Nutritional Epidemiology

Transcription

1 Nutritional Epidemiology Socioeconomic Gradients in Body Weight of German Children Reverse Direction between the Ages of 2 and 6 Years 1 Kristina Langnäse, Mareike Mast, Sandra Danielzik, Carina Spethmann and Manfred J. Müller 2 Institut für Humanernährung und Lebensmittelkunde, Christian-Albrechts-Universität zu Kiel, Kiel, Germany ABSTRACT In Western societies, there is an inverse socioeconomic status (SES) gradient in overweight, but its onset is unknown. It was the aim of this study to assess the onset of the SES gradient in overweight children from birth to age 5 7 y. This was a cross-sectional and longitudinal study of 1326 children [668 boys and 658 girls; median age, 6.3 y; interquartile range (IQR), 0.4 y] in Kiel, northwest Germany. We assessed parental education as an indicator of SES, parental body mass index (BMI) (fathers: median age, 37.0 y; IQR: 8.0 y; mothers: median age, 34.0 y; IQR, 6.5 y), BMI of mothers before pregnancy, and breastfeeding practices. We found a positive SES gradient in birthweight, which was further enhanced by parental overweight. SES gradients in nutritional status disappeared at the age of 1 and 2 y. In contrast, in 5- to 7-y-old children, there was an inverse SES gradient in BMI and overweight, which was further enhanced by parental overweight. We concluded that (i) SES gradients in nutritional state show considerable changes during the first years of life, (ii) the inverse SES gradient in overweight becomes manifest between years 2 and 6 of life and (iii) parental BMI enhances SES gradients in birthweight and BMI at 5 7 y of age. J. Nutr. 133: , KEY WORDS: childhood obesity birthweight socioeconomic state prevention nutritional state 1 This study was supported by grants from the Deutsche Forschungsgemeinschaft (DFG Mü ), Wirtschaftliche Vereinigung Zucker, Bonn, Danone Stiftung, Münschen, PreCon Bickenbach. 2 To whom correspondence should be addressed. mmüller@nutrfoodsc.uni-kiel.de. 3 Abbreviations used: BMI, body mass index; KOPS, Kiel Obesity Prevention Study; SDS, standard deviation score; SES, socioeconomic status. There is a worldwide increase in the prevalence of overweight and obesity (1). Socioeconomic status (SES) 3 has an influence on the manifestation of overweight and obesity. An inverse SES gradient in overweight and obesity is obvious in women (2). Among men and children, the relationship is less consistent (2). We have shown recently that social differences in being overweight are already manifest in a group of 5- to 7-y-old children in northwest Germany (3). In these children, the mean prevalence of overweight is 18.5%. There is an inverse SES gradient, and the highest fat mass is observed in children from a low socioeconomic class (3). The odds ratios of being overweight reach 3.1 in boys and 2.3 in girls, respectively (low versus high social class) (3). Parental overweight exacerbates the relationship between SES and the prevalence of being overweight, with 37.5% (low socioeconomic class) and 22.9% (high socioeconomic class) of children of overweight parents being overweight (3). It has been proposed that differences in body mass index (BMI) by socioeconomic class are formed at least in part during early childhood (4). However, the time of manifestation of SES gradients in overweight is unknown. Contrary to the inverse SES gradient in overweight of 5- to 7-y-old children, others have found a positive SES gradient in birthweight (5,6). There is a positive linear relationship between increasing SES and the proportion of infants weighing 3,500 g (5), and low birthweight occurs more frequently with socioeconomic deprivation (6). There is only preliminary evidence that SES-induced differences in birthweight persist during the first years of life (7). These data suggest that the development of growth and weight is more pronounced in people of higher SES compared with those of middle or lower SES (7). This idea is in line with data from twin studies showing a significant tracking of body size from birth to late adolescence where BMI could be predicted from birthweight and parental BMI (8). Following this idea one would expect a further stabilization of the positive SES gradient in later years that is contrary to the above-mentioned findings of an inverse SES gradient in overweight in 5- to 7-y-old children and adults (2,3). We therefore analyzed the data of the Kiel Obesity Prevention Study (KOPS) cohort (9,10) to assess the onset of the SES gradient in overweight in children from birth to age 5 7 y. In addition we analyzed the effects of SES, parental BMI, birthweight, breastfeeding, and BMI at 1 and 2yoflife on BMI of 5- to 7-y-old children. METHODS Data from the KOPS between 1996 and 1998 were analyzed (9,10). Within this time period school physicians of the city of Kiel (northwest Germany, 248,000 inhabitants) examined a total of 6927 children age 5 7 y. From this population 2561 (37%) children were recruited. The aims of KOPS were explained to all parents and /03 $ American Society for Nutritional Sciences. Manuscript received 24 July Initial review completed 27 August Revision accepted 20 November

