Body mass index in young children and allergic disease: gender differences in a longitudinal study.

Background: The increase in allergic diseases has occurred in parallel with the obesity epidemic, suggesting a possible association.

Objective: We investigated the relationship of body mass index (BMI) up to age 8 years with allergic disease within a birth cohort.

Methods: Children were followed from birth and were reviewed at age 3, 5 and 8 years (n=731; male 406). Parents completed questionnaires; children were weighed, measured, skin prick tested and examined.

Results: Increasing BMI at 3, 5 and 8 years increased the risk of current wheezing at the corresponding age (odds ratio [95% confidence interval] per standardized deviation score: age 3, 1.26 [1.04-1.53], P=0.02; age 5, 1.33 [1.06-1.67], P=0.02; age 8, 1.27 [1.0-1.62], P=0.05). The effect of BMI on wheeze at age 8 years differed between boys and girls, with a significant positive association in girls, but not in boys (P=0.04 for interaction). The effect of BMI at earlier ages on current or subsequent wheezing did not differ significantly between genders. Increasing BMI significantly increased the risk of physician-diagnosed eczema at age 5 (1.23 [1.04-1.47], P=0.02) and 8 (1.23 [1.03-1.45], P=0.02), with a significant interaction between gender and BMI at age 5 (P=0.04). There was no association between BMI and sensitization. Being overweight at age 3 years was significantly associated with late-onset wheeze (3.83 [1.51-9.75], P=0.005), persistent wheeze (4.15 [2.07-8.32], P<0.001) and persistent eczema (1.79 [1.03-3.13], P=0.04) in both boys and girls.

Conclusions: Being overweight is associated with an increased risk of allergic disease in childhood. However, the strength of the association varies with the gender, age and atopic phenotype.