THURSDAY, April 5, 2007 (HealthDay News) -- Overweight and obese individuals are 50 percent more likely to develop asthma than normal-weight men and women, new research suggests.
Public health efforts to control asthma should therefore emphasize the importance of healthy weight management, the researchers argue in the April issue of the American Journal of Respiratory and Critical Care Medicine.
"The bottom-line is that being overweight appears to significantly increase the risk of asthma," said study co-author Dr. E. Rand Sutherland, of the National Jewish Medical and Research Center (NJMRC) in Denver. "But the caveat is, that until further studies are done, it won't be clear exactly what type or severity of asthma is present in obese people."
According to the U.S. National Institutes of Health, asthma is an incurable but usually controllable chronic disease involving inflammation and narrowing of the airways that carry oxygen into and out of the lungs.
The disease typically provokes recurrent wheezing, coughing, and a hypersensitivity to allergies and affects approximately 20 million Americans, including 9 million children.
A recent national survey found that about 65 percent of Americans are either obese or overweight, and research has long suggested links between asthma and obesity.
In this study, Sutherland and NJMRC colleague Dr. David A. Beuther pored over prior data on the body mass indices -- measurements of body fat based on the height and weight -- of adult asthma patients.
They looked at data from seven prior studies conducted between 1966 and 2006 in the United States, Canada, and Europe. Together, these studies had looked BMI and asthma in more than 333,000 severely asthmatic patients.
During data review, Sutherland and Beuther adopted standard BMI yardsticks, which define "normal weight" as having a BMI of under 25, "overweight" as a BMI between 25 and 29, and "obese" as a BMI more than 30. For example, a person who is 5 feet 6 inches tall and weighs 145 pounds has a BMI of 22.
The odds of developing asthma grew by 50 percent among patients with a BMI of 25 and up, and the risk climbed as the pounds piled on, the study found.
Women and men appeared to be equally susceptible to the weight-asthma association, they added.
Based on the findings, the researchers believe asthma should be added to the long list of diseases -- including diabetes, sleep apnea, stroke, cardiovascular illness, and arthritis -- for which excess weight is a risk factor.
And because two-thirds of the U.S. adult population are now thought to be obese or overweight, that means millions more Americans may be at risk of developing asthma than was previously thought, they said.
On the up side, "significant weight loss" could potentially reduce asthma cases by as many as 250,000 each year, the researchers said.
Not every overweight person with respiratory symptoms necessarily has asthma, however. The experts noted that excess weight can cause lung volume reduction, chest wall restriction, and breathlessness unrelated to the disease.
"If you're overweight, and you have respiratory symptoms, you don't need to jump to the conclusion that you have asthma," said Sutherland. "But, of course, it would probably be appropriate to have those symptoms further evaluated."
Dr Norman H. Edelman is chief medical officer for the American Lung Association and professor of preventive medicine and medicine at Stony Brook University in Stony Brook, N.Y. He said the findings regarding gender were most interesting.
"There's a lot of work that suggested the [obesity] effect was there in women and not in men," he said. "Certainly, in terms of my own clinical practice, I see people -- men and women -- with asthma that's difficult to manage, and many of them are overweight. But for men, it's something that wasn't clear before, and that's why this analysis is valuable."
But he agreed that proving cause and effect is tricky.
"The problem with asthma is that, unlike many other diseases, it's not like flipping a switch. It's not that you have it or don't have it. There are a lot of people walking around with a little bit of asthma, and they don't even know it," Edelman said. "So, it's not clear if obesity is actually causing the disease or perhaps converting a pre-existing undiagnosed asthma into a severe asthma. So, I don't know if I would say that obesity causes asthma. But certainly, it's a risk factor for clinically significant asthma."
For more on asthma, visit the U.S. National Institutes of Health.