Background: Inadequate milk consumption and being overweight are each associated with asthma symptoms in children. Milk consumption has been inversely related to childhood overweight. Thus, being overweight may be a pathway or a confounder in milk-asthma relationship. A combination of both factors may be associated with greater risk of asthma than one factor alone.
Methods: This study included 246 children with allergist-diagnosed asthma and 477 nonasthmatic controls at the age of 8-10 years. Information on milk consumption during the last 12 months was obtained from questionnaires. Being overweight was defined as body mass index > or =85th percentile. Being overweight as a possible pathway or confounder was formally tested. The odds ratio (OR) for combined infrequent milk consumption and being overweight in asthmatic vs nonasthmatic children was determined in multivariate logistic regression analyses.
Results: There was a significant interaction between milk consumption and sex of the child in relation to asthma. Asthma was significantly associated with infrequent milk consumption in girls (crude OR 2.11, 95% CI 1.05-4.24) but not in boys. The asthma-milk relation in girls was neither mediated by being overweight (p(mediation tests) = 0.27) nor was the relationship confounded by being overweight (a 9% change in coefficient). Asthmatic girls had 3.6 times increased odds of having combination of infrequent milk consumption and being overweight than nonasthmatic girls (adjusted OR 3.64, 95% CI 1.18-11.24). Asthma was not associated with either factor or with absence of the other in girls.
Conclusion: Infrequent milk consumption plus being overweight may have great risk for asthma in girls.