SAN FRANCISCO – Vitamin D deficiency may help explain why obese children are more at risk than others for allergies and asthma, according to an observational cross-sectional study.
"In our population, we found that the allergic profile was increased in obese adolescents," said lead investigator Dr. Candace Percival, a pediatric endocrinology fellow at the Uniformed Services University of the Health Sciences in Bethesda, Md.
Fifty-four boys and girls 10-18 years old who were at or above the 85th percentile for age- and sex-adjusted body mass index and 32 normal-weight controls participated in the project. The investigators tested for blood levels of vitamin D, immunoglobulin E (IgE), leptin, adiponectin, and cytokines that contribute to allergy and asthma.
Dr. Candace Percival
As expected, based on previous obesity studies, higher BMIs correlated significantly with higher leptin and lower adiponectin levels, both of which have been linked to enhanced allergic response. Obesity correlated significantly with increased levels of IgE, IL (interleukin)-6 and IL-13 as well; the obese subjects were all also vitamin D deficient.
However, "when we ran a multivariate analysis controlling for vitamin D deficiency, we found that the statistical significance of correlations between cytokines and IgE with BMI disappeared. The relationship between BMI and ... markers of allergic disease seemed to depend on vitamin D deficiency; it was a dependent cofactor for adolescents having this allergy profile. It’s hard to say if there’s any sort of causal relationship, [but] this makes us wonder if vitamin D may be a mediator of the increased risk for allergy in the setting of obesity," Dr. Percival said at the Endocrine Society’s annual meeting.
It’s not an unreasonable thought. "Past research has shown that vitamin D is important for normal immune system function. It has both anti-inflammatory and antiallergic effects. Vitamin D deficiency is very common in obese individuals [and] is associated with an increased risk for allergy and asthma; it may skew the immune system towards an allergic response," she said.
The next step is to see if vitamin D supplements make a difference in biochemical markers and symptoms of allergic response in obese adolescents. Dr. Percival said she hopes to initiate that trial.
The authors said they had no relevant financial disclosures. The study was funded by Walter Reed National Military Medical Center and the Diabetes Action Research and Education Foundation in Washington, D.C.