The vulnerable child in an obesogenic environment : Associations between sociodemographic and behavioural factors and weight-related anthropometric variables in Norwegian children
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Background: Childhood overweight and obesity represent important challenges. As treatment is difficult, the attention given to prevention is warranted. To identify children at risk of overweight and obesity, knowledge about the behavioural determinants is needed, but also knowledge about the psychosocial and environmental factors driving the obesity epidemic.
Aim: The overall aim of this thesis is to identify children at risk of overweight or obesity by exploring the familial, sociodemographic, and behavioural factors associated with weight status and one-year weight gain in a population of healthy Norwegian children aged 4 to 16 years.
Materials and methods: This study was based on anthropometric measurements, and sociodemographic and behavioural data collected through parental questionnaires in the Bergen Growth study (BGS). In the first paper of the study, sociodemographic and behavioural determinants and their association to overweight and obesity were examined in a cross-sectional study of 2281 children aged 6-15 years. In the second paper, sociodemographic and behavioural determinants and their association to five different anthropometric measures, Body mass index (BMI), waist circumference (WC), waist-to-height ratio (WHtR), subscapular skinfold (SSF), and triceps skinfold (TSF), were analysed in 3063 children aged 4-15. In the third paper, the association between sociodemographic and family determinants and their association to BMI z-score and BMI z-score increments after one year were studied in 769 children aged 6-15 with anthropometric data collected at baseline and also after one year.
Results: In the first paper, the prevalence of overweight and obesity was higher in children of parents with a lower education (18% vs. 12%, p<0.001), and they had a more obesogenic lifestyle. Children with obesity reported eating sweets less frequently than the other children. More hours of screen time was associated with overweight (OR 1.25, 1.07; 1.47) and the presence of a TV set in the child’s bedroom was associated with obesity (OR 1.81, 1.04; 3.17). A low intake of fruit and vegetables, more than 2 hours of screen-time a day, and less than 4 hours a week spent in physical activity were common risk factors in all children, independent of weight status. In the second paper, physical activity was found to be unrelated to BMI, but associated with all the other anthropometric measures in linear regression analyses. Physical activity was associated with a lower WC (b=-0.02), WHtR (b=-0.03), SSF (b=-0.04) and TSF (b=-0.06) in girls, and a lower SSF (b=-0.07) and TSF (b=-0.07) in boys. A higher intake of vegetables was associated with a higher WC and TSF in girls. The presence of a TV set in the bedroom was associated with a higher SSF and BMI in boys before adjusting for the BMI z-score. In the third paper, the prevalence of OWOB increased from 16.6% to 17.8% over a year (p<0.001). Maternal BMI was associated with higher BMI increments in their offspring (OR 1.07, 1.01; 1.13). A blended family structure was frequent in the study population (25% of children), and was associated with a higher risk of weight gain above 1 standard deviation (SD) over a year (OR 1.82, 1.16; 2.88).
Conclusion: The prevalence of overweight and obesity was higher in children of parents with a low educational level. Obesogenic behaviours were also more frequent in these children. A high screen time and the presence of a TV set in the child’s bedroom were associated with overweight and obesity. Known risk factors for overweight and obesity were common in all children, independent of weight status. Physical activity was unrelated to the BMI, but associated to skinfold thickness in both sexes, and also to WC and WHtR in girls. When studying physical activity in children, the BMI should be complemented with other anthropometric measures. A blended family structure was common, and was associated with higher one-year BMI increments. Childhood life events can affect weight development. BMI increments could be used to monitor weight change and could be valuable in identifying children at risk of developing overweight or obesity.