Jun Ma, M.D., Ph.D., PAMF Research Institute
Do allergies and insulin resistance play a part in rising incidence of obesity and asthma in the U.S.? Researchers at the Palo Alto Medical Foundation Research Institute (PAMFRI) recently completed analysis of national survey data and found no evidence that either insulin resistance or atopy (allergies) plays a role in the relationship between obesity and asthma.
The results, published online prior to print in the journal Allergy, are from an analysis of the National Health and Nutrition Examination Survey (NHANES), an on-going, population-based national survey conducted by the Centers for Disease Control and Prevention’s National Center for Health Statistics.
“Obesity is a known risk factor for developing and living with asthma, and atopy and insulin resistance are two of several hypothesized, yet unproven, mechanisms that may explain the obesity-asthma relationship,” said Jun Ma, M.D., Ph.D., who led the analysis by the department of Health Services Research at the PAMFRI. “Atopy is a major risk factor for asthma. Obesity and insulin resistance are closely related. Unfortunately, data supporting these hypotheses are limited so we were highly motivated to investigate the role of atopy and insulin resistance as potential mechanisms.”
The investigation joins a small number of international studies as the first known population-based U.S. analysis aimed at exploring the potential explanatory roles of atopy and insulin resistance in the relationship between obesity and asthma. Data for the analysis came from the 2005-2006 NHANES survey of 10,348 people of all ages. The analysis included 4,493 adults (2,337 women and 2,156 men) aged 20 years and older who had completed the NHANES interview, representing nearly 200 million Americans. Their height, weight and weight circumference were measured. Additionally, they were tested for insulin resistance and specific IgE allergens (IgE, immunoglobulin E, are antibodies in the immune system) including dust mites, animal danders, fungi, grasses and trees.
In the study group, eight percent of participants had asthma; 67 percent were overweight or obese. The prevalence of atopy (allergies) was 41 percent, and incidence of insulin resistance was 22 percent.
The analysis showed no apparent role of either insulin resistance or atopy in the obesity-asthma relationship. Obesity was related to both atopic and non-atopic asthma (atopic asthma is also called allergic asthma and is a type of asthma that is triggered by allergens). Obesity’s relationship to asthma was independent of insulin resistance status. No association of obesity was observed with atopy. Further, insulin resistance was not related to asthma prevalence regardless of obesity status.
Dr. Ma cautioned that although the findings did not provide evidence of a possible role of atopy or insulin resistance linking obesity and asthma, additional research is necessary to confirm the lack of association. She noted that NHANES participants are interviewed only once and not followed over time and confounding by factors other than those being studied is always a potentially major problem in observational studies.
“The NHANES is a valuable data source for exploring different hypotheses but it is designed to provide a ‘snap shot’ of health, which inherently limits the ability to understand how and why diseases and medical conditions develop,” she said. “Therefore, the findings should be confirmed by additional and more rigorous studies, such as prospective cohort studies and intervention trials. Other potential mechanisms should also be explored, including obesity’s effects on the mechanics of breathing and airway inflammation, and the influences of common genetic pre-dispositions and lifestyle factors.”
Dr. Ma was assisted by her PAMFRI colleagues Lan Xiao, Ph.D., and Sarah Knowles, Ph.D.
The article has been published on-line ahead of print in the journal Allergy. To view the document online, a reader can access the article via PubMed: http://www.ncbi.nlm.nih.gov/pubmed/Pub Med ID: 20456316
The citation is: Ma J, Xiao L, Knowles SB. Obesity, insulin resistance and the prevalence of atopy and asthma in US adults. Allergy 2010; DOI:10.1111/j.1398-9995.2010.02402.x.
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