to review recent evidence from their country regarding preva-lence trends in childhood overweight and obesity. Descriptive data from each of the countries are pre-sented in the following sections Australia to the USA, in alphabetical order. With the exception of one French dataset (INCA 1) all height and mass were measured, rather than self-reported. Summary details of the sampling frames and protocols of the various included studies are provided in Appendix 1. Data from all countries were compi ed in Figure 1 and Table I using the International Obesity Task Force (IOTF) cut-offs (16) to allow cross-country com-parisons. Based on the IOTF centile curves for child BMI scores, throughout this manuscript, the term ‘ overweight including obesity ’ (OWOB) corresponds to an adult BMI � 25 kg/m 2 , ‘ overweight excluding obe-sity ’ (OW) corresponds to an adult BMI � 25 kg/m 2 and � 30 kg/m 2 , and ‘ obese ’ (OB) corresponds to an adult BMI � 30 kg/m 2 . The yearly rate of change in the prevalence of obesity (OB), overweight excluding obesity (OW) and/or overweight including obesity (OWOB) was calculated using linear regression. Visual inspection of the data in Figure 1 supports this functional form.

Results

Australia

In Australia, there have been offi cial national surveys of children ’ s weight status in 1985, 1995 and 2007. In addition, there have been many studies conducted at the national, state and regional level in the inter-vening years. A systematic review (17) located 41 Australian surveys of childhood weight status con-ducted between 1985 and 2008. The studies included data on 264,905 Australians aged 2 – 18 years, with raw data available on 70,758 children.

Pleateauing prevalence of childhood overweight 3

5-6 y

7-9 y10-11 y

14-15 y

6-10 y

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1015202530354045

Stockholm

Gothenburg KarlstadUmeå

VästeråsYstad

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Dutch

Turkish

Moroccan

Surinamese

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1995 2000 2005 2010Year of measurement

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USA

Sweden 10-11 y

Netherlands 3-16 y

England 2-15y

China 12-14y

Australia 2-18y

Switzerland 6-13y

NZ 5-14y

France

% overweight or obese % overweight or obese

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Figure 1. The prevalence of overweight and obesity in each country from 1995 – 2008. The broken line represents the mean rate of overweight including obesity for the entire sample (i.e., all countries across all years combined).

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Prevalence estimates for overweight and obese (IOTF criteria) were calculated for each study in age � sex categories, adjusted for age and sex, and plotted against measurement year. Where raw data were available, BMI z-scores (UK 1990 reference) (18) were plotted against measurement year. Two-linear-segment models were used to assess secular trends in prevalence estimates and BMI z-scores. The breakpoint for the two-linear-segment model (derived using the D max method) (19) was 1996. The slopes of linear segments pre- and post-1996 within age, gender and weight-status categories were compared using the method of Zar (20).

There has been a signifi cant deceleration in prev-alence in the years 1996 – 2008. The estimated preva-lence of overweight including obesity in boys rose from 10.2% in 1985 to 21.6% in 1996, to 23.7% in 2008. In girls, the estimated prevalence rose from 11.6% in 1985 to 24.3% in 1996, to 24.8% in 2008. The prevalence of overweight including obesity increased over the period 1985 – 1996 in boys at the rate of � 1.03 (95% CI: 0.69 – 1.37)% per annum, and in girls at the rate of � 1.16 (0.72 – 1.60)% per annum. However, from 1996 onwards, there was no signifi cant increase in prevalence in boys [ � 0.18 (CI: � 0.04 – 0.40)% per annum] or in girls [ � 0.04 ( � 0.20 – 0.28)% per annum]. There were similar trends in standardized BMI (z-scores). In boys, mean BMI z-score increased at the rate of � 0.28 (0.20 – 0.36) units per decade between 1985 and 1996, but slowed to � 0.04 ( � 0.02 – 0.10) units per decade between 1996 and 2008. In girls, it increased at the rate of � 0.33 (0.25 – 0.41) units per decade between 1985 and 1996, but only at � 0.07 ( � 0.01 – 0.15) units per decade between 1996 and 2008. These pat-terns were fairly consistent across the age span. Within each weight-status category, average BMI did not increase in the 1996 – 2008 period. Based on these data, the prevalence of overweight and obesity appears to have fl attened in Australia between 1996 and 2008.

China – Jiangsu Province

In China, under-nutrition was a major health concern prior to the 1980s. However, with economic develop-ment there has been a concurrent rapid change in the nutritional status of Chinese adolescents. Data from national nutrition surveys conducted in 1982, 1992 and 2002 show that the prevalence of overweight and obesity (IOTF c iteria) among adolescents aged 7 – 17 years rose from 1.3% in 1982 to 4.4% and 5.2%, respectively, in 1992 and 2002 (21).

More recent Chinese data concerning prevalence trends are available from two cross-sectional surveys of 824 and 1663 students conducted in the same

eight schools in 2002 and 2007, in Jiangsu Province (22). The province is one of the most affl uent prov-inces in China with a population of 76.2 million. The study locations included Zhenjiang, an affl uent pre-fecture, and Xuzhou, a relatively poor prefecture. In each, schools were randomly selected from each of four different areas: the inner city, a suburb of a city, a regional capital and a town. The age range of the study population was 12 – 14 years.

In total, 15.2% and 15.0% of the students were overweight or obese in 2002 and 2007, respectively (with no signifi cant difference; p � 0.90). Between 2002 and 2007, the increases in height and weight were � 2.1 cm ( p 0.001) and � 1.7 kg ( p � 0.01) in boys; the corresponding fi gures were � 0.7 cm ( p � 0.07) and � 0.3 ( p � 0.56) kg in girls. The sta-bility in the prevalence of overweight and obesity between 2002 and 2007 was observed in both urban and rural areas.

England

Prevalence of childhood obesity in England is rela-tively high in comparison to international reports (23), thus tackling the issue is a Government priority (24). In England, childhood obesity prevalence is monitored annually through two national surveys: the Health Survey for England (25) and the National Child Measurement Programme (26).

The Health Survey for England has measured the height and weight of 49,723 children aged 2 – 15 years, as part of a wider health survey, from a general population sample since 1995 (25). Annual trend data demonstrate an increase in the prevalence of childhood overweight and obesity over the entire 13 years of measurement. However, prevalence of obe-sity, and overweight including obesity appeared to peak around 2005 at 7.4% and 26.4%, respectively, and since appears to have levelled off. A similar lev-elling off trend has been reported for children aged 2 – 10 years and 11 – 18 years using the same Health Survey for England data (27).

The National Child Measurement Programme (26) was established in 2005, and annually weighs and measures the majority of school children in Reception (ages 4 – 5 years) and Year 6 (ages 10 – 11 years) across England. The programme, one of the largest of its kind, informs local planning and deliv-ery of services for children, and provides population-level surveillance data. In 2007/08, approximately 88% (973,073) of all eligible school children were measured. Due to low participation rates in the fi rst year (2005/06) of measurement and improvements in data quality over the early years of the programme, it is not yet possible to carry out detailed trend analyses. However, preliminary analyses comparing prevalence


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data from the last three years (2006/07 and 2007/08) suggest no change (28). These data also demonstrate that obesity prevalence varies signifi cantly across the different regions of England and is higher in urban areas, and in children from deprived backgrounds and certain ethnic minorities including Black and Asian populations (29).

France

In France, numerous studies examining childhood weight status have been conducted in recent years. School-based studies carried out on a triennial basis with children aged 5 – 6 years, 10 – 11 years and 14 – 15 years (Triennial cycle of school surveys; Ministry of Health, Ministry of National Education, National Institute for Health Surveillance) (Direction de la Recherche des Etudes de l ’ Evaluation et des Statis-tiques) (30). Representative sampling is used, and the studies are based on compara le protocols, though the geographical coverage has not been strictly iden-tical from year to year . In 5 – 6-year-old children, the prevalence of overweight including obesity was stable between 1999 and 2000 ( n � 29,896) and 2005 – 2006 ( n � 22,143): 14.4% and 12.1%; as well as the prevalence of obesity: 3.9% and 3.1%, respectively. Similarly, in 10 – 11-year-olds, the prevalence of over-weight including obesity was stable between 2001 and 2002 ( n � 7851) and 2004 – 2005 ( n � 7255): 19.9% and 19.7%; as well as that of obesity: 4.1% and 3.7%, respectively. Finally, a stable prevalence was also observed in 14 – 15-year-old children between 2000 and 2001 ( n � 6590) and 2003 – 2004 ( n � 7229) for overweight including obesity: 15.7% and 16.8%; and obesity: 3.3% and 4.4%.

Another cross-sectional study based on the Euro-pean Childhood Obesity Group protocol (31) was carried out in 2000 ( n � 1582) and repeated in 2007 ( n � 1014) with 7 – 9-year-old children (32). Results showed that the prevalence of overweight including obesity was stable between 2000 (18.1% including 3.8% obesity) and 2007 (15.8%, including 2.8% obesity) (difference not signifi cant).

In addition to these data, yearly prevalence has been provided at a regional level (central/western part of France), in a standardized 6- to 15-year-old popu-lation between 1996 and 2006 (sample size across years � 26,600) (33). According to these data, the stabilization of overweight and obesity prevalence had already occurred in 1998 in most groups studied, and from 2001 in the disadvantaged SES group.

Two further national cross-sectional dietary sur-veys (Etudes Individuelles Nationales sur les Con-sommations Alimentaires, INCA1 and INCA2) (34), allow comparison of overweight rates in two repre-sentative samples of French children aged 3 – 14 y:

INCA 1 (1998 – 99, n � 1017) and INCA 2 (2006 – 07, n � 1030) (34). Weight and height were self-re-ported in INCA 1 and measured objectively in INCA 2. Socio-economic status (SES) was recorded on the basis of parent-reported occupation. In total, 14.5% of the children were overweight (including obesity) in 2006 – 07, which was not signifi cantly different from the 15.2% recorded in 1998 – 99. A strong inverse socio-economic gradient of overweight (including obesity) in French children was observed in both studies. Thus, after an increase in childhood overweight and obesity prevalence in the late 1990s, data from numerous cross-sectional studies con-ducted with French children suggest that rates are currently stabilizing.

The Netherlands – The Hague

Prevalence of overweight and obesity in children in The Netherlands has been among the lowest in Europe (35). Despite this however, prevalence rates have increased signifi cantly since the 1980s. The Fourth Dutch National Growth Study of 1997 showed an overweight prevalence including obesity of 13%, which is at least a two-fold increase since the Third National Growth Study of 1980 (36). Further increases were observed in 2002 – 2003 with cross-sectional data of several regions in The Netherlands showing prevalence rates for overweight including obesity in Dutch children, irrespective of ethnicity, of 14.5% in boys, and 17.5% in girls (37). When ethnicity is taken into account, however, the fi gures change.

An analysis over the years 1999 – 2007 in the city of The Hague shows the fi rst indications of a stabi-lization and even a decrease in certain ethnic groups. The study was based on a series of cross-sectional growth measurements in 3 – 16-year-old children that had been routinely collected by Child Health Care Services of the city of The Hague (37). In Dutch girls, a 14% decline in overweight e cluding obesity was found from 12.6% in 1999 to 10.9% in 2007. This decline was found to be due to a decrease of overweight excluding obesity in 3 – 6-year-olds girls. Age-specifi c analyses in Dutch boys showed a similar signifi cant decrease in 3 – 6-year-olds. Surinamese South Asian (15.0%) and Moroccan (23.0%) chil-dren, and Dutch boys (11.3%) showed an overall stabilization of overweight including obesity preva-lence between 1999 and 2007. There was however a strong and signifi cant increase in overweight includ-ing obesity prevalence in Turkish boys, from 22.4% (1999) to 34.5% (2007), and in Turkish girls, from 27.4 – 33.8%. Despite this unexplained increase of overweight including obesity in Turkish children, the prevalence of overweight including obesity in the

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other ethnic groups seems to have levelled off or even decreased.

New Zealand

In New Zealand, trend analysis has been conducted by comparing anthropometric data of children (aged 5 – 14 years) from two nationally representative sur-veys; the 2002 National Children ’ s Nutrition Survey (38) and the 2006/07 New Zealand Health Survey (39). Both surveys had a similar sample size of approximately 3,200 children and used identical stan-dardized methods to collect height and weight data.

These age-standardized data suggest there has been no change in the prevalence of childhood over-weight and obesity between 2002 (28.8%) and 2006/07 (28.5%). This pattern of stability was found for both boys (2002: 26.1%; 2006/07: 28.2%) and girls (2002: 31.7%; 2006/07: 28.8%) and for M a ori (2002: 38.8%; 2006/07: 37.3%) and Pacifi c Island (2002: 60.0%; 2006/07 57.2%) children; two ethnic groups that display signifi cantly higher rates of over-weight and obesity. Mean BMI among children also remained steady at 19.1 kg/m 2 in 2006/07. For Pacifi c children, however, a signifi cant decline in mean BMI of 2.2kg/m 2 was reported (39). Over a short time frame spanning 2002 – 2006/07, available evidence indicates that the prevalence of childhood overweight and obesity in New Zealand has remained stable.

Sweden

The World Health Organization MONICA Project (a 10-year survey monitoring trends and determi-nants in cardiovascular disease) showed Sweden to be a country with relatively low prevalence of obesity (40). However, Sweden has documented increasing rates of both adult and childhood obesity since the 1980s (41,42).

Recent trends in Swedish childhood obesity and overweight prevalence may be estimated on the basis of school health records from 10 – 11-year-olds. While there is presently no nationwide representative Swed-ish database on childhood obesity, most fourth-grad-ers undergo standardized health examinations by specialized nurses in the school setting.

In earlier studies from Gothenburg, 10-year-old children were examined in 1984 and 2000, and com-parisons of these two cohorts revealed two-fold increases in overweight including obesity and 3- to 4-fold increases in obesity alone. In boys, overweight including obesity increased from 7.2 – 17.1%, and in girls from 8.6 – 19.6% – corresponding increases for obesity were from 0.7 – 2.9% and from 0.8 – 3.0% among boys and girls, respectively (42 – 44). However, these trends did not continue into the 21st century.

In 2004, a new cohort of fourth-graders from Gothenburg was examined (44). Compared to the previously described cohort measured in 2000, prev-alence of overweight including obesity in girls decreased from 19.6 – 15.9% ( p � 0.01); no signifi -cant changes were observed in boys (total n � 8876 in both cohorts).

Similarly, in Stockholm, a total of 4,599 10 – 11-year-old schoolchildren were sampled from dif-ferent socioeconomic districts in academic years starting 1999 and 2003 (45). Obesity prevalence during this time appeare stable, with non-signifi cant decreases from 4.4 – 2.8% in girls, and non-signifi cant increases from 3.2 – 3.8% in boys.

Prevalence estimates from other areas representing various geographical regions of Sweden have recently been reported (Karlstad and Ume å , n � 3,111; and V ä ster å s and Ystad, n � 4473), and likewise sug-gested no change between 2003 and 2005 (46). Despite the overall stability in these four municipal-ities combined, increasing as well as decreasing trends could be observed within the individual municipalities.

Trends in childhood obesity according to SES were considered in the Gothenburg and Stockholm studies, with SES evaluated at the residential area level (44,45). Both of these studies confi rmed that overweight and obesity were more common in chil-dren from less advantaged environments. Among girls in both studies, the decreasing trends were con-sistent in all socioeconomic groups. However, in Stockholm the gap in obesity between boys from lower and higher socioeconomic groups appeared to be widening over time (45). In Gothenburg, increas-ing trends in overweight including obesity tended to occuring boys from middle-income areas, in contrast to decreasing trends in both high and low-income areas (44).

In summary, no signifi cant increases in overweight or obesity have been observed in recent studies of Swedish schoolchildren in six municipalities (47). The synthesized studies offer a consistent picture of stabilizing obesity rates particularly in urban Sweden, with some evidence that the trend is reversing in girls but not in boys.

Switzerland

A national study of 6 – 13-year-olds in Switzerland in 2002 ( n � 2431) suggested nearly 1 in 5 schoolchil-dren were overweight (48). In order to assess trends in Swiss childhood obesity, a 5-year follow-up study was carried out in 2007 with 2,222 6 – 13-year-old children (49). In both studies, a national representa-tive sample was obtained (48,49) and overweight and obesity were determined on the basis of Centres for


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Disease Control and Prevention (CDC) BMI references (50). However, for the purposes of this review, IOTF cut-offs are used, and CDC cut-offs are provided in Appendix 2.

In 2007, the prevalence of overweight excluding obesity and obesity in boys were 11.4% and 2.3%, respectively, and in girls they were 11.2% and 2.1%. Compared to 2002, there were decreases in the prev-alence of overweight (excluding obesity) in girls ( � 4.2%) and boys ( � 1.4%) and obesity in both gen-ders ( � 1.6% in boys and � 1.6% in girls). In 2002, there were neither geographic nor demographic dif-ferences in prevalence rates. In contrast, in 2007 the prevalence of obesity was signifi cantly higher in com-munities with a population � 100,000 compared to smaller communities ( p � 0.05) and some regional differences were observed (please refer to [49] for further details).

Two other studies similarly provide evidence of recent stabilization in obesity and overweight preva-lence in Swiss children. In the canton of Geneva, there has been a small (not statistically signifi cant) decrease in the overweight and obesity prevalence in 5 – 6-year-old children from 2003 – 2008 (51). Also, a Swiss national study on iodine nutrition in 6 – 12-year-old children, which measured weight and height as a sec-ondary outcome measure, found stabilization in the prevalence of obesity between 2002 and 2009 (52). In summary, over the past 5 years, the prevalence of obe-sity has stabilized or decreased in Swiss children.

USA

Trend analyses in the USA are based on data from the National Health and Nutrition Examination Surveys (NHANES). NHANES is a cross-sectional survey, designed to monitor the health and nutritional status of the US civilian, non-institutionalized population (CDC/NCH ; National Health and Nutrition Exami-nation Survey 2009) (53). Starting in 1999 the survey became continuous with release and reporting of data every two years. The survey involves nationally repre-sentative samples, selected using a complex, multistage probability sample design. Oversampling is used to obtain reliable estimates of health and nutritional mea-sures for certain population subgroups. Sample weights account for differential probabilities of selection, non-response and non-coverage. Data are grouped into two-year cycles (1999 – 2000, 2001 – 2002, 2003 – 2004, 2005 – 2006 and 2007 – 2008). For the purpose of this review paper, analyses have been undertaken using IOTF defi nitions of obesity and overweight (16) rather than the usual CDC defi nitions.

Tests for trends between 1999 – 2000 and 2007 – 2008 were carried out using sex-specifi c logistic regression models adjusted for age and race-ethnicity.

Because previous analyses (54) have shown signifi -cant differences in prevalence of obesity by age and between non-Hispanic whites, non-Hispanic blacks and Mexican Americans in the USA, trend tests were adjusted for age group and race-ethnic group.

In analyses, survey period (1999 – 2000, 2001 – 2002, 2003 – 2004, 2005 – 2006 and 2007 – 2008) was treated as a continuous variable. All analyses were done with sample weights and were performed using the statistical packages SAS version 9.1 (SAS Insti-tute, Cary, NC, USA) and SUDAAN version 9.0 (RTI, Research Triangle Park, NC, USA) to account for the complex sample design.

In 2007 – 2008, 34.3% (SE 1.3) of children and adolescents 2 – 19 years of age were overweight (including obesity) while 15.7% (SE 1.0) were obese. In the same period, 15.7% (SE 1.1) of boys and 15.8% (SE 1.2) of girls were obese. Signifi cant age and race/ethnic differences in obesity prevalences exist (55). In 2007 – 2008, 2 – 5-year-old children were less likely to be obese compared to older children. In addition, sex specifi c analyses indicated that non-Hispanic black girls were more likely to be obese compared to non-Hispanic white girls and Mexican American boys were more likely to be obese com-pared to non-Hispanic white boys (54).

