For overweight and obese individuals, the incidence of asthma increases by 50 percent, as compared to those of normal weight, according to a meta-analysis of seven studies on severe asthma involving 333,102 patients.
The results appear in the first issue for April 2007 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
E. Rand Sutherland, M.D., M.P.H., of the National Jewish Medical and Research Center in Denver, and one associate found a dose-dependent increase in the odds for asthma in overweight and obese men and women. Based on their results, the researchers suggest that asthma incidence could by reduced by targeted interventions against being overweight or obese.
According to the National Health and Nutrition Examination Survey (1999-2002), 65 percent of U.S. adults are either overweight or obese. "Although asthma is less prevalent than obesity, it affects approximately 7 percent of the adult population in the United States," said Dr. Sutherland, who noted that the odds of asthma incidence in overweight men and women were similar.
Asthma, a respiratory disease characterized by recurrent episodes of difficult breathing, wheezing, cough and thick mucus production, affected approximately 20.5 million Americans in 2004. Some common asthma triggers are allergic stimuli, infections, stress or strenuous exercise.
"If significant weight loss could be achieved in the population of overweight and obese individuals, it could be estimated that the number of new asthma cases in United States adults might fall by as much as 250,000 per year," said Dr. Sutherland. "If that decrease can be extrapolated to the pediatric population, where the annual incidence of asthma is as much as five times higher, the effect of even small changes in mean population body mass index may translate into significant decreases in asthma incidence in children and adults."
The researchers noted that obesity in the absence of asthma causes physiologic impairments in lung function, including reduction in lung volume, chest wall restriction and an increase in the oxygen cost of breathing. It also contributes to various other conditions including gastroesophageal reflux and sleep apnea. These difficulties can result in breathlessness (dyspnea) and wheezing, which might be mistaken for asthma by patients and clinicians.
"Weight loss studies have shown improvements in lung function and asthma symptoms, but not necessarily in airflow obstruction or airway hyperresponsiveness," said Dr. Sutherland. "It is also reasonable to believe that some of the patients with "asthma" may have respiratory symptoms due to obesity but may not meet rigorous objective physiologic criteria for asthma."
The authors concluded that obesity is a well-established risk factor for diabetes, sleep apnea, stroke, cardiovascular disease, arthritis and other illnesses. They said their findings support the addition of asthma to that list.