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Both obesity and asthma have increased in prevalence in children in the UK and America in recent decades and it has been suggested that the two might be causally related. Now US data have confirmed an association between body mass index (BMI) and asthma but the authors of a British report have concluded that the increase in asthma is not explained by increased prevalence of overweight and obesity.
The US Third National Health and Nutrition Examination Survey of 1988–94 included 7507 children aged 4–17 years (E von Mutius and colleagues.
). The prevalence of asthma in successive increasing quartiles for BMI was 8.7%, 9.3%, 10.3%, and 14.9%. The association between asthma and BMI remained significant after adjustment for confounding factors such as exposure to tobacco smoke, birthweight, breast feeding, and household size. An association between BMI and atopy (positive skin prick test reactions) was no longer significant after statistical adjustment. It is suggested that overweight or obesity might contribute to asthma either through a mechanical effect on lung function or via a proinflammