Economics and Human Biology 2 (2004) 107–118
Social inequality and obesity in Czech school children J. Vignerová a,∗ , P. Bláha b , K. Ošancová a , Z. Roth a a
Department of Biostatistics, National Institute of Public Health, Srobarova 48, 100 42 Prague, Czech Republic b Department of Anthropology and Human Genetics, Faculty of Science, Charles University, Prague, Czech Republic
Received 12 December 2003; received in revised form 12 December 2003; accepted 12 December 2003
Abstract This study uses logistic regressions to consider the effect of social factors, physical activity, meal frequency and BMI of parents on children’s body mass index (BMI) values. Three thousand three hundred and sixty-two children aged 7–11 years were examined in 38 schools in the Czech Republic. Six anthropometric characteristics were assessed in 1999–2000. Most important factors influencing children’s BMI values were: obesity of both or at least one of the parents, being an only child, residence in small communities, and irregular breakfasts. © 2004 Elsevier B.V. All rights reserved. JEL classification: I10 Keywords: Body mass index; Overweight; Obesity; Czech Republic; Children; Welfare
1. Introduction Despite an overall rise in prosperity in recent years, the “health gap” between those at the top and those at the bottom on the social scale, is not decreasing, as it was assumed at the Round Table Conference in Brussels reference (Round Table Conference, 2001). Overweight and obesity in children are one of the diseases which influence substantially the future quality of life and health of individuals. The ratio of overweight and obese people has increased in all developed countries. Thus, there is reason to be concerned. Overweight
∗
Corresponding author. Tel.: +420-26-708-2304; fax: +420-26-708-2121. E-mail address:
[email protected] (J. Vignerov´a). 1570-677X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ehb.2003.12.004
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in prepubertal children implies a high risk of overweight or obesity in adulthood (e.g. WHO Technical Report Series, 2000).1 The objective of the current study was to assess the prevalence of overweight and obesity in Czech children aged 7.00–10.99 years and to evaluate its social correlates including the influence of physical activity of the children and their meal frequency on their body weight.
2. Methods The study was carried out between September 1999 and April 2000. Thirty-eight schools were randomly selected from all 14 regions of the Czech Republic. A total of 3362 children aged 7.00–10.99 years (1694 boys and 1668 girls) were examined.2 In addition, questionnaires were completed by children and their parents in which meal frequency of the children and their physical activity were recorded. The questionnaire was completed by all children examined. The return rate of the questionnaire addressed to the parents was 82.7%. The parents reported their education, height, body weight, and number of children in the family. Six anthropometric characteristics of the children were recorded: height, body weight, arm circumference, circumference of the abdomen and hips, and mid-thigh circumference. The assessment was made according to Martin and Saller’s method (1957). The body mass index (BMI) and waist/hip ratio (WHR) were calculated. As cut off points for assessment of overweight and obesity the values of the 90th and 97th percentile of BMI reference values for the Czech child population of 1991 were used (Table 1) (Lhotská et al., 1993). The parents were divided into two groups (underweight and normal: BMI < 25; overweight and obese: BMI ≥ 25 (WHO Technical Report Series, 2000). By combination of these two categories of fathers and mothers three groups of parents were created: 1, no parent overweight; 2, one parent overweight; 3, both parents overweight. If the required characteristics were reported for only one parent the child was discarded from further analysis. The parents were divided into four categories by the size of their place of residence (Table 1). In addition, two educational groups were created: lower level (elementary education and manual workers), and higher level (secondary and university education), and thereafter the children were divided into three groups: 1, both parents lower educational level; 2, one parent lower educational level; 3, both parents higher educational level. If the necessary characteristics were reported only for one parent, the child was dismissed from further analysis. No significant difference was found in the prevalence of overweight and obesity between the categories of two and three or more children in the family and, therefore, only two categories were used in the analysis: 1, one child in family; 2, two and more children in family. 1 The European Childhood Obesity Group (ECOG) tried to organize a joint project to assess the prevalence of obesity in school children of 14 European countries (Lehingue, 1999). The joint project was not implemented so far. 2 The anthropometric measurements were made by three students of Anthropology, Faculty of Sciences, Charles University, Prague.
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Table 1 Distribution of children by community size Number of inhabitants
%
Number of children
Prague (>1 million) <1 million <10,000 <5,000
10.4 25.5 29.8 34.4
347 854 992 1,152
The children were asked about the number of sports they pursued. For purposes of analysis, four categories were formed: 1, no sports; 2, one to three sports, 3, four to six sports; 4, more than six sports. The next question pertained to the frequency of TV watching: 1, afternoon and evening programs daily; 2, afternoon or evening programs daily; 3, frequent watching of children’s program; 4, occasional TV watching. The third question concerned the frequency of PC games: 1, every day; 2, occasionally; 3, never. The children were also asked whether they ate breakfast (yes, no, occasionally), whether they have a mid-morning snack at school (yes, no), whether they have lunch in the school canteen (yes, no) and whether they have an afternoon snack (yes, no, occasionally). For statistical analysis the answers “no” and “occasionally” related to breakfast and afternoon snack were combined as “no”. 2.1. Statistical analysis Chi-square tests, using EpiInfo software, were made separately for every investigated factor. In addition, logistic regression was done using SPSS, version 7.0. In the first step, of the logistic regression all variables were included in the analysis. In the second step, the “Forward Stepwise” method was used which included in the analysis only variables which had a significant influence on the dependent variable. The dependent variable was 0 if the BMI of the child was below the 90th percentile of the Czech reference population, and 1 otherwise. Independent variables: sex (1, 2), BMI of parents (1, 2, 3), education of parents (1, 2, 3), number of children in family (1, 2), size of community where child lives (1, 2, 3, 4), sports activities (1, 2, 3, 4), watching TV (1, 2, 3, 4), PC games (1, 2, 3), breakfast (1, 2), mid-morning snack (1, 2), school lunch (1, 2), afternoon snack (1, 2).
3. Results 3.1. Bodily characteristics and nutritional status Among 7- and 8-year-old children of both sexes a statistically significant higher mean height was recorded as compared with reference values of the Fifth Nationwide Anthropological Survey (CAV) in 1991 (Table 2). However, among the 9- and 10-year-olds, the mean height does not differ from the reference values. This pattern is consistent with slowing down of the secular trend of height in older age groups of children. Although body weight is also
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Table 2 Anthropometric characteristics Age group
Boys
Girls
Reference 1991
n
7.50 8.50 9.50 10.50
289 542 574 283
7.62 8.54 9.50 10.40
0.27 0.29 0.28 0.26
7.50 8.50 9.50 10.50
313 528 545 271
7.62 8.52 9.49 10.36
0.26 0.29 0.29 0.26
Body height (cm) 7.00–8.00 7.50 8.00–8.99 8.50 9.00–9.99 9.50 10.00–10.99 10.50
289 542 574 283
128.84∗∗ 133.96∗∗ 138.78 143.23
5.58 5.84 6.19 6.53
126.90 132.60 138.15 143.80
313 528 545 271
128.35∗∗ 133.33∗∗ 138.27 143.29
5.73 6.20 6.52 6.88
Body weight (cm) 7.00–8.00 25.98 8.00–8.99 28.97 9.00–9.99 32.41 10.00–10.99 36.08
289 542 574 283
26.93∗∗ 30.06∗∗ 32.62 36.33
4.85 6.47 6.37 7.74
25.77 28.68 32.11 35.64
313 528 545 271
26.58∗∗ 29.24∗ 32.54 36.00
5.11 5.66 6.60 8.46
Arm circumference (cm) 7.00–8.00 18.76 8.00–8.99 19.48 9.00–9.99 20.33 10.00–10.99 21.12
276 509 537 267
18.85 19.45 20.10∗ 20.87
2.03 2.36 2.30 2.62
18.75 19.53 20.51 21.13
300 495 510 250
18.84 19.46 20.22∗ 20.89
2.07 2.22 2.31 2.70
Abdomen circumference (cm) 7.00–8.00 57.26 8.00–8.99 59.05 9.00–9.99 61.29 10.00–10.99 63.25
