Cause-and-Effect Relationship Between Obesity and Asthma Established

Key Point

Asthma incidence increases by 50% in overweight and obese individuals in a dose-response fashion. Sex does not appear to significantly affect the relationship.

NEW ORLEANS—Obesity should be added to the definitive list of risk factors for asthma, recommended researchers in the April 1 American Journal of Respiratory and Critical Care Medicine, as overweight and obese individuals were found to have at least a 50% increased risk. Earlier studies have revealed a modest link between increased weight and asthma incidence, though results from those studies did not preclude that asthma could instead contribute to obesity, due to inactivity or side effects of systemic corticosteroids.

David A. Beuther, MD, Assistant Professor of Medicine, and E. Rand Sutherland, MD, MPH, Medical Director of the Pulmonary Physiology Unit, both at the National Jewish Medical and Research Center in Denver, conducted the meta-analysis. The investigators searched for prospective studies that examined the incidence of asthma as stratified by BMI in adults followed for at least one year. A total of 333,102 unique subjects (74% women) from seven studies were included in the analysis, and all study populations included were well-characterized cohorts in the United States, Canada, and Europe, said the authors. Additionally, “All included studies were observational and of similar design; thus quantitative measures of quality were not used to weight the studies in the meta-analysis,” they said.

The summary odds ratio (OR) for one-year incident asthma in overweight (BMI between 25 and 30) and obese (BMI of 30 or greater) participants, when compared with participants of normal weight (BMI less than 25), was 1.51. A dose-response effect was also observed, as the OR of incident asthma increased significantly from 1.38 to 1.92 in overweight and obese individuals, respectively. However, contrary to findings from prior studies, sex did not appear to be a significant modifier of the relationship: Overweight or obese men had a slightly lower OR for one-year asthma than did overweight or obese women (1.46 vs 1.68), although the difference was insignificant. The dose-response relationship remained when the participants were stratified by sex.

Drs. Beuther and Sutherland said that their findings, when applied to the population of the United States as a whole, indicate that many people are at considerable modifiable risk for asthma: If 12% of overweight Americans plus an additional 6% of the nonoverweight population already have asthma, then “approximately 200 million United States adults are free of asthma but at risk of developing it,” they said. “If significant weight loss could be achieved … the number of new asthma cases in United States adults might fall by as much 250,000.” Cases of pediatric asthma, which are estimated as five times greater, could be significantly affected by even small changes in mean population BMI, they said.

The increased risk for asthma may in fact be underestimated, noted the authors. In three of the seven studies in the meta-analysis, participants with a BMI of less than 20 were included in the “normal-weight” group, even though being underweight has been shown as a risk factor for asthma. This could have elevated the normal-weight group’s asthma incidence and diminished the relative odds of asthma due to obesity, they said.

The authors noted that BMI may not be the most accurate measure of body fat, as it does not take into account sex differences in muscle mass and body fat distribution. While measures of abdominal adiposity have proved to be a better predictor of alteration in pulmonary function, said Drs. Beuther and Sutherland, BMI is still the most commonly used measure of obesity in the medical literature, and therefore was the most practical measure for the meta-analysis.           

—Jessica Dziedzic

Reference
Beuther DA, Sutherland ER. Overweight, obesity, and incident asthma: a meta-analysis of prospective epidemiologic studies. Am J Respir Crit Care Med. 2007;175:661-666.

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