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 Asthma and Obesity: A Tangled Twosome
 To figure out whether asthma is associated with obesity in Oregon, we looked at asthma status by body mass index (BMI) among Oregonians.3
Increased BMI was associated with increased prevalence of asthma in the general population. However, the results become even more striking when we consider men and women separately. In women, the asthma prevalence was 1.8 times higher in overweight women, 3.2 times higher in obese women, and 7.5 times higher in extremely obese women compared to normal weight (Figure 2). All results were statistically significant (p <.05).Among men, those in the obese group had 1.9 times higher asthma prevalence (p <.05) compared to the normal weight group, but prevalences for the overweight and extremely obese groups were not significantly different.
Many studies have found that asthma and obesity are associated; most found the association in women only.The majority of studies have looked at people at one point in time, so it is not possible to tell whether the asthma or the obesity came first. However, two recent studies that followed large groups of adults for a number of years clarify this issue. They looked at groups of obese and normal weight individuals who did not have asthma at the start, and monitored for development of asthma. One study was among women only, and the other included men too.The study that included men did not find an increased risk of asthma in obese men. Conversely, the risk of developing asthma was two to four times higher in obese compared to normal weight women. In fact, one study showed that women who had gained 22 pounds or more since age 18 had 1.4 to 2.5 times the risk of developing asthma during the study period (p for trend <.001). Because these women did not have asthma at the start of the study, having asthma could not have caused their obesity.
These studies reveal that, for women, as BMI increases so does the likelihood of developing asthma. These data alone are not sufficient to prove that obesity causes asthma, but suggest the possibility of a causal relationship in women.
3. We conducted simple logistic regression to estimate the odds ratio (OR) of having asthma based on BMI category, using normal weight as the reference category.
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