2 790 LANGNÄSE ET AL. TABLE 1 Characteristics of the 1,326 study children (age 5 7 y) and their parents1 Group/characteristic All children (n 1,326) Boys (n 668) Girls (n 658) Children Age, y 6.3 ( ) 6.3 ( ) 6.3 ( ) Birthweight, g 3,490 (3,123 3,760) 3,550 (3,150 3,820)a 3,440 (3,100 3,690) BMI, kg/m2 1 y 17.1 ( ) 17.3 ( )a 16.9 ( ) 2 y 16.3 ( ) 16.5 ( )a 16.1 ( ) 5 7 y 15.6 ( ) 15.6 ( ) 15.5 ( ) Prevalence, % High birthweight Overweight3 at 1 y b 15.9 Overweight3 at 2 y b 9.5 Overweight3 at 5 7 y Breastfeeding 0 mo b mo mo Parents Age, y Father 37.0 ( ) 38.0 ( )a 37.0 ( ) Mother 34.0 ( ) 35.0 ( ) 34.0 ( ) Current BMI, kg/m2 Father 24.7 ( ) 24.5 ( )a 24.9 ( ) Mother 22.5 ( ) 22.5 ( ) 22.4 ( ) Prevalence of overweight,4 % Father b 49.1 Mother BMI of mother before pregnancy, kg/m ( ) 21.5 ( ) 21.6 ( ) Prevalence of overweight before pregnancy, % Change5 in BMI of mother, % 3.4 ( ) 3.3 ( ) 3.5 ( ) Parental education level, % Low Middle High Values are median (IQR). a Different from girls, Mann-Whitney U test, P b Different from girls, 2 test, P BMI, body mass index; IQR, interquartile range. 2 Birthweight 4,000 g. 3 Equal to or greater than sex- and age-specific 90th percentile of BMI according to Kromeyer-Hauschild et al. (11). 4 BMI 25.0 kg/m2. 5 BMI before pregnancy minus current BMI. children. Parents and children participated voluntarily, and written consent was obtained from all parents. The local ethical committee of the Christian-Albrechts-University Kiel approved the study protocol. Nutritional status of the children was measured, and sociodemographic and lifestyle factors of the children and families were assessed using a questionnaire. For this study 1326 complete data sets on nutritional status of children and their parents as well as social status were available. This subpopulation was 51.7% of the total KOPS population recruited between 1996 and Anthropometric data (age, gender, body weight and height) suggests that our study population was representative of the total population of 5- to 7-y-old children in Kiel (11). Nutritional status. Birthweight, height and weight of the children at 1 and 2 y were recorded from certificates of preventive medical check-ups. At the age of 5 7 y body weight was measured to the nearest 0.1 kg on a calibrated balance-beam scale with subjects wearing underclothes. Height at 5 7 y was assessed to the nearest 5 mm, and BMI [weight (kg)/height (m 2 )] was calculated. The investigators were instructed every year, and the quality of measurements was regularly controlled. The between- and within-observer imprecision variance was tested every year and was 2.5%. Parental BMI was calculated from self-reported body weight and height. The BMI of mothers before pregnancy was taken from measured values documented on the children s birth certificates. High birthweights were considered as 4,000 g corresponding to a period of wk of pregnancy. Prevalence of overweight in children was defined as equal or above the gender- and age-specific 90th percentiles of BMI according to German reference data (12). In parents, overweight was defined as BMI 25 kg/m 2 (1). Parents were grouped as no overweight parent, as one overweight parent or as two overweight parents. Socioeconomic status. Data on SES were taken from our questionnaire. The highest school education achieved by either mother or father was used to define social class. Parental education was divided into low, middle and high. Low was assigned to those who attended school for 9 y, middle to those who left school after 10 y and high to those who achieved an advanced level of education (13 y). In a previous study this classification was compared with other SES indicators (e.g., size of family, occupational grade of parents) (12). All SES indicators were moderately cross-correlated, but the choice of the indicator did not affect between-group differences. Education was found to be suitable to reflect SES (11). Statistical analysis. The statistical analysis was performed with StatView 4.0 (Abacus Concepts). Results were presented as median and interquartile range. The nonparametric Mann-Whitney U test was used to determine gender differences in nutritional status. The nonparametric Kruskal-Wallis test was performed to analyze nutritional status of the children at birth, 1 y, 2 y and 5 7 y, with respect to different SES of the children as well as different parental nutritional status. After significant differences between groups were identified, a Bonferroni correction was used to identify the location of the differences. The 2 tests compared prevalence of high birthweight, breastfeeding and overweight among groups. To examine changes in nutritional status between birth and the age of 5 7 y,sd scores [SDS as taken from data obtained within a German reference population of

