Studies Look At Relationship Between Asthma and Obesity

Obesity may increase the risk of asthma, suggest two new studies that were presented at the American Lung Association/American Thoracic Society International Conference in Chicago April 24-29, 1998. In one study, researchers using data from a study of more than 100,000 nurses found that the more overweight a nurse was, the greater her risk of developing asthma in adulthood. The second study found that the most overweight 26-year-olds were more likely to have asthma than the thinnest ones.

Obesity and Asthma
Obesity and asthma are both on the rise in developed nations. An estimated 14.6 million Americans, including 4.8 million children, suffer from asthma. Between 1982 and 1994, the rate of asthma rose 61%, while the rate of pediatric asthma rose 72%. According to the National Institutes of Health, one in three Americans is obese. Obesity is second only to smoking as a risk factor for disease, accountable for about 300,000 deaths per year.

Both of the studies set out to examine a possible relationship between obesity and asthma. Until now, it was commonly assumed that people with asthma may become overweight because their breathing problems limit their activity, according to Carlos A. Camargo, Jr., M.D., Dr.P.H., of the Harvard Medical School in Boston, who led the nurses study on asthma.

"But with proper treatment, people with asthma should not have activity limitations," he said.

In the nurses study, Dr. Camargo and colleagues used data from the women in the Nurses Health Study II, a prospective study of 116,678 female nurses. Of those nurses, they tracked the 89,061 who did not have asthma in 1991, and found that 1,652 developed asthma between 1991 and 1995. Those who were most obese in 1991 were three times as likely to develop asthma as those who were the least overweight.

In the second study, British researchers studied the relationship of birthweight, weight and height at age 26 to the prevalence of asthma in more than 8,000 people. The heaviest adults were 80% more likely to have asthma than the thinnest ones, according to researcher Seif O. Shaheen, Ph.D., of the United Medical and Dental Schools in London.

Before these studies very little research had yet been done to examine how obesity might lead to asthma, however, Dr. Camargo said it is possible that being overweight somehow compresses the airways, making them smaller and therefore more reactive to cold or other asthma triggers.

Dr. Shaheen offered several other possible explanations. One is that obese people tend to exercise less, and exercise may be directly beneficial to the lungs and prevent asthma. Another theory is that obese people may be more at risk because they eat a different type of diet.

The researchers in both studies measured subjects' obesity in terms of body mass index (BMI), a measure of how overweight someone is after taking into account their height. The higher the BMI the fatter the person; there are conventional cut-offs for "normal weight" (BMI 20-25), "overweight" (BMI 25-30) and "obese" (BMI>30).

Source: American Thoracic Society (ATS)

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