Summarized by Robert W. Griffith, MD
November 7, 2005
Introduction
Physicians have noticed a correlation between the occurrence of obesity and allergies in women, but not in men. Scientists from New Hampshire have now studied how often, and why, it occurs. Here's a summary of their findings, which were published in the
American Journal of Clinical Nutrition.
First, a note on 'atopy'. Atopy is a hereditary tendency to develop immediate allergic reactions to substances such as pollen, food, dander, and insect venoms and displayed by hay fever, asthma, or similar allergic conditions. It's diagnosed by a raised level of immunoglobulin E (IgE) antibodies to allergens. And some factors can increase the development of atopy - vaccines, antibiotics, and, possibly, the promotion of a pathogen-free environment.
The main results of atopy can be asthma, eczema, and allergic rhinitis. It's therefore important to determine all the possible factors that increase atopy. The major female sex hormone, 17 -estradiol, is one of these. The possible relationship between obesity and allergies provides another area where such a factor may be discovered.
What was done
Twenty-one obese and 22 non-obese women aged 18 to 41 were studied. In the obese women, their fat mass (FM) comprised 30% or more of their body weight. The non-obese women had an FM below 30%.
IgE antibodies (both total and specific antibodies to selected common allergens) were determined, along with blood glucose, serum insulin, and plasma 17 -estradiol. An oral glucose tolerance test was used to determine insulin sensitivity. Interleukin-4 (IL-4) was also measured as an indicator of the activity of 17 -estradiol in increasing atopy.
What was found
The average FM of the obese group was 35%, and that of the non-obese women 23%. Their average BMI scores were 26.6 and 21.1, respectively. The average age overall was 21.5.
Although the total IgE antibodies were similar in both groups, the specific IgE antibodies were increased in three times as many women from the obese group - 12 of 21 vs. 4 of 22 women, respectively. Plasma 17 -estradiol and insulin resistance levels were increased in the obese, compared with the non-obese women.
What the findings mean
In this study 62% of the obese women, compared with 28% of those who were not obese, tested positive for atopy, and were therefore more likely to develop allergic disorders. The corresponding increased 17 -estradiol levels found suggest the effect is related to the synthesis of estrogens by fat tissue. Raised insulin resistance was also seen in the obese women, as expected, but its role in the occurrence of atopy is uncertain.
The prevalence of asthma has increased over 50% in the US since 1980, and is seen more often in adolescent and adult females than in males. Obesity has also increased at an alarming rate. It would seem that, by preventing obesity, the likelihood of developing allergies would be reduced. The findings provide yet another good reason to fight overweight and obesity, by appropriate calorie control and exercise.
Source
- Elevated atopy in healthy obese women. VJ. Vieira , RAM. Ronan , WMR. Windt , TAR. Taglioferro , Amer J Clin Nutr, 2005, vol. 82, pp. 504--509