3 SOCIOECONOMIC GRADIENTS IN OVERWEIGHT 791 children (11) using the least-mean-square method based on Cole 13)] were calculated for BMI at birth and at the age of 5 7 y. Medians of BMI were stratified according to SES, parental nutritional status and breastfeeding. Within each group, differences between SDS at birth and SDS at the age of 5 7 y were tested by the Wilcoxon signed rank test. Quartiles of birthweight and BMI at 5 7 y were calculated. Differences among groups were analyzed by the nonparametric Kruskal-Wallis test. The level of significance was set at P RESULTS Characterization of the study population. The study population is characterized in Table 1. There were significant gender differences in birthweight as well as the nutritional status of infants and prepubertal children. Boys had higher birthweight and BMI at the age of 1 and 2 y. Compared with girls, boys were more often overweight at the age of 1 as well as 2 y. Boys were also more frequently not breastfed. In addition, their fathers were older, had a lower BMI and were less often overweight compared with fathers of girls. There were no differences in the actual or prepregnancy weight of mothers of boys and girls. Comparing the nutritional status of mothers before pregnancy with their current nutritional status when their children were 6 y old, 88.8% of mothers who were overweight before pregnancy remained overweight. The corresponding data for normal weight and underweight mothers were 83% and 49.4%, respectively. Only 11.2% of normalweight mothers became overweight during the study period. Of the children, 46.9% were of high SES, whereas 53.1% came from families with middle or low parental education. Sex was not associated with parental education. Influence of parental education on nutritional status. Stratifying nutritional variables according to parental education showed between group differences in age and BMI at the age of 5 7 y(table 2). Children with low parental education were older and had a higher BMI than children with high parental education. There were significant social gradients in the prevalence of high birthweight and breastfeeding (positive gradients for parental education) as well as the prevalence of overweight at the age of 5 7 y (inverse gradient for parental education). No parental education gradient was seen for BMI of children at the age of 1 and 2 y. Parental education was also related to parental BMI (negative gradient). Means for parental BMI and the prevalence of overweight were lowest in parents with high education and highest in parents with low education. There was an inverse parental education gradient in the prevalence of overweight in mothers before pregnancy as well as in their weight gain (current BMI minus BMI before pregnancy). Influence of parental overweight on nutritional variables. There was a close association between parents and children s TABLE 2 Characteristics of 1,326 study children (age 5 7 y) and their parents stratified according to parental education level1 Parental education level Low (n 309) Middle (n 391) High (n 626) Children Age,a y 6.3 ( )b 6.3 ( ) 6.2 ( ) Birthweight, g 3,430 (3,080 3,750) 3,500 (3,100 3,770) 3,500 (3,188 3,760) BMI, kg/m2 1 y 16.9 ( ) 17.2 ( ) 17.1 ( ) 2 y 16.3 ( ) 16.4 ( ) 16.3 ( ) 5 7 ya 15.7 ( )b 15.6 ( ) 15.5 ( ) Prevalence, % High birthweight Overweight3 at 1 y Overweight3 at 2 y Overweight3 at 5 7 yc Breastfeedingc 0 mo mo mo Parents Age, y Fathera 36.0 ( )b 36.0 ( )b 39.0 ( ) Mothera 32.0 ( )bd 33.0 ( )b 36.0 ( ) Current BMI, kg/m2 Fathera 25.7 ( )bd 24.9 ( )b 24.2 ( ) Mothera 23.4 ( )bd 23.1 ( )b 21.9 ( ) Prevalence of overweight,4 % Fatherc Motherc BMI of mother before pregnancy,a kg/m ( )bd 22.1 ( )b 21.1 ( ) Prevalence of overweight before pregnancy,c % Change5 in BMI of mother,a % 5.2 ( ) 3.9 ( ) 2.8 ( ) 1 Values are median (IQR). a Different among groups, Kruskal-Wallis test, P b Different from high parental education level, Bonferroni post hoc test, P c Different among groups, 2 test, P d Different from middle parental education level, Bonferroni post hoc test, P BMI, body mass index; IQR, interquartile range. 2 Birthweight 4,000 g. 3 Equal to or greater than sex- and age-specific 90th percentile of BMI according to Kromeyer-Hauschild et al. (11). 4 BMI 25.0 kg/m2. 5 BMI before pregnancy minus current BMI.

4 792 LANGNÄSE ET AL. BMI. Using parental BMI as a continuous variable, there was a positive association between BMI mothers and BMI children (r 0.289; P 0.001). After categorization (BMI mothers 25 versus 25 kg/m 2 ), r was for normal weight and for overweight and obese mothers, respectively (each P 0.001). Table 3 presents nutritional variables of children and parents stratified according to parental nutritional status. Birthweight, prevalence of high birthweight and BMI at the age of 5 7 y significantly differed between groups of normal and overweight parents. Children of normal weight and underweight parents had lower birthweights compared with the other children. The prevalence of high birthweight was lowest in children of normal-weight parents. By contrast, the highest values were seen in children of two overweight parents. There was a positive gradient between the prevalence of parental overweight and the BMI of children at the age of 5 7 y. Children with two overweight parents had the highest BMI and were more frequently overweight compared with the other groups (Table 3). No significant between-group differences were observed in the prevalence of breastfeeding. Influence of breastfeeding on nutritional variables. With the children stratified according to breastfeeding practices, there were no between-group differences in age, birthweight, BMI or prevalence of overweight at 1, 2 and 5 7 y(table 4). In a comparison of breastfed with nonbreastfed infants in the latter group, mothers had higher current as well as prepregnancy BMI. The prevalence of breastfeeding increased with parental education. Effect of parental education and parental overweight on birthweight and nutritional status of infants and children. Figure 1 shows the effect of parental education and parental BMI on birthweight and BMI at the age of 1, 2 and 5 7 y. There was a positive gradient between parental education and birthweight (Fig. 1a). This gradient was enhanced by parental overweight. At 1 and 2 y there was no effect of either SES or parental overweight on children s BMI (Fig. 1b and 1c). At the age of 5 7 y, there was an inverse parental education gradient in BMI that was further enhanced by parental overweight (Fig. 1d). Thus, children of two overweight parents with low education had the highest mean BMI. Longitudinal relationships between birthweight and BMI at the age of 5 7 y showed that children in low and high parental education groups have different weight changes. In Table 5, SDS-BMI scores are used to illustrate changes over time. Overall, SDS-BMI decreased but there was no significant decrease for (i) children in groups with low parental education, (ii) those with two overweight parents and (iii) nonbreastfed children. Of children with high birthweight and low as well as middle parental education, 33% tended to remain within a high quartile at the age of 5 7 y. When compared with high parental education, about twice as many children of TABLE 3 Characteristics of 1,326 study children (age 5 7 y) and their parents stratified according to parental nutritional status1 Parental nutritional status No overweight2 parent (n 644) One overweight parent (n 492) Two overweight parents (n 190) Children Age, y 6.3 ( )b 6.3 ( ) 6.2 ( ) Birthweight,a g 3,440 (3,100 3,720) 3,500 (3,180 3,765)b 3,550 (3,105 3,925)b BMI, kg/m2 1 y 17.0 ( ) 17.1 ( ) 17.0 ( ) 2 y 16.3 ( ) 16.3 ( ) 16.2 ( ) 5 7 ya 15.3 ( ) 15.5 ( )b 16.4 ( )bc Prevalence, % High birthweight2d Overweight3 at 1 y Overweight3 at 2 y Overweight3 at 5 7 yd Breastfeeding 0 mo mo mo Parents Age, y Father 37.0 ( )b 38.0 ( ) 36.0 ( ) Mother 34.0 ( ) 34.0 ( ) 34.0 ( ) BMI of mother before pregnancy,a kg/m ( ) 21.9 ( )b 25.6 ( )bc Prevalence of overweight before pregnancy,d % Change,4 in BMI of mother,a % 1.8 ( ) 4.2 ( )b 9.7 ( )b Parental education level,d % Low Middle High Values are median (IQR). a Different between groups, Kruskal-Wallis test, P b Different from group with no parent overweight, Bonferroni post hoc test, P c Different from group with one parent overweight, Bonferroni post hoc test, P d Different between groups, 2 test, P BMI, body mass index; IQR, interquartile range. 2 BMI 25.0 kg/m2. 3 Birthweight 4,000 g. 4 Equal to or greater than sex- and age-specific 90th percentile of BMI according to Kromeyer-Hauschild et al. (11). 5 BMI before pregnancy minus current BMI.

5 SOCIOECONOMIC GRADIENTS IN OVERWEIGHT 793 TABLE 4 Characteristics of 1,326 study children (age 5 7 y) and their parents stratified according to breastfeeding1 Duration of breastfeeding 0mo(n 208) 6 mo(n 605) 6 mo(n 513) Children Age, y 6.2 ( ) 6.3 ( ) 6.3 ( ) Birthweight, g 3,390 (2,985 3,718) 3,470 (3,148 3,782) 3,450 (3,188 3,730) BMI, kg/m2 1ya 17.3 ( ) 16.9 ( ) 17.1 ( ) 2 y 16.4 ( ) 16.2 ( ) 16.3 ( ) 5 7 y 15.7 ( ) 15.6 ( ) 15.6 ( ) Prevalence, % High birthweight Overweight3 at1yb Overweight at 2 y Overweight at 5 7 yb Parents Age, y Fathera 36.0 ( )c 36.0 ( )c 38.0 ( ) Mothera 33.0 ( )cd 34.0 ( )c 35.0 ( ) Current BMI, kg/m2 Father 24.9 ( ) 24.7 ( ) 24.7 ( ) Mothera 23.1 ( )cd 22.7 ( )c 22.0 ( ) Prevalence of overweight,4 % Father Motherb BMI of mother before pregnancy,a kg/m ( )cd 21.6 ( ) 21.4 ( ) Prevalence of overweight before pregnancy,b % Change5 in BMI of mother, % 5.1 ( ) 3.7 ( ) 2.9 ( ) Parental education level,b % Low Middle High Values are median (IQR). a Different between groups, Kruskal-Wallis test, P b Different between groups, 2 test, P c Different from group that was breastfed 6 mo, Bonferroni post hoc test, P d Different from group that was breastfed 6 mo, Bonferroni post hoc test, P BMI, body mass index; IQR, interquartile range. 2 Birthweight 4,000 g. 3 Equal to or greater than sex- and age-specific 90th percentile of BMI according to Kromeyer-Hauschild et al. (11). 4 BMI 25.0 kg/m2. 5 BMI before pregnancy minus current BMI. low SES families and normal birthweight increased their BMI disproportionately within the observation period. Determinants of BMI at 5 7 y of age. Using the BMI of 5- to 7-y-old children as a dependent variable in a multivariate regression analysis, a total of 11.3% of the variance could be explained by BMI mother (standard regression coefficient, 0.232), BMI father (0.111), birthweight (0.135) and parental education (0.065), whereas breastfeeding was not significant. We also tried to explore the possible three-way interaction among birthweight, nutritional status and education of parents predicting BMI of 5- to 7-y-old children. Main effects were seen for birthweight (P ), parental BMI (P ) and education (P 0.05). By contrast, there were no significant interactions for birthweight parental BMI, birthweight parental education, parental education parental BMI and parental education parental BMI birthweight. DISCUSSION There are considerable and increasing data on SES gradients in health (14). As Michael Marmot stated, Within societies, health and ill-health follow a social gradient: lower socio-economic position, worse health (15). Most of the SES gradients in health status have their onset in adulthood. However, some authors have proposed that differences in BMI by social class are formed at least in part during early childhood (4). The major finding of this study was that SES gradients in nutritional status become manifest early in life. There was an inverse SES gradient in the BMI of 5- to 7-y-old children (Fig. 1, Table 2). This gradient was enhanced by parental overweight (Fig. 1). There also were inverse SES gradients in parental overweight (Table 2). By contrast, there was a positive SES gradient in birthweight (Table 2, Fig. 1). This gradient was also enhanced by parental overweight (Fig. 1). In addition, there were no associations between BMI of 1- and 2-y-old children and SES (Fig. 1). It was shown that (i) the association between SES and children s nutritional status changes during the first 6 y of life and (ii) the inverse SES gradient in overweight becomes manifest between the second and the sixth years of life. Our findings cannot provide an explanation for the association between SES and body weight in children. SES may influence health status (social causation), but health status may also contribute to SES (social drift or selection) (14). It is tempting to speculate that early manifestations of health risks and diseases are likely to contribute to social drift and thus will have a long-term effect on these children. In children SES differences in overweight may contribute to subsequent SES gradients in health status in adulthood. However, SES by itself

6 794 LANGNÄSE ET AL. also influences health status. Data from longitudinal studies show that early child development and SES are empirically linked to adult health status (16). In regard to overweight and obesity, there was a significant association between BMI in childhood or adolescence and BMI in adulthood (17 19,20). Persistence of obesity into adulthood appeared to rise linearly throughout childhood. In addition, childhood overweight has been shown to be predictive for adult morbidity and mortality (21). Antecedents of adult disease (hypertension, hyperlipidemia, impaired glucose tolerance) occur with increased frequencies in obese children and adolescents (22 26). There are only a few long-term follow-up data spanning the period from childhood to adulthood. These data suggest life-long persistence and health consequences of overweight and obesity in many children (21). Because SES contributes to childhood overweight, it also contributes to its short- and long-term health consequences. It is reasonable but presently unknown whether intraindividual SES differences in overweight persist throughout life. SES differences in adult health status have been in part explained by early education. Our present finding of SES gradients in early-onset overweight suggested that the development of unhealthy habits occurs before the age of 6 y. In fact, there are SES gradients in food intake, physical activity and inactivity in 5- to 7-y-old children (3,10,27). SES also affects early feeding practices. The prevalence of breastfeeding increased with parental education (Table 4). Our data supported previous results showing a protective effect of breastfeeding on childhood overweight, i.e., breastfed infants are less likely to be overweight in childhood (28 30). Our data also showed that compared with breastfed infants, the prevalence of overweight at the ages of 1 and 5 7 y was significantly increased in children who were not breastfed as infants (Table 4). However, using a multivariate regression analysis with children s BMI at 5 7 y as a dependent variable, breastfeeding did not reach significance. In the group of nonbreastfed infants, the mothers current and prepregnancy BMI were increased, suggesting a possible interaction between different factors. Using analysis of variance, we found no interactions among SES, parental weight and birthweight (see Results). Pragmatically, all of these data suggested that measures of obesity prevention should start very early in life and should specifically tackle overweight children from a low socioeconomic class. Parent-prepubertal offspring associations for BMI were investigated in our study, and the risk of childhood obesity significantly increased with the BMI of the parents (Table 3, Results). Using a multivariate analysis with children s BMI at the age of 5 7 y as the dependent variable, 7.6% of its variance was explained by the BMI of mothers and fathers in a previous study on the KOPS population (31). In the present study this number could be increased to 11% by adding SES, birthweight and breastfeeding to the analysis. We have previously FIGURE 1 Median birth weight, BMI at 1 y, BMI at 2 y and BMI at 5 7 y of 1326 children stratified by parental social class and nutritional status. (a) Median birth weight, ANOVA: P social class 0.061; P parental BMI 0.01; P social class parental BMI 0.977; difference between children with no versus one overweight parent, Bonferroni post hoc test: P (b) BMI at 1 y, ANOVA: NS. (c) BMI at 2 y, ANOVA: NS. (d) BMI at 5 7 y, ANOVA: P social class 0.01; P parental BMI ; P social class parental BMI 0.121; differences between children from low versus high SES and among all groups of parental nutritional status, Bonferroni post hoc test: P BW, birthweight; 0P, no parent overweight; 1P, one parent overweight; 2P, two parents overweight; NS, not significant; SES, socio-economic status.

7 SOCIOECONOMIC GRADIENTS IN OVERWEIGHT 795 TABLE 5 Standard deviation scores for body mass index (SDS-BMI) at birth and in 1,326 study children (age 5 7 y) stratified according to parental education level, parental nutritional status and breastfeeding1 n SDS-BMI at birth SDS-BMI at 5 7 y P value, WRT All children 1, ( 0.97 to 0.89) 0.05 ( 0.61 to 0.55) 0.05 Parental education level Low ( 0.44 to 0.94) 0.05 ( 0.56 to 0.77) N.S. Middle ( 0.38 to 0.89) 0.05 ( 0.61 to 0.57) 0.05 High ( 0.38 to 0.85) 0.00 ( 0.63 to 0.46) 0.05 Parental BMI2a No overweight parent ( 0.47 to 0.80) 0.04 ( 0.70 to 0.37) 0.05 One overweight parent ( 0.28 to 0.95)b 0.04 ( 0.64 to 0.57) 0.05 Two overweight parents ( 0.34 to 1.10) 0.35 (0.00 to 1.10) N.S. Breastfeeding, mo ( 0.38 to 0.99) 0.05 ( 0.45 to 0.76) N.S ( 0.37 to 0.92) 0.05 ( 0.64 to 0.59) ( 0.38 to 0.86) 0.05 (0.64 to 1.19) Values are median (IQR). a Different SDS-BMI at birth between groups, Kruskal-Wallis test, P b Different SDS-BMI at birth from group with no overweight parents. IQR, interquartile range; N.S., not significant; WRT, Wilcoxon signed rank test. 2 BMI 25.0 kg/m2. shown that parental BMI had its strongest effect in the group of overweight children (3). These data suggest a significant but limited familial effect on childhood BMI and the prevalence of childhood obesity. Some authors propose that shared environment exerts only a minor effect on nutritional traits, suggesting an impact of biological factors (32). However, family members show similarities in food preferences, eating habits and activity patterns. Thus in addition to genes, behavioral factors and/or gene-environment interactions are likely to add to children s BMI (33,34). This idea is also illustrated by the finding that inverse SES gradients in BMI are, but SES gradients in health habits are not, affected by parental overweight (3). Because the inverse SES gradients in children s BMI and the changes in BMI during the first years of life are both affected by parental overweight, our data may be taken as evidence for gene-environment interaction(s). Our data supported the positive association between SES and birthweight. SES gradients in nutritional state show considerable changes during the first years of life. The inverse SES gradient in overweight became manifest between years 2 and 6 of life. Parental BMI enhanced SES gradients in birthweight and BMI at 5 7 y of age. LITERATURE CITED 1. World Health Organization (2000) Obesity: Preventing and Managing the Global Epidemic. WHO Technical Report Series 894. WHO, Geneva. 2. Sobal, J. & Stunkard, A. (1989) Socio-economic status and obesity. A review of literature. Psychol. Bull. 105: Langnaese, K., Mast, M. & Mueller, M. J. (2002) Social class differences in overweight in pre-pubertal children in northwest Germany. Int. J. Obes. 26: Laitinen, J., Power, C. & Järvilen, M.-J. (2001) Family social class, maternal body mass index, childhood body mass index and age of menarche as predictors of adult obesity. Am. J. Clin. Nutr. 74: Spencer, N., Bambang, S., Logan, S. & Gill, L. (1999) Socio-economic status and birthweight: comparison of an area-based measure with Registrar General s social class. J. Epidemiol. Commun. Health 53: Pattenden, S., Dolk, H. & Vrijheid, M. (1999) Inequalities in low birthweight: parental social class, area deprivation, and lone mothers. J Epidemiol. Commun. Health. 53: Teranishi, H., Nagakawa, H. & Marmot, M. (2001) Social class difference in catch up growth in a national British cohort. Arch. Dis. Child. 84: Pietiläinen, K. H., Kaprio, J., Räsänen, M., Winter, T., Rissanen, A. & Rose, R. J. (2001) Tracking of body size from birth to late adolescence: contributions of birth length, birthweight, duration of gestation, parent s body size and twinship. Am. J. Epidemiol. 154: Müller, M. J., Asbeck, I., Mast, M., Langnäse, K. & Grund, A. (2001) Prevention of obesity-more than an intention. Concept and first results of the Kiel Obesity Prevention Study (KOPS). Int. J. Obes. 25 (Suppl. 1): S66 S Müller, M. J., Mast, M., Asbeck, I., Langnäse, K. & Grund, A. (2001) Prevention of obesity: is it possible? Obes. Rev. 2: Langnäse, K. (2001) Einflu sozialer Faktoren auf die Manifestation und Prävention der Adipositas bei Kindern. Ph.D. thesis. Schriftenreihe des Instituts für Humanernährung und Lebensmittelkunde der Christian-Albrechts- Universität Kiel. 12. Kromeyer-Hauschild, K., Wabitsch, M., Kunze, D., Geller, F., Gei, H.C., Hesse, V., von Hippel, A., Jaeger, U., Johnsen, D., Korte, W., Menner, K., Müller, G., Müller, M. J., Niemann-Pilatus, A., Remer, T., Schaefer, F., Wittchen, H.