277 509 537 267
59.17∗∗ 62.17∗∗ 63.63∗∗ 66.46∗∗
6.06 7.23 6.81 7.81
56.18 57.88 60.02 61.33
300 495 510 250
59.32∗∗ 61.73∗∗ 64.09∗∗ 66.15∗∗
6.49 6.97 7.30 8.88
Hip circumference (cm) 7.00–8.00 65.73 8.00–8.99 68.35 9.00–9.99 71.38 10.00–10.99 74.05
277 509 537 267
66.05 69.02∗ 71.22 74.26
5.43 6.28 6.10 7.09
66.58 69.27 72.48 75.21
300 495 510 250
67.20 69.72 72.67 75.37
6.05 6.20 6.44 7.59
Mid-thigh circumference (cm) 7.00–8.00 34.4 8.00–8.99 36.7 9.00–9.99 38.1 10.00–10.99 39.5
277 509 537 267
36.07∗∗ 38.28∗∗ 39.82∗∗ 41.87∗∗
3.88 4.71 4.49 5.54
35.5 37.1 38.9 40.9
300 495 510 250
37.46∗∗ 39.37∗∗ 41.34∗∗ 43.07∗∗
4.33 4.68 4.83 5.36
Body mass index (kg/m2 ) 7.00–8.00 15.93 8.00–8.99 16.32 9.00–9.99 16.84 10.00–10.99 17.43
289 542 574 283
16.15 16.64 16.84 17.57
2.22 2.70 2.46 2.77
15.93 16.24 16.73 17.13
313 528 545 271
16.04 16.37 16.92 17.40
2.29 2.44 2.64 3.03
Waist/hip ratio 7.00–8.00 8.00–8.99 9.00–9.99 10.00–10.99
277 509 537 267
89.52∗∗ 89.96∗∗ 89.26∗∗ 89.39∗∗
3.78 3.97 3.71 3.77
84.47 83.62 82.83 81.57
300 495 510 250
88.21∗∗ 88.45∗∗ 88.09∗∗ 87.63∗∗
4.05 4.31 4.26 5.17
Age (years) 7.00–8.00 8.00–8.99 9.00–9.99 10.00–10.99
∗
87.18 86.51 85.85 85.39
Mean
Statistical significance at P < 0.05 level. Statistical significance at P < 0.01 level.
∗∗
S.D.
Reference 1991
n
Mean
S.D.
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Table 3 Ratio of overweight and obese children—% (χ2 -test)
Boys Girls Boys and girls
n
Obese (>97th percentile)
Overweight (90th–97th percentile)
Normal (<90th percentile)
1,694 1,668 3,362
6.0** 5.6** 5.8**
7.1 6.3 6.8
86.9 88.1 87.4
Significantly different from expected frequency of 7% (BMI > 90th percentile, Reference 1991), or 3% (BMI > 97th percentile, Reference 1991) at **P < 0.01 level.
greater among the 7- and 8-year-old children, commensurate with their greater height, the mean BMI values, however, are not significantly higher in any of the age groups in either sex. Furthermore, significantly higher values were recorded for the abdominal circumference and mid-thigh circumference in all age groups and in both sexes. With the increased abdominal circumference a significant increase of the waist/hip ratio is found. An increase of these values indicates a change of the adipose tissue distribution, which may be associated with the children’s physical activity. Table 3 presents the frequency of children exceeding the 90th and 97th percentile of the 1991 Czech reference population. The ratio of overweight (BMI 90th–97th percentile) children is close to the expected 7.0%. However, the ratio of obese (BMI > 97th percentile) children almost doubled: it increased from 3.0% in 1991 to 5.8% in 2000. The mean BMI value of mothers is 23.1 (S.D. 3.5), of fathers 26.1 (S.D. 3.2). The ratio of overweight and obese children in the sample increases with increasing BMI values of parents, and is statistically significant (χ2 -test, P < 0.0001) (Table 4). With an increasing level of education the proportion of parents with lower BMI values, the ratio of families Table 4 Ratio of parents in categories by educational level—% (χ2 -test) n
Educational level of parents Both low
One low
Both high
Total (%)
P
933 1,277 423
27.0 32.3 40.2
26.5 27.6 31.0
46.5 40.1 28.8
100.0 100.0 100.0
0.000
Number of children in the family One 427 Two or more 2,141
25.5 32.6
30.7 27.2
43.8 40.3
100.0 100.0
0.016
Settlement size Prague >10,000 >5,000 <5,000
19.8 31.2 28.5 39.1
23.1 23.8 31.6 28.6
57.1 45.0 40.0 32.3
100.0 100.0 100.0 100.0
0.000
BMI of parents Neither overweighta One overweighta Both overweighta
a
Or obese.
308 622 811 892
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Table 5 Ratio of obese and overweight children by parental BMI and social categories—% (χ2 -test) n
Obese (>97th percentile)
Overweight (90th–97th percentile)
Normal (<90th percentile)
Total (%)
P
1,084 1,329 430
2.7 5.0 14.0
4.4 6.8 10.0
92.9 88.2 76.0
100.0 100.0 100.0
0.000
Educational level of parents Both low 829 One low 729 Both high 1,062
7.0 6.0 3.3
5.4 7.1 6.8
87.6 86.8 89.9
100.0 100.0 100.0
0.003
Number of children in the family One 500 Two or more 2,263
7.8 4.9
9.0 5.7
83.2 89.5
100.0 100.0
0.000
Number of inhabitants Prague >10,000 >5,000 <5,000
2.3 5.5 6.0 6.9
5.2 5.9 6.8 7.8
92.5 88.6 87.2 85.2
100.0 100.0 100.0 100.0
0.013
BMI of parents Neither overweighta One overweighta Both overweighta
a
347 854 992 1,152
Or obese.
with an only child, and the proportion living in larger communities all increase (Table 5) (Vignerová et al., 1998). 3.2. Social aspects The ratio of obese children declines with increasing educational level of both parents (Table 4). Among children whose both parents have a lower educational level the rate is almost double compared to those whose both parents have a higher educational level (7.0 and 3.3%, respectively). The ratio of children with BMI values above the 90th percentile is 12.4, 13.1, and 10.1% in the different groups of parents. The ratio of obese and overweight children is markedly higher in the group of children who do not have a sibling. In this group of children 7.8% are obese and 9.0% overweight, while in the group with more than one child per family the corresponding figures are 4.9 and 5.7%, respectively. The ratio of obese and overweight children declines with increasing size of the residence community. In communities with less than 5000 inhabitants there were three times as many obese children as in Prague. 3.3. Lifestyle A statistically significant difference (χ2 ) in the rate of obesity was found with respect to physical activity. The higher the number of sports in which the children participated, the lower are the BMI values (P = 0.001). In contrast, TV watching has no association with obesity (P = 0.35) while playing PC games does to some extent (P = 0.077) (Fig. 1). There is also a significant difference between the two groups of children as regards regular
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Fig. 1. Physical activity of children. Sport activity: 1, no sports; 2, one to three sports; 3, four to six sports; 4, more than six sports. TV watching: 1, afternoon and evening programs daily; 2, afternoon or evening programs daily; 3, frequent watching programs for children; 4, occasional TV watching. PC games: 1, every day; 2, occasionally; 3, never.
consumption of breakfasts and afternoon snacks. The results of the χ2 -test are as follows: breakfast P < 0.000, mid-morning snack P = 0.399, school lunch P = 0.906, and afternoon snack P < 0.040 (Fig. 2). 3.4. Logistic regressions The logistic regression confirms that there was no substantial difference in the prevalence of obesity between genders even if the effect of some of the independent variables differ to
Fig. 2. Meal frequency of children.
