Introduction An inflammatory link and common genetic factors have been discussed regarding the relation between BMI and asthma. We investigated the relation between obesity and asthma symptoms, and effect modification by atopy and parental allergic disease in Phase 2 of the International Study of Asthma and Allergies in Childhood.
Methods In a population-based cross-sectional study, 10 600 children aged 8–12 from 22 centres worldwide were studied with standardised parental questionnaires. Height and weight were measured and age- and sex-specific international BMI cut-off-points were used to define obese children. Atopy was assessed with skin prick testing. Adjusted ORs for each centre were combined with meta-analysis random effects models.
Results Obesity was associated with wheeze in the past year in boys (adjusted OR 1.93 (95% CI 1.46 to 2.57) and girls 1.51 (1.02 to 2.24). In boys and girls, the effect was the same among atopic and non-atopic children. In boys, the OR was increased in children with reported parental allergic disease compared to those without (2.84 (1.93 to 4.18) and 1.26 (0.8 to 1.98), respectively). Adjustment for parental allergy did not change markedly the association between obesity and wheeze, neither in boys (change from 1.95 to 2.02) nor in girls (1.51 to 1.47).
Conclusions Effect modification but no confounding by parental allergy could indicate that parental allergy does not stand for a common preceding cause of BMI and wheeze (eg, a common genetic pathway), but rather suggests that the influence of BMI may depend on the genetic/family background and also differ between boys and girls.
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