Asthma Puts Chokehold on the Overweight and Obese

DENVER, April 2 -- The occurrence rate of asthma increases by 50% in adults who are overweight or obese, according to a small meta-analysis.

Both men and women appeared equally affected, said E. Rand Sutherland, M.D., M.P.H., of the National Jewish Medical and Research Center here, and David A. Beuther, M.D., of the University of Colorado at Denver.

Previous studies have found obesity to be a risk factor for asthma, but there was wide variation in occurrence estimates and controversy on the role of gender.

Although the increased risk of incident asthma was modest over one year for both sexes, the odds "when multiplied over many years are likely to be clinically significant," the investigators wrote in the first April issue of American Journal of Respiratory and Critical Care Medicine.

Their meta-analysis included seven prospective observational studies that examined new-onset asthma in relation to body mass index (BMI) among a total 333,102 adults in the United States, Canada, and Europe.

For the analysis, the participants were classified as obese (BMI at least 30 kg/m²), overweight (BMI 25 to 29.9 kg/m²) or normal/underweight (BMI less than 25 kg/m²).

Among the annualized results, the researchers found:

• Overweight and obesity together increased the odds of incident asthma significantly compared with normal weight (odds ratio 1.51, 95% confidence interval 1.27 to 1.80).
• Overweight alone was associated with significantly higher odds of asthma onset (OR 1.38, 95% CI 1.17 to 1.62).
• Obesity alone was associated with even higher likelihood of incident asthma (OR 1.92, 95% CI 1.43 to 2.59).
• Obesity was more predictive of asthma onset than overweight (OR for obesity versus overweight 1.49, 95% 1.20 to 1.85, P<0.001), indicating a significant dose-response trend (P<0.0001 for trend).

The role of gender in this relationship has been controversial. Previous findings ranged from a link only among women to only among men.

However, the meta-analysis found a similar increase in asthma occurrence with obesity for both genders. The odds ratio was 1.46 for men and 1.68 for women with overlapping confidence intervals (95% CI 1.05 to 2.02 and 1.45 to 1.94, respectively, P=0.232 for comparison). An increase in occurrence with an increase in weight remained intact when stratifying by gender.

The researchers cautioned, though, that, even without asthma, obesity causes physiologic impairments in lung function including reduced lung volume and chest wall restriction.

"These can result in dyspnea and wheezing, which might be mistaken for asthma by patients and clinicians," they wrote.

"It is reasonable to believe that some of these patients with 'asthma' may have respiratory symptoms due to obesity but may not meet rigorous objective physiologic criteria for asthma," they added.

Furthermore, they noted that their study may have been limited by use of potentially biased self-reported heights and weights in many of the studies, and there was no data available on abdominal adiposity, which may be a better indicator of lung function than BMI.

Nonetheless, the researchers concluded that extra girth seems to be a risk factor for asthma, and added "if they can be considered to be modifiable risk factors, interventions that effect weight loss could be associated with a decrease in asthma incidence."

They estimated that significant weight loss in the overall U.S. population of overweight and obese individuals could drop the incidence of asthma among adults by up to 250,000 cases per year.

The findings "should provide yet one more piece of information to compel obese individuals to lose weight and to support the aggressive implementation of public health measures to support the attainment of this goal," they added.