-U., Zabransky, S., Zellner, K., Ziegler, A. & Hebebrand, J. (2001) Perzentile für den Body Mass Index für das Kindes- und Jugendalter unter Heranziehung verschiedener deutscher Stichproben. Percentiles of body mass index in children and adolescents evaluated from different regional German studies. Monatsschrift Kinderheilkunde 149: Cole, F. J. (1990) The LMS method for constructing normalized growth standards. Eur. J. Clin. Nutr. 44: Evans, T., Whitehead, M., Didrichsen, F., Bhuiya, M. & Wirth, A., eds. (2001) Challenging Inequities in Health. From Ethics to Action. Oxford University Press, Oxford. 15. Marmot, M. (1999) Epidemiology of socio-economic status and health: are determinants within countries the same as between countries? In: Socio-economic status and health in industrial nations. Social, psychological and biological pathways (Adler, N. E., Marmot, M., McEwen, B. S. & Stewart, J., eds.). Ann. N. Y. Acad. Sci. 896: Hertzman, C. (1999) The biological embedding of early experience and ist effect on health in adulthood. Ann. N. Y. Acad. Sci. 896: Guo, S. S., Roche, A. F., Cameron Chumlea, W., Gardner, J. D. & Siervogel, R. M. (1994) The predictive value of childhood body mass index for overweight at age 35y. Am. J. Clin. Nutr. 59: Must, A., Jacques, P. F., Dallal, G. E., Bajema, C. J. & Dietz, W. H. (1992) Long-term morbidity and mortality of overweight adolescents. N. Engl. J. Med. 327: Whitaker, R. C., Wright, J. A., Pepe, M. S., Seidel, K. D. & Dietz, W. H. (1997) Predicting obesity in young adulthood from childhood and parenteral obesity. N. Engl. J. Med. 337: Parsons, T. J., Power, C., Logan, S. & Summerbell, C. D. (1999) Childhood predictors of adult obesity: a systematic review. Int. J. Obes. 23 (Suppl. 8): Dietz, W. H. (1998) Health consequences of obesity in youth: childhood predictors of adult disease. Pediatrics 101: Power, C., Lake, I. U. & Cole, T. J. (1997) Measurement and long-term health risks of child and adolescent fatness. Int. J. Obes. 21: Berenson, G. S., Srinivasan S. R., Bao, L. N., Newman, W. P., Tracy, R. E. & Wattigney, W. A., for the Bogalusa Heart Study. (1998) Association between multiple cardiovascular risk factors and atherosclerosis in children and young adults. N. Engl. J. Med. 338: Berenson, G. S., Wattigney, W. A., Bao, W., Srinivasan, S. R. & Radhakrishuamurrthy, B. (1995) Rationale to study the early natural history of heart disease: the Bogalusa Heart Study. Am. J. Med. Sci. 310 (Suppl 1): Mahoney, L. T., Burns, T. L., Stanford, W., Thompson, B. H., Witt, I. D., Rost, C. A. & Lauer, R. M. (1996) Coronary risk factors measured in childhood and young adults life are associated with coronary artery calcification in young adults: the Muscatine Study. J. Am. Coll. Cardiol. 27:

8 796 LANGNÄSE ET AL. 26. Vanhala, M., Vanhala, P., Kumpusalo, E., Halonon, P. & Tallala, I. (1998) Relation between obesity from childhood to adulthood and the metabolic syndrome: population-based study. Br. Med. J. 317: Müller, M. J., Mast, M., Körtzinger, I., Grund, A. & Langnäse, K. (1999) Physical activity and diet in 5 to 7 years old children. Public Health Nutr. 3 (A): Kramer, M. S. (1981) Do breast-feeding and delayed introduction of solid foods protect against subsequent obesity? J. Pediatr. 98: Von Kries, R., Koletzko, B., Sauerwald, T., von Mutius E., Barnert, D., Grunert, V. & von Hoss, H. (1999) Breast feeding and obesity: cross-sectional study. Br. Med. J. 319: Frongillo, E. A. (2001) Growth of the breast-fed child. In: Nutrition and Growth (Martorell, R. & Haschke, F., eds.), 47th Nestle Nutrition Workshop, Lippincott Williams & Wilkins, Philadelphia. 31. Danielzik, S., Langnäse, K., Mast, M., Spethmann, C. & Müller, M. J. (2002) Impact of parental BMI on the manifestation of overweight 5 7 year old children. Eur. J. Nutr. 41: Vogler G. P., Sörensen, T. I. A., Stunkard, A. J., Srinivasan, M. R. & Rao, D. C. (1995) Influences of genes and shared family environment on adult body mass index assessed in an adoption study by a comprehensive path model. Int. J. Obes. 19: Birch, L. L. & Krahnstoever-Davison, K. (2001) Family environmental factors influencing the developing behavioural controls of food intake and childhood overweight. Pediatr. Clin. North Am. 48: Krahnstoever Davison, K. & Birch, L. L. (2002) Obesigenic families: parent s physical activity and dietary intake patterns predict girl s risk of overweight. Intl. J. Obes. 26: