Obesity and Asthma

Vol. 17 •Issue 10 • Page 17
Obesity and Asthma

Researchers Look at Gender Differences

Evidence is mounting that America’s rising rates of obesity and asthma are not coincidental. They suggest a causal link. But does the link, if valid, hold for both men and women? Research varies.

A 1999 Harvard Medical School study found a definite obesity—asthma link among nearly 86,000 subjects, but the subjects were all women. The author insists his findings hold for men too. However, a 2001 Canadian study of both sexes found that obese women—but not men—were more likely to develop asthma than thinner women.

In the 1999 prospective study of 85,911 female American nurses, published in the Archives of Internal Medicine, asthma risk increased by as much as 2.7 times with increasing body mass index (BMI).

“Our work was the first prospective data showing an association between these two conditions,” said Carlos Camargo, Jr., DrPH, MD, associate professor of medicine at Massachusetts General Hospital in Boston.

The study was met with “widespread skepticism,” he said, “with a few exceptions who were very excited by the finding and immediately recognized we had hit on something very important.”

His team and others “have replicated our initial finding,” Camargo said. “Furthermore, a few groups have done small clinical trials that show that weight loss improves asthma severity.”

Camargo is convinced there is a causal link. “In some people, obesity causes asthma,” he declared. “Why? The exact mechanism is uncertain, but it probably has something to do with not taking deep breaths, with this leading to more reactive airways and, if bad enough, asthma.”

Regarding his all-female study cohort, Camargo noted that “in other databases, we and others have found that the finding holds in men.”

CDC Questionnaire

A major study the following year seemed to confirm that obese men, too, run an increased risk of asthma.

Kathryn Held, then a doctoral candidate in medical anthropology at the University of Oklahoma in Norman, crunched data from questionnaires given to 12,000 men by the Centers for Disease Control and Prevention from 1982 to 1994.

Dividing the data into four groups according to the men’s BMIs, Held found that the percentage of men having asthma rose as the groups proceeded from thinnest to heaviest: 5.30 percent, 8.09 percent, 8.93 percent and 17.31 percent.

But in 2001, Canadian investigators reported something quite different to the Congress of Epidemiology. While obese wo.men have almost double the risk of developing asthma compared with women of normal weight, that link does not apply to men, they said.

Yue Chen, PhD, and colleagues at the University of Ottawa tracked new cases of asthma among 4,266 men and 4,883 women over two years. Independent of age, women with a BMI of at least 30 kg/m2 were about twice as likely to develop asthma as women with a normal BMI. In contrast, obese men were not significantly more likely to develop asthma than normal-weight men.1

Male Inaccuracies

Chen said the data are “consistent” with previously reported data in which obesity was associated with a higher risk of asthma in Canadian women but not in men.

Reaction to the study “was positive and others have similar findings,” co-author Robert Dales, MD, told ADVANCE. Dales added that in follow-up studies, “we looked at the incidence of asthma and it also increased in overweight women but not in men.”

Asked to explain the Canadian finding, Camargo said: “I think part of the explanation is that women report their heights and weights more accurately than men.”

Camargo offered as evidence a cross-sectional analysis of 961 Mexican adults he studied in 2003. His team compared both measured BMI and self-reported BMI as risk factors for asthma. It found that measured BMI revealed a link between obesity and asthma for both men and women, while self-reported BMI revealed a link only in the women.2

“Therefore, misclassification of BMI ob.scured the relationship between obesity and asthma to a greater extent among men than among women since obesity prevalence Éwas higher among men,” Camargo et al. concluded. “Measurement bias merits greater attention in future research on obesity and asthma.”


1. Chen Y, Dales R, et al. Obesity may in.crease the incidence of asthma in women but not in men: longitudinal observations from the Canadian National Population Health Surveys. Am J Epid. (2002;155(3): 191-197).

2. Santillan A, Camargo C. Body mass index and asthma among Mexican adults: the effect of using self-reported vs measured weight and height. Int J Obesity (2003;27: 1430-1433).

You can reach Michael Gibbons at [email protected].