Review and feature articleThe epidemiology of obesity and asthma
Section snippets
Cross-sectional studies
Numerous, but not all, cross-sectional studies in different countries show an excess of obesity among adults with asthma compared with those without asthma.5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 Most of these studies used self-reported asthma, whether diagnosed by a physician or not. Furthermore, all studies used body mass index as the principal anthropometric measure, although there was some variability in how categories of body mass index were created.
Prospective studies
The results of 8 prospective studies that have reported on whether excess weight raises the risk of asthma development in adults are shown in Table I.9, 16, 18, 45, 46, 47, 48, 49, 50 Among 6420 participants in the 1970 British Cohort Study, of whom 714 reported having asthma at age 26 years, body mass index at age 10 years was not significantly associated with asthma at age 26 years.45 Birth weight was inversely associated with incident asthma in this study. In the Nurses' Health Study II, of
Weight-change studies
In at least 4 of the prospective studies conducted among adults, the effect of weight change on the future risk of incident asthma was examined. In the Nurses' Health Study, increases in self-reported weight strongly predicted asthma incidence.46 In the Coronary Artery Risk Development in Young Adults study, participants in the highest quintile of change in body mass index showed an increased risk for asthma development when compared with participants in the second quintile of change in body
Weight-loss studies
If excess weight does cause asthma, then weight loss could be expected to have the opposite effect or at least improve the clinical status of patients with asthma. Thus studies that examine the effect of weight loss in overweight and obese persons with asthma on the status of their disease could provide critical evidence that excess weight could be causally related to asthma. The results from bariatric surgery show impressive improvements in the clinical status of many morbidly obese patients
Discussion
The issue of whether the increase in obesity has caused an increase in the incidence and prevalence of asthma has been controversial. The results from cross-sectional, case-control, prospective, and weight-loss studies in the aggregate provide tantalizing, although inconclusive, evidence in support of a causative role of excess weight in the onset of asthma in adults. Prospective studies conducted among adults are fairly consistent in finding that excess weight is associated with asthma. Of the
Sex, obesity, and asthma
Whether the relationships between excess weight and asthma differ by sex has elicited a great deal of discussion. In adults one of the first prospective studies of obesity and asthma incidence was conducted in women, perhaps setting the stage for the debate.46 In a subsequent study from the Coronary Artery Risk Development in Young Adults Study, change in body mass index was significantly associated with asthma incidence among women but not among men.16 When a Canadian prospective study showed
Effect of obesity on patients with asthma
At least in the United States, large population-based surveys have shown since the 1970s that the prevalence of obesity among persons with self-reported asthma is considerably higher than that among persons without this condition.97 Cross-sectional studies are subject to the methodologic limitations outlined above, however. Thus the case definition of asthma in many surveys is based on self-report, often of a physician's earlier diagnosis. In some studies body mass index is based on
Conclusions
Although a considerable number of studies using different study designs indicate that excess weight might increase the risk of asthma development, the topic remains controversial because of potential methodological limitations inherent in many of these studies.106 Given the trends in the prevalence of obesity and asthma, clarifying this still opaque area is of considerable urgency, because if a consensus was to be reached that obesity indeed causes asthma, new options for preventing and
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Series editor: Harold S. Nelson, MD
Disclosure of potential conflict of interest: E. S. Ford—none disclosed.