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Table 6 Logistic regression: dependent variable: BMI values above the 90th percentile of Czech (1991) reference values Variable
Both sexes Coefficient
Sex (boys) BMI of parents (neither overweight) Both overweight One overweight Educational level of parents (both high educational level) Both parents low One parent low Number of children in the family (two and more) One child Number of inhabitants (>1 million inhabitants) <5,000 inhabitants 5,000–10,000 inhabitants 10,000 to 1 million inhabitants Sports activity (<6 kinds of sports) No sports 1–3 kinds of sports 4–6 kinds of sports PC games (never) Occasionally Every day TV watching (occasionally) Frequent watching of children programs Daily watching of afternoon or evening programs Daily watching of afternoon and evening programs Breakfast (yes) No breakfast Mid-morning snack (yes) No mid-morning snack School lunch (yes) No school lunch Afternoon snack (yes) No afternoon snack Number of children
0.058 0.671 1.516
Boys P 0.659 0.000∗∗ 0.000∗∗ 0.000∗∗ 0.494
Coefficient
0.591 1.447
Girls P 0.000∗∗ 0.012∗ 0.000∗∗ 0.742
Coefficient
0.787 1.615
P 0.000∗∗ 0.001∗∗ 0.000∗∗ 0.631
−0.164 0.013
0.318 0.936 0.000∗∗
−0.161 −0.007
0.489 0.975 0.000∗∗
−0.139 0.089
0.559 0.706 0.030∗
0.724
0.000∗∗ 0.006∗∗
0.917
0.000∗∗ 0.230
0.514
0.030∗ 0.016∗
0.699 0.573 0.197
0.467 0.197 −0.011
0.360
0.184 0.578 0.976 0.709 0.779 0.353 0.395 0.546 0.571 0.271 0.070 0.193
1.037 0.937 0.454
0.152
0.006∗∗ 0.026∗ 0.472 0.109 0.738 0.023∗ 0.088 0.604 0.574 0.318 0.634 0.450
−0.108
0.008∗∗ 0.016∗ 0.277 0.094 0.361 0.021∗ 0.090 0.796 0.500 0.828 0.819 0.726
0.013
0.945
0.177
0.516
−0.106
0.704
−0.092
0.601
−0.282
0.290
0.110
0.644
0.138 0.558 0.407 −0.127 −0.150
−0.191 0.287 0.251 −0.166 −0.252
0.011∗ 0.334 0.712
0.298 0.198
0.332 −0.760
0.631 0.073
−0.270 −0.044
0.009∗∗ 0.492
0.160
0.533 0.998 0.718
0.126 0.849
0.205
0.120
0.809 −0.053
0.274 0.642
0.206
−0.087
0.492
2,477
1,249
1,228
0.011∗
Calculations referred to category where lowest prevalence of overweight and obesity in children is expected, i.e. always to category of the variable in parentheses. ∗ Statistical significance at P < 0.05 levels. ∗∗ Statistical significance at P < 0.01 level.
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Table 7 Odds ratio and confidence interval of statistically significant risk factors (logistic regression—Forward Stepwise method)
Both parents overweight One parent overweight One child in the family <5,000 inhabitants 5,000–10,000 inhabitants 10,000 to 1 million inhabitants Breakfast “no” or occasionally
OR
95% CI for OR Lower
Upper
4.5928 1.9473 2.0764 2.1039 1.8918 1.3392 1.4413
3.1891 1.4004 1.5253 1.2865 1.1484 0.7893 1.1172
6.6142 2.7079 2.8266 3.4407 3.1164 2.2724 1.8594
some degree (Table 6).3 The BMI of the parents has a significant influence on the obesity rate of their children, even if only one parent is overweight. There is a higher risk of overweight and obesity among children from families with only one child. A significant association was also found between the prevalence of overweight and obesity and the size of the community where the child lives. However, no difference was found between Prague and large towns with a population of 10 000 to 1 million. However, the effect of this variable is only significant among the girls. This might be an indication that in larger towns there could be more of a peer pressure for girls to conform to feminine ideals than in village communities. There is no influence of the educational level of the parents on the obesity rate of their children in this model, perhaps because of the high negative correlation between educational attainment and obesity among the parents. Irregular breakfast or skipping breakfast increases significantly the risk of development of overweight and obesity, particularly among boys, and skipping afternoon snacks among the girls. Table 7 presents the values of the odds ratios (OR) and their confidence interval (CI) of those factors which were included by the Forward Stepwise method in the logistic regression as being significant. Overweight of both parents increases the risk of overweight in children more than fourfold. A more than twofold risk is experienced by only children and by children from small communities with a population under 5000 inhabitants. An almost twofold risk was recorded in children from small communities (with a population under 10 000). Overweight of one parent increases the risk 1.7 times and the risk is 1.4 times higher in children from towns with a population under 1 million and children who do not eat breakfast regularly.
4. Discussion The basic body parameters of the Czech child population have been comparable to those prevalent in developed countries (Vignerová and Bláha, 1998). The rising trend of 3 Some subjects were excluded from this part of the analysis because of incomplete data. The coefficients indicate the changes of individual categories of a given characteristic compared with the category to which the changes are related, i.e. the category where the lowest prevalence of overweight and obesity was recorded.
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overweight and obese children in advanced countries is also consistent with the results reported here (Jebb and Lambert, 2000; Livingstone, 2000; Kromeyer-Hautschild et al., 1999; Reilly et al., 1999). There is a large increase in the proportion of Czech children whose BMI value is higher than the 97th percentile of 1991 reference values. Twenty percent of 195 obese children in our study have their BMI values above the 99th percentile of the 1991 reference values. The close relationship between adiposity of parents and their offspring reflects both genetic and cumulative environmental factors including behavioral ones (Parsons et al., 1999; Komlos et al., 2004). In the present sample parental obesity is the most significant risk factor: 62.0% of the overweight or obese children have at least one parent overweight or obese. Although obesity is also associated with genetic factors (Maffeis, 2000; Parsons et al., 1999; ILSI Europe Overweight and Obesity in Children Task Force, 2000), the trend of the increasing obesity is due, above all, to the changing nutritional and physical activity pattern of the population (WHO Technical Report Series, 2000). Mainly social, environmental and psychological reasons can explain such changes in the lifestyle of parents, and thus also children. Higher education of the parents has a positive effect on the general lifestyle of the children—their physical activity, leisure time activities, dietary habits (Maffeis, 2000; Koziel et al., 2000). According to the Fifth Nationwide Anthropological Survey of Children and Adolescents in the Czech Republic in 1991 an association between the parents’ education and the bodily development of the child was confirmed (Vignerová et al., 1998). A similar pattern is evident in this sample as well, insofar as children of parents with a lower educational level are twice as likely to be obese (7.0%) as children of parents with a higher educational level (3.3%) (Table 4). However, this was not the case among overweight children—as the lower educational level had a lower level of overweight (5.4%) than those of higher education levels (6.8 and 7.1%). This pattern might be the reason why the educational level of the parents was insignificant in the logistic regression. An analysis of the association between mother’s education and the children’s life style showed that the life style of children with mothers of higher education was for the number of sports pursued, watching TV, and meal frequency significantly more favorable for the avoidance of obesity in comparison with the other children (Vignerová and Bláha, 2001). Only playing PC games was unfavorable for this group. Hence, not only education but also purposeful cultural activities may have positive results on the prevention of obesity. The high risk of being overweight or obese among only children cannot be explained by the lower educational levels of the parents and probably neither by heredity nor the lifestyle of the family.4 However, it might be the case that families with one child can afford to spend more on calorie-rich food per child than households with more than one child. Overweight and obesity of girls in smaller communities is possibly associated with different lifestyles or different acceptance (peer pressure) as compared with the urban girls. It is noteworthy, however, that the proportion of parents with a higher educational level rises significantly with the size of the community. Therefore, the association between the 4 The mean BMI values of mothers of the only children are even significantly lower (mean BMI = 22.4) than those of families with several children (mean BMI = 23.1). Similarly, the analysis of children’s life style among one child families did not provide significant differences (Vignerov´a and Bl´aha, 2001).
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increasing prevalence of obesity in smaller communities may also be brought about by the education effect. As regards lifestyle, there is the obvious problem of quantification of the actual energy intake and output. Even if the validity of the children’s replies cannot be tested, the association between having irregular meals and being overweight or obese has been mentioned by other authors (Morgan et al., 1986; Wyatt et al., 2002). The mechanism by which high socioeconomic status in developed countries provides some protection against obesity has not been elucidated so far, and there are probably multiple causes of this phenomenon (WHO/FAO Expert Consultation on diet, nutrition and the prevention of chronic diseases, 2002). The present results show that the problem is increasing also in the Czech Republic, and confirm the association of high BMI values with several social and cultural factors.
Acknowledgements This research was implemented within the framework of a grant of the Internal Grant Agency Ministry of Health, Registration Number NJ/5158-3.
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