A new study in the May 2009 Journal of Allergy and Clinical Immunology shows a possible correlation between childhood obesity and later development of atopic symptoms like hay fever, eczema, and food allergies. The study followed 4,000 children and found a clear relationship between BMI (body mass index) percentile and the amount of IgE -- the antibodies responsible for allergic reactions -- circulating in the bloodstream. In this study, the effect was strongest among girls.
What is far less clear, however, is why there should be a relationship between obesity and allergic status. Researchers considered the possibility that levels of C-Reactive Protein (CRP), a protein associated with inflammation, might be related to atopy. In this study there did seem to be higher levels of CRP in children with higher levels of BMI and higher levels of IgE and food allergies, but it is unknown at this time what the cause-effect relationships between these factors is. While this study covered a large population, the researchers caution that different explanations for their findings -- including hormones, intestinal microbes, or some as-yet unknown factor -- may explain the differences among the children studied.
Visness, Cynthia M., et al. "Association of obesity with IgE levels and allergy symptoms in children and adolescents: Results from the National Health and Nutrition Examination Survey 2005-2006." Journal of Allergy and Clinical Immunology May 2009. 123(5): 1163-69.
