Obesity in children, teens may be linked to allergies

Obese children and adolescents are at increased risk of also having some kind of allergy, especially to a food. It remains unclear, though, which condition is causing the other, according to a study published online Feb. 23 in The Journal of Allergy and Clinical Immunology.

"The data ... doesn't prove causality, but it provides a suggestion that allergic outcomes may be related to obesity," said Cynthia M. Visness, PhD, a scientist with the contract research organization Rho Inc. in Chapel Hill, N.C. The study was funded by the National Institute of Environmental Health Sciences.

Researchers analyzed numbers from the 2005-06 National Health and Nutrition Examination Survey. Participants ages 2 to 19 with weight at the 95th percentile or greater were 26% more likely than those whose weight was normal to have high Immunoglobulin E antibody levels. The risk of having IgE specific to a food rose by 59%. C-reactive protein levels increased as IgE and weight escalated.

Several previous studies indicated that asthma and obesity are linked, and the authors of this paper are working with NHANES data to further investigate that relationship. Experts suggest the connection for allergies as well, because a great variety and amount of food eaten by those with excess weight may trigger production of IgE antibodies. When these antibodies combine with the inflammation produced by additional fat tissue, the situation may be ripe to develop one or more allergies.

"An obvious reason for obese persons to develop more allergies is they consume an increased quantity and variety of foods that are capable of stimulating the immune system towards allergy," said Sami Bahna, MD, DrPH, president-elect of the American College of Allergy, Asthma & Immunology.

"Also, the fat tissue produces increased leptin, which facilitates sensitization to protein allergens. Another factor is increased production of C-reactive protein, which is a marker of systemic inflammation and may enhance allergic inflammation." Dr. Bahna also is professor and chief of allergy and immunology at Louisiana State University Health Sciences Center in Shreveport.

Unanswered questions

Other experts and the authors expressed caution about this theory because this cross-sectional study does not prove which condition is the cause and which is the effect. The rates of both have grown over the past few decades, and another possibility is that foods people eat instead of the ones they are allergic to may predispose them to gain weight.

"If you think you are allergic to milk, what are you going to replace it with? Are you going to replace it with things that are bad for you?" asked Frank Greer, MD, chair of the American Academy of Pediatrics' Committee on Nutrition and professor of pediatrics at the University of Wisconsin School of Medicine and Public Health in Madison.

Questions also surround the magnitude of the effect of this relationship. The differences were statistically significant, but the confidence intervals came very close to one. Also, these two conditions may be connected but may not be each other's cause or effect. Some of the same factors implicated in the development of allergies, such as breastfeeding, also have been linked to obesity. This study may have detected an increased risk of two medical conditions that have common roots. In addition, it's possible to have high levels of IgE without actually having an allergy.

"This study was looking at allergic-specific IgE to foods, but that's not really how we diagnose food allergies. We correlate symptoms to positive IgE tests. There are predictive values, but it's not 'yes' or 'no' for a given food. I would not say that every child with an IgE to egg was allergic to eggs in reality," said Bradley A. Becker, MD, a spokesman for the American Academy of Allergy, Asthma and Immunology and associate professor at Saint Louis University School of Medicine.

No data suggest that losing weight can reduce the risk of developing allergies or reduce the symptoms once they have already developed, although experts believe this latest study suggests the need for more research.