Trend tests showed no signifi cant trend in over-weight or obesity between 1999 – 2000 and 2007 – 08 among either boys ( p � 0.742 and p � 0.152) or girls ( p � 0.095 and p � 0.203) after adjusting for age and race-ethnicity. It appears that the rapid increase in obesity prevalence seen in the US during the 1980s and 1990s has slowed, especially among girls, during the most recent decade.

Aggregated data

Data from all the countries are compiled in Table I, and trends in summary prevalence data from each country are presented visually in Figure 1. Where available, data are presented in age, sex and weight status subgroups. All data were based upon objec-tively measured height and weight, with the excep-tion of the French INCA1 study, which obtained self-reported data for its 1,017 participants.

Linear regression was used to determine the annual rate of change in prevalence of obesity, over-weight including obesity and overweight excluding obesity, in each subgroup from each country. Overall, the mean (SD) unweighted rate of change in the prevalence of child and adolescent overweight and obesity (taking averages across all ethnicities for the Dutch data) from 112 reports (country specifi c age � sex categories) was � 0.00 (0.49)% per year. The mean rate of change in 40 reports of overweight including obesity combined was � 0.01 (0.58)% per

8 T. Olds et al .

Tab

le I

. P

reva

lenc

e of

ove

rwei

ght

and

obes

ity

in c

hild

ren

and

adol

esce

nts

in n

ine

coun

trie

s be

twee

n 19

95 a

nd 2

008.

Cou

ntry

Stu

dyA

geS

exS

ampl

e si

ze1

Wei

ght

stat

us19

9519

9619

9719

9819

9920

0020

0120

0220

0320

0420

0520

0620

0720

08S

lope

2

Aus

tral

ia(1

7)2–

18B

oys

1343

47O

W16

.218

.40.

182–

18B

oys

OB

5.4

5.3

–0.0

12–

18B

oys

OW

OB

21.6

23.7

0.18

2–18

Gir

ls13

0558

OW

18.6

18.9

0.02

2–18

Gir

lsO

B5.

75.

90.

022–

18G

irls

OW

OB

24.3

24.8

0.04

Chi

na(2

2)12

–14

Boy

s12

82O

WO

B19

.319

.0–0

.06

12–1

4G

irls

1205

OW

OB

10.7

10.7

0.00

Eng

land

(25)

& u

npub

lishe

d an

alys

is (

Din

sdal

e)2–

15B

oth

4972

3O

W15

.314

.915

.316

.717

.215

.718

.018

.318

.820

.119

.017

.717

.80.

33

2–15

Bot

hO

B3.

84.

64.

44.

25.

75.

25.

26.

55.

96.

77.

46.

06.

30.

24

2–15

Bot

hO

WO

B19

.119

.519

.720

.922

.920

.923

.224

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.826

.423

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57F

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e(3

0)5–

6B

oys

5203

93O

W8.

77.

6–0

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5–6

Boy

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B3.

62.

9–0

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5–6

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sO

WO

B12

.310

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.30

5–6

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lsO

W12

.210

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.28

5–6

Gir

lsO

B4.

33.

3–0

.17

5–6

Gir

lsO

WO

B16

.513

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.45

(32)

7–9

Boy

s25

963

OW

14.0

11.3

–0.3

97–

9B

oys

OB

3.9

2.8

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67–

9B

oys

OW

OB

17.9

14.1

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irls

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14.7

14.9

0.03

7–9

Gir

lsO

B3.

62.

8–0

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7–9

Gir

lsO

WO

B18

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(30)

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1B

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1507

63O

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.60.

0310

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Boy

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B4.

03.

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OW

OB

19.5

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310

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lsO

W16

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.50.

1310

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lsO

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23.

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.10

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1G

irls

OW

OB

20.3

20.4

0.03

(30)

14–1

5B

oys

1381

93O

W12

.812

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.03

14–1

5B

oys

OB

3.5

4.8

0.43

14–1

5B

oys

OW

OB

16.3

17.5

0.40

14–1

5G

irls

OW

12.1

12.1

0.00

14–1

5G

irls

OB

3.2

3.9

0.23

14–1

5G

irls

OW

OB

15.3

16.0

0.23

INC

A 1

and

IN

CA

2

(34)

3–6

Bot

h56

0O

W9.

910

.50.

08

3–6

Bot

hO

B6.

33.

0–0

.41

(Con

tinue

d)

Int J

Ped

iatr

Obe

s D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y E

mm

a G

raha

m o

n 09

/07/

11Fo

r pe

rson

al u

se o

nly.


Cou

ntry

Stu

dyA

geS

exS

ampl

e si

ze1

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ght

stat

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9519

9619

9719

9819

9920

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0120

0220

0320

0420

0520

0620

0720

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lope

2

3–6

Bot

hO

WO

B16

.313

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.35

7–10

Bot

h64

4O

W14

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.43

7–10

Bot

hO

B3.

03.

50.

067–

10B

oth

OW

OB

17.5

14.6

–0.3

611

–14

Bot

h76

8O

W10

.413

.10.

3411

–14

Bot

hO

B1.

22.

10.

1111

–14

Bot

hO

WO

B11

.715

.20.

44(6

5)6–

15B

oth

2660

0 O

WO

B10

.513

.615

.614

.715

.515

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.813

.515

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.714

.00.

13N

ethe

rlan

ds(3

7)3–

16B

oys

2558

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87.

78.

89.

88.

59.

69.

09.

38.

90.

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gin

3–16

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22.

42.

12.

42.

52.

52.

62.

52.

3

3–16

Boy

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WO

B11

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.110

.912

.211

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.20.

113–

16G

irls

2480

5O

W12

.612

.612

.111

.911

.611

.511

.211

.110

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lsO

B3.

73.

93.

43.

93.

32.

93.

13.

23.

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3–16

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WO

B16

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.515

.515

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.414

.314

.314

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.31

Tur

kish

or

igin

3–16

Boy

s73

50O

W14

.516

.314

.815

.716

.318

.217

.321

.321

.40.

84

3–16

Boy

sO

B7.

96.

98.

29.

811

.59.

910

.810

.813

.10.

633–

16B

oys

OW

OB

22.4

23.2

23.0

25.4

27.8

28.1

28.1

32.1

34.5

1.47

3–16

Gir

ls68

21O

W19

.418

.619

.117

.819

.520

.918

.622

.523

.20.

483–

16G

irls

OB

8.0

8.2

7.4

8.9

8.2

7.7

8.5

10.2

10.7

0.30

3–16

Gir

lsO

WO

B27

.426

.826

.526

.727

.728

.627

.232

.733

.80.

78M

oroc

can

orig

in3–

16B

oys

5452

OW

12.1

13.1

14.2

14.4

13.8

11.9

11.0

15.0

16.7

0.25

3–16

Boy

sO

B5.

66.

56.

84.

64.

75.

57.

55.

67.

20.

103–

16B

oys

OW

OB

17.8

19.6

21.0

19.0

18.6

17.4

18.5

20.6

23.9

0.35

3–16

Gir

ls55

45O

W20

.120

.214

.918

.815

.021

.018

.023

.220

.50.

323–

16G

irls

OB

7.2

9.1

7.6

6.3

6.7

6.9

5.8

7.2

6.6

–0.1

93–

16G

irls

OW

OB

27.3

29.3

22.4

25.0

21.7

27.9

23.8

30.3

27.1

0.13

Sur

inam

ese

Sou

th A

sian

3–16

Boy

s49

76O

W8.

96.

18.

97.

97.

410

.610

.410

.614

.50.

69

3–16

Boy

sO

B5.

15.

56.

25.

15.

45.

14.

15.

75.

4–0

.04

3–16

Boy

sO

WO

B14

.011

.615

.113

.012

.915

.714

.516

.319

.90.

653–

16G

irls

4697

OW

9.3

12.7

11.1

13.1

10.2

10.8

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10.0

12.6

0.08

3–16

Gir

lsO

B4.

43.

84.

13.

63.

93.

02.

14.

54.

5–0

.04

3–16

Gir

lsO

WO

B13

.716

.515

.216

.614

.213

.814

.314

.617

.10.

06A

ll et

hnic

itie

s co

mbi

ned

3–16

Boy

s43

366

OW

10.1

9.8

10.6

11.1

10.3

11.5

10.7

12.1

13.0

0.32

3–16

Boy

sO

B3.

84.

14.

34.

24.

64.

54.

74.

55.

40.

153–

16B

oys

OW

OB

13.9

13.9

14.9

15.3

14.8

15.9

15.4

16.6

18.4

0.46

3–16

Gir

ls41

868

OW

14.1

14.7

13.6

13.8

13.1

14.3

13.3

14.4

14.7

0.02

Tab

le I

. (C

onti

nued

).

(Con

tinue

d)

Int J

Ped

iatr

Obe

s D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y E

mm

a G

raha

m o

n 09

/07/

11Fo

r pe

rson

al u

se o

nly.

10 T. Olds et al .

Cou

ntry

Stu

dyA

geS

exS

ampl

e si

ze1

Wei

ght

stat

us19

9519

9619

9719

9819

9920

0020

0120

0220

0320

0420

0520

0620

0720

08S

lope

2

3–16

Gir

lsO

B4.

85.

34.

84.

94.

64.

34.

25.

05.

2–0

.02

3–16

Gir

lsO

WO

B18

.920

.018

.318

.717

.718

.617

.519

.419

.80.

00N

ew Z

eala

nd(3

8) a

nd (

39)

5–14

Boy

s64

923

OW

18.0

20.1

0.42

5–14

Boy

sO

B8.

18.

10.

00A

ll et

hnic

itie

s co

mbi

ned

5–14

Boy

sO

WO

B26

.128

.20.

42

5–14

Gir

lsO

W21

.720

.1–0

.32

5–14

Gir

lsO

B10

.08.

7–0

.26

5–14

Gir

lsO

WO

B31

.728

.8–0

.58

Mao

ri o

rigi

n45–

14B

oth

OW

24.4

24.6

0.04

5–14

Bot

hO

B14

.412

.7–0

.34

5–14

Bot

hO

WO

B38

.837

.3–0

.30

Pac

ifi c

orig

in4

5–14

Bot

hO

W32

.731

.0–0

.34

5–14

Bot

hO

B27

.326

.2–0

.22

5–14

Bot

hO

WO

B60

57.2

–0.5

6S

wed

en(4

5)10

–11

Boy

s23

19O

W18

.416

.7–0

.43

Sto

ckho

lm10

–11

Boy

sO

B3.

23.

80.

1510

–11

Boy

sO

WO

B21

.620

.5–0

.28

10–1

1G

irls

2260

OW

17.7

16.4

–0.3

310

–11

Gir

lsO

B4.

42.

8–0

.40

10–1

1G

irls

OW

OB

22.1

19.2

–0.7

3G

othe

nbur

g(4

4)10

–11

Boy

s44

40O

W14

.214

.80.

1510

–11

Boy

sO

B2.

92.

8–0

.03

10–1

1B

oys

OW

OB

17.1

17.6

0.13

10–1

1G

irls

4436

OW

16.6

13.4

–0.0

810

–11

Gir

lsO

B3.

02.

5–0

.13

10–1

1G

irls

OW

OB

19.6

15.9

–0.9

3K

arls

tad

(46)

10–1

1B

oth

1637

OW

15.1

17.5

2.40

10–1

1B

oth

OB

2.7

2.4

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010

–11

Bot

hO

WO

B17

.819

.92.

10U

meå

(46)

10–1

1B

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1474

OW

18.3

18.1

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Bot

hO

B2.

32.

70.

4010

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hO

WO

B20

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.80.

20V

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(46)

10–1

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oth

2379

OW

18.0

19.4

0.70

10–1

1B

oth

OB

5.3

4.7

–0.3

010

–11

Bot

hO

WO

B23

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.10.

40Y

stad

(46)

10–1

1B

oth

584

OW

18.5

15.8

–1.3

510

–11

Bot

hO

B4.

84.

7–0

.05

10–1

1B

oth

OW

OB

23.3

20.5

–1.4

0S

wit

zerl

and

(48,

49)

6–13

Boy

s22

52O

W12

.811

.4–0

.28

Tab

le I

. (C

onti

nued

).

(Con

tinue

d)

Int J

Ped

iatr

Obe

s D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y E

mm

a G

raha

m o

n 09

/07/

11Fo

r pe

rson

al u

se o

nly.


Cou

ntry

Stu

dyA

geS

exS

ampl

e si

ze1

Wei

ght

stat

us19

9519

9619

9719

9819

9920

0020

0120

0220

0320

0420

0520

0620

0720

08S

lope

2

6–13

Boy

sO

B3.

92.

3–0

.32

6–13

Boy

sO

WO

B16

.713

.7–0

.60

6–13

Gir

ls23

74O

W15

.411

.2–0

.84

6–13

Gir

lsO

B3.

72.

1–0

.32

6–13

Gir

lsO

WO

B19

.113

.3–1

.16

US

A(5

3) &

unp

ublis

hed

anal

yses

2–19

Boy

s10

024

OW

18.4

16.3

20.3

17.4

18.5

0.07

2–19

Boy

sO

B12

.514

.515

.713

.615

.70.

282–

19B

oys

OW

OB

30.9

30.8

36.0

31.0

34.2

0.34

2–19

Gir

ls97

03O

W15

.517

.419

.916

.718

.50.

182–

19G

irls

OB

15.1

15.1

15.7

14.8

15.8

0.06

2–19

Gir

lsO

WO

B30

.632

.535

.631

.534

.30.

322–

5B

oys

OW

10.4

8.4

12.2

11.0

10.1

0.10

2–5

Boy

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B3.

44.

46.

84.

44.

40.

102–

5B

oys

OW

OB

13.8

12.8

19.0

15.4

14.5

0.20

2–5

Gir

lsO

W8.

910

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.610

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.00.

222–

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OB

6.9

7.2

5.6

6.8

5.0

–0.2

12–

5G

irls

OW

OB

15.8

17.4

21.2

17.3

17.0

0.12

6–11

Boy

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W19

.016

.120

.017

.415

.9–0

.16

6–11

Boy

sO

B17

.718

.820

.316

.924

.20.

566–

11B

oys

OW

OB

36.7

34.9

40.3

34.3

40.1

0.31

6–11

Gir

lsO

W15

.320

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.515

.218

.90.

086–

11G

irls

OB

20.7

20.5

22.0

17.6

22.4

0.03

6–11

Gir

lsO

WO

B36

.040

.645

.532

.841

.30.

1412

–19

Boy

sO

W21

.819

.424

.120

.124

.30.

1912

–19

Boy

sO

B12

.714

.916

.215

.415

.40.

3012

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Boy

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WO

B34

.534

.340

.335

.539

.70.

5812

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Gir

lsO

W19

.018

.719

.220

.721

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2312

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Gir

lsO

B14

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.616

.416

.20.

2212

–19

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lsO

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B33

.933

.334

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.70.

57

OB

, obes

e; O

W,

over

wei

ght

(excl

udin

g o

bes

e);

OW

OB

, ov

erw

eight

(incl

udin

g o

bes

e);

Sam

ple

siz

e sh

ows

the

com

bin

ed s

ample

siz

es o

f th

e dif

fere

nt

surv

eys

in e

ach c

ountr

y f

rom

all

yea

rs c

om

bin

ed;

2L

inea

r re

gres

sion

was

use

d to

defi

ne

slop

e (s

ee M

etho

ds);

3S

ampl

e si

ze f

or b

oth

sexe

s co

mbi

ned;

4S

ampl

e si

ze f

or e

thni

c su

bgro

ups

not

avai

labl

e.

Tab

le I

. (C

onti

nued

).

Int J

Ped

iatr

Obe

s D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y E

mm

a G

raha

m o

n 09

/07/

11Fo

r pe

rson

al u

se o

nly.

12 T. Olds et al .

Int J

Ped

iatr

Obe

s D

ownl

oade

d fr

om in

form

ahea

lthca

re.c

om b

y E

mm

a G

raha

m o

n 09

/07/

11Fo

r pe

rson

al u

se o

nly.

year across all age � sex groups and all countries between 1995 and 2008. For overweight excluding obe-sity, the fi gure was 0.01 (0.56)% for 36 reports, and for obesity alone � 0.01 (0.24) for 36 reports. Overall, 50 of 112 reports (45%) showed declines, 60 (53%) showed increases and two (2%) showed no change.

When split by sex, the fl attening was more marked for girls than for boys. For overweight including obe-sity (taking average across all ethnicities for the Dutch data), the mean (SD) rate of change for boys (15 reports) was � 0.07 (0.37)% per year, while for girls (15 reports) it was � 0.16 (0.49)% per year. For obe-sity alone, the mean rate of change for boys was � 0.08 (0.25)% per year (14 reports), while for girls it was � 0.08 (0.19)% per year (14 reports). There were also differences by age, with the fl attening being more marked in younger children. The mean rate of change in overweight including obesity for preschoolers (age 2 – 5 or 6) was � 0.11 (0.29)% per year (six reports), compared to � 0.09 (0.69)% per year for primary school aged children (6 – 11 or 12 years; 17 reports) and � 0.25 (0.25)% per year for adolescents (12 – 19 years; nine reports). The corresponding fi gures for obesity alone were – 0.14 (0.17)% per year for pre-schoolers (6 reports), � 0.02 (0.26)% per year for primary school age (15 reports), and � 0.26 (0.11)% per year for adolescents (six reports).

Discussion

Main fi ndings

While this paper was not designed as a systematic review or meta-analysis of trends in the prevalence of childhood overweight and obesity, it does bring together data from nine countries showing a slowing plateau, and in some cases a decline in the prevalence of child-hood obesity and overweight in several countries in recent years. The countries involved in this paper rep-resent numerous regions around the globe including Western Europe, North America, Asia and Oceania. In addition, this trend for slowing or plateauing does not appear to be isolated to the countries reported in this paper. Recent studies from Russia (56), Greenland (57) and Scotland (58) have reported similar trends. In addi-tion, a major US Surveillance System based on low income children has also shown a stabilization in obe-sity levels (59). Thus it appears that there are many regions in the world where childhood obesity is not, as has been suggested, increasing exponentially, but is rather showing stabilizing trends.

Strengths and limitations

It is important to acknowledge the strengths and weaknesses of the current review. This paper is the

fi rst to bring together recent data from several coun-tries reporting stabilization in the rates of childhood obesity and/or overweight. In all cases, data arose from large, population-based studies, involving a total of over 500,000 children from nine countries. All the studies, with one exception (the INCA 1 data from France) used measured height and weight. In view of the fact the INCA 1 data provided baselines for trend analysis, and self-reported data usually underestimate BMI (60), it is likely that the data still support a stabilizing trend. The methodologies adopted in the different studies varied considerably in terms of the sampling frame, numbers of partici-pants, geographical spread of participants (in some cases representing entire nations, and in several cases representing specifi c geographical regions within countries) and parameters measured (e.g., some studies considered SES and ethnicity while most did not). In two countries, data came from geographi-cally narrow areas (Jiangsu Province for the China section, and The Hague for The Netherlands section) thus it is unclear whether the trends for stabilization in obesity rates reported in this paper are representa-tive of their entire nation. Calculation of average rates of change do not take into account varying sample sizes or the fact subgroup analyses within a country may be more alike than analyses across countries. In this study it was possible to overcome a seemingly trivial problem in the literature – the failure of some authors to specify if ‘ overweight ’ includes obesity or not. All of the authors contribut-ing to the present review have used the combined defi nition as defi ned by Cole et al. (16).

We quantifi ed trends in childhood overweight and obesity using BMI as a metric, rather than other measures of adiposity, such as skinfolds, because weight status is defi ned on the basis of BMI catego-ries by international convention (16), and there are very few comprehensive datasets available using skin-folds. One meta-analysis (61) found consistent increases in the skinfold thicknesses of children in the years up until 2004, a time we would expect BMIs to be plateauing (on the basis of the current paper). In the same study, Olds (61) showed there has been a shift towards central accumulation of body fat. So it is possible that children may be becoming fatter at the same BMI.

While the presentation of data from all countries according to IOTF cut-offs allows for valuable cross-country comparison, it also has limitations. Some countries routinely use alternative methods for defi n-ing overweight and obesity [for example, in England, they are usually defi ned on the basis of the UK1990 BMI growth reference (18), and in Switzerland and the US they are defi ned on the basis of CDC 2000 growth charts (62). Zimmermann and colleagues


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(48) compared the sensitivity of CDC and IOTF defi nitions of overweight and obesity, and found that in Swiss children, the CDC defi nitions had superior ability over IOTF defi nitions to detect obesity determined on the basis of percentage body fat from skinfold tests. Furthermore, while the pat-terns of stabilization are similar across the nine countries, this study is not intended as a compre-hensive global survey of recent changes in chil-dren ’ s weight status. There are very likely countries where the prevalence of paediatric overweight and obesity is still increasing.

Different rates of change among subgroups

It is important to note that there are exceptions to this pattern for stabilization in particular subgroups of the pediatric population. In this review, data showed that rates of change at times differed accord-ing to sex, age, SES and ethnicity. For example, the trend for stabilization was more marked in girls than in boys. This was apparent in both aggregated data and data from New Zealand. Aggregated data also showed more marked stabilization in younger than in older children, which was also evident in the French, US and Australian data. In addition, the English and the French surveys reported differences according to socioeconomic status. In France, there was an increase in overweight prevalence in children with ‘ blue collar ’ parents, while there was a decrease in prevalence of overweight in children with ‘ white collar ’ parents (30).

In urban Sweden, decreasing prevalence in female obesity was observed across all socio-economic groups, whereas amongst Swedish boys decreases occurred consistently within the affl uent group, with inconsistent trends for lower and middle income groups. Variations on the basis of ethnicity were also reported in some cases. In The Netherlands, over-weight including obesity rates declined in children of Dutch origin between 1999 and 2007, but rose dramatically over the same period in children from Turkish backgrounds.

Stabilization at different prevalence levels

It is interesting to note that while stabilization appears to be occurring across the nine countries highlighted in this study, prevalence is not stabilizing at the same level. For roughly comparable age ranges (mid-points of range from 9 – 15 years), the average prevalence of overweight including obesity across the time periods reported ranges from 13.5% in France to 37.4% in the USA. The reasons for this are unclear; however, a combination of genetic and cultural factors s likely to be involved. While it is tempting to suggest that

initiatives aimed at preventing childhood obesity have been more successful at kerbing the increase in prevalence in certain countries than in others, this conclusion should be made with caution. It is equally possible that efforts across countries may be equally well designed, but are starting at a different base level. It may be that in countries with already high prevalence rates, it is easier to ‘ pick the low-hanging fruit ’ , that is to reduce overweight or obesity in chil-dren who are already substantially overweight or already obese. It could equally be argued that it may be harder to reverse trends in countries with already high prevalence. At the very least, the phenomenon of stabilization at different prevalences suggests that whatever the cause, factors in the social and physical environment probably play a role.

Potential causes

The intervention hypothesis

There are a number of possible reasons for the sta-bilization in childhood overweight and/or obesity rates. Childhood obesity has been recognized as a major public health concern in many countries for several years now, prompting public health cam-paigns and interventions aimed at promoting healthy eating and increased physical activity. It may be that the cumulative effect of such programs is now result-ing in stabilization of the prevalence of overweight and obesity in children.

Offering some support to the intervention hypoth-esis are dietary data collected in the French INCA surveys. These data showed that average energy intake in 3 – 14-year-old French children signifi cantly decreased from 1910 kcal/d in 1999 to 1739 kcal/d in 2006 – 07 ( p � 0.0001) (34). The link between this decrease in energy intake and the stabilization of overweight and obesity in the past decade deserves further investigation.

In particular, there have been numerous interven-tions aimed at addressing early risk factors of over-weight and obesity, such as birth weight, diet, growth-rates and transition from breast milk and/or formula to solid foods. As each of these factors has been associated with early childhood overweight and obesity (63), it is likely that interventions addressing them have contributed to the current trend towards stabilization of prevalence.

The saturation equilibrium hypothesis

An alternative explanation for stabilization in obesity rates may be that childhood overweight and/or obe-sity has now reached a point of saturation equilib-rium in many countries. Any given environment

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offers opportunities for children (and adults) to overeat and be inactive. The proportion of overweight children will depend on interactions between the dis-tribution of resilience (for example as a result of naturally high levels of physical activity or some other form of socially-programmed resilience) and the degree of ‘ obesogenicity ’ of the environment. It may be that today we live in societies which have become so obesogenic, which offer so many opportunities for high energy intake and sedentary pastimes, that any child who is predisposed to overweight has become overweight, and the remaining children are resistant to excessive adiposity. Differences in the levels of sta-bilization might refl ect different ‘ in-built ’ levels of resilience.

The self-selection hypothesis

A further explanation may be self-selection bias. While the data presented in this paper arose from major population-based studies in each of the nine countries, we cannot completely rule out sampling bias. It is possible that due to increased public aware-ness of childhood obesity and increased perceived stigmatization more parents of overweight and obese children declined participation in the latter measure-ment years compared to the baseline measurement years on which trend a alyses were based. However, some of the studies cited here are almost censuses of the population of interest, and selection bias is unlikely in these cases. Moreover, the assumption of increasing stigmatization in recent years may be questioned; it could be argued that severe stigmatiza-tion of childhood overweight and obesity has been recognized for many decades and that decreasing stigmatization may have also occurred in recent years due to high prevalences changing norms.

Conclusions

It is unclear whether the stabilization trends outlined in the countries in this paper presage a long-term change in the rates of childhood overweight and obe-sity, or whether it is a temporary lull, and overweight and obesity rates will soon begin to rise again. Future prevalence depends on many factors including immi-gration patterns, prevalence within age cohorts, and socio-demographic shifts. The fact that the stabiliza-tion of prevalence appears to be more marked in younger cohorts suggests that we might see a ‘ wash-through ’ effect as these groups age, with future decreases in prevalence. However, the experience of the inaccurate British forecasts [in which dire forecasts for the rates of overweight in 2 – 11-year-old girls in 2020 needed to be downgraded from 34% to 17%,

and the rate of obesity in 12 – 19-year-old girls revised from 30% to 9% (64)] should serve as a warning that projections should be treated with extreme caution.

Above all, the data presented in this paper should not be interpreted as meaning that childhood over-weight and obesity are not important public health issues. While rates of overweight and obesity appear to be stabilizing at present in many countries, they are still unacceptably high, with signifi cant ramifi ca-tions for the health and well-being of these children as they age. Moreover, the rates may still be increas-ing in some countries. Furthermore, it is possible that the ‘ adiposity gap ’ between the rich and poor in devel-oping countries is widening. If so, narrowcast inter-ventions targeting high-risk subgroups may be both more equitable and cost-effective than population-level broadcast interventions.

Acknowledgements

The authors would like to thank Marie-Fran ç oise Rolland-Cachera, for her contribution to the French descriptive section; Louisa Ells, Cathy Mulhall, Hywell Dinsdale and Carolyn Summerbell, for contributing the English data and description; and the Swedish Council for Social Research and Working Life, who were a major contributor to the Swedish work.

Declaration of interest : The authors report no confl icts of interest. The authors alone are respon-sible for the content and writing of the paper.

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Appendix 1. Summary details of the sampling frames and protocols of the included studies.

Study Sampling frame Sampling exclusions Training of measurers Equipment calibrated Data weighting

Australia Variable, as meta analysis of 41 studies

Variable, as meta-analysis of 41 studies

Variable Unknown Variable

China – (Shi, Lien et al.

2005) (22)

Cluster, regional, same 8 schools in 2002, 2007

No Measured by trained health workers in local CDC

Yes No

England (The NHS Information Centre for Health and Social Care 2010) (25)

multi-stage stratifi ed probability

sampling design

Those living in institutions

Training and practical on interview and anthropometric measures

Yes Yes (to account for non-response), by age, gender, household type, number of children in household and geographic region

France – Triennial cycle of school surveys (Minst é re de al Sant é 2008) (30).

Two-stage random national sampling

No exclusions among children able to attend schools

Detailed instructions provided (nurses and physicians)

No Yes, by age, gender, regions, type of schools (education priority areas; public/private schools)

European Childhood Obesity Group protocol (Salanave, P é neau et al. 2009) (32)

Random national sampling

No exclusions among 7 – 9 years children who were able to attend schools

Detailed instructions provided (nurses and physicians)

No Yes, by age, gender, administrative school district, type of schools (education priority area, size of class by level)

INCA 1 The sample was made representative of the French population diversity through stratifi cation (region of residence, agglomeration size) and use of the quota method (age, gender, household size, head of household socioprofessional status)

Severely disabled and lack of literacy in French (caregiver)

One-day training on the questionnaires

Not applicable None

INCA 2 (Lioret, Touvier et

al. 2009) (34)

Random national Severely disabled and lack of literacy in French (caregiver)

One-day training for anthropometrics and questionnaires

No Yes, by unequal sampling probabilities and for differential non-responses by region, agglomeration size, age, gender, occupation of the head of household, size of the household, and season of the year

(P é neau, Salanave et al. 2009)

All children attending a regional health examination center

No exclusion among examined children at the center

Nurses trained when recruited

Scale: yes Height gauge: no

(fi xed)

Yes, by age, gender, economic status (deprived/non deprived)

(Continued)

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18 T. Olds et al .

Appendix 1. (Continued).


The Netherlands (de Wilde, van

Dommelen et al. 2009) (37)

Random, local City of the Hague,

routine health assessments of all children

None Youth Health Care professionals have been trained for several years

Yes No, analyses adjusted for age and/or gender

New Zealand (Ministry of Health

2003) (38)

Two staged sampling frame. A random sample of schools was selected, then children were randomly selected within these schools

Schools on the Chatham Islands, correspondence schools, and schools with less than 50 students, (note: all Te Kura Kaupapa schools were included regardless of size).

Fee-paying foreign students or foreign students on Ministry of Foreign Affairs and Trade scholarships were excluded

Anthropometric measurement training provided with interviewers tested before going into the fi eld

Yes Yes, by age, gender, ethnicity and region

(New Zealand Ministry of Health 2008)

(39)

Multi-stage, stratifi ed, probability proportionate to size (PPS) sample design, with increased sampling of some ethnic groups

Meshblocks with a very small number of households, and off-shore islands

Anthropometric measurement training provided with interviewers tested before going into the fi eld

Yes Yes, by age, gender, District Health Board area and ethnic group

Sweden – Stockholm (Sundblom, Petzold et al. 2008) (45)

8 SES areas, 10 schools from

each randomly selected

Very small schools Trained school nurses No Yes, by gender and place of residence

Gothenburg (Sj ö berg, Lissner et al. 2008)

� 80% coverage of population

None Trained school nurses Yes No

Karlstad (Lager, Fossum et al. 2009) (46)

94% coverage of population


Ume å (Lager, Fossum et al. 2009) (46)

66 – 92% coverage of population


V ä ster å s (Lager, Fossum et al. 2009) (46)


None Trained school nurses No No

Ystad (Lager, Fossum et al. 2009) (46)


None Trained school nur es Yes No

Switzerland – (Zimmermann, G ü beli et al. 2004) (48)

Random, national, probability-proportionate-to-size cluster sampling

None Individual training (2 examiners)

Yes No (PPS design instead of data weighting)

(Continued)

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Appendix 1. (Continued).


(Aeberli, Ammann et al. 2009) (49)

Random, national, probability-proportionate-to-size cluster sampling

None Individual training (2 examiners)

Yes No (PPS design instead of data weighting)

USA (Centres for Disease Control and Prevention 2008)

(53)

NHANES uses a complex, multistage, probability sampling design to select a representative sample of the resident civilian non-institutionalized population, including non-citizens

The sample does not include persons residing in nursing homes, members of the armed forces, institutionalized persons, or US nationals living abroad

NHANES staff are trained to follow standardized examination protocols, to calibrate equipment according to a prescribed schedule and method, and to measure and record the survey data with precision. Additionally, retraining sessions, gold standard examinations performed by expert examiners, and fi eld observations are conducted on a regular basis to reinforce the importance of measurement precision and standardized data collection methodology

Yes Yes, weights are created in NHANES to account for the complex survey design (including oversampling), survey non-response, and post-stratifi cation

Appendix 2 . Overweight and obesity prevalences in Swiss schoolchildren from two national studies conducted 2002 and 2007, reported according to Centers for Disease Control and Prevention (CDC) references.

Overweight % (SD) Obese % (SD) Overweight � obese % (SD)

2007 1 Boys ( n � 1083) 11.3 (0.94) 2 5.4 (0.67) 3 16.7 (1.1) 3 Girls ( n � 1139) 9.9 (0.87) 3 3.2 (0.52) 3 13.1 (0.98) 3

2002 1 Boys ( n � 1169) 12.5 (0.96) 7.4 (0.8) 19.9 (1.2)Girls ( n � 1235) 13.2 (0.96) 5.7 (0.7) 18.9 (1.1)

1 2007 and 2002: National study to determine the prevalence of overweight and obesity in schoolchildren in Switzerland (64,65); 2 in percentage (standard error), all such values; 3 signifi cantly different from 2002 ( p � 0.05).

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Evidence that the prevalence of childhood overweight is plateauing: data from nine countries

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