Overweight and respiratory and cardiovascular health in children: the PIAMA birth cohort study

Today’s children and adolescents have a much higher prevalence of overweight than the generation of their parents had in their childhood. The prevalence of asthma symptoms has also increased at the end of the last century and associations between overweight and asthma have been convincingly shown in previous research. The increase in childhood and adolescent overweight might enhance the prevalence of cardiovascular diseases or earlier onset of cardiovascular disorders and the same can be hypothesized for lung diseases. The Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study enables the study of associations between childhood overweight on the one hand and respiratory health and early indicators of cardiovascular health in adult life on the other hand. 3963 children participate in this prospective birth cohort study with yearly questionnaires and medical examinations at ages 4, 8 and 12 years. In the Netherlands the prevalence of obesity is relatively low compared with that in the UK and USA. However, we observed higher blood pressure levels, more adverse cholesterol concentrations and more asthma symptoms in overweight than in normal weight children. Furthermore, in the 12-year-old children we observed similar blood pressure and cholesterol levels in normal weight children with and without a history of overweight. This suggests that the effects of overweight on blood pressure and cholesterol might be reversible, which is promising. In the studies with cardiovascular and respiratory outcomes, we assessed the relative importance of waist circumference and BMI in these associations. We have not demonstrated that children’s waist circumference is always more important than BMI in associations with health outcomes. However, we have several findings indicating that waist circumference is at least as strongly associated with adverse health outcomes as BMI is. Furthermore, we found the early-life determinants maternal pre-pregnancy overweight, maternal smoking during pregnancy and rapid infant weight gain to be associated with 8-year-olds’ cholesterol concentrations. BMI was associated with current asthma symptoms, but a high BMI and large waist circumference were not associated with lower lung function, measured as FEV1­ and FVC, in 8-year-old children. Over the 4-8 age range, we prospectively studied the association between BMI and asthma symptoms to assess whether this association could be explained by pro-inflammatory proteins such as hs-CRP, C3 and C4. We found a strong cross-sectional association between BMI and asthma symptoms. We did not find evidence for a role of the measured pro-inflammatory proteins in the association between BMI and asthma symptoms. Furthermore, waist circumference measured and reported by the parents corresponded well with the waist circumference measured by the professionals, indicating that reported waist circumference may be used to study associations between waist circumference and risk factors or health outcomes. The most important conclusions of this thesis were, firstly, that already in childhood being overweight has adverse consequences; overweight children had higher blood pressure levels, more adverse cholesterol concentrations and more asthma symptoms than normal weight children. Secondly, waist circumference measured and reported by parents corresponded well with waist circumference measured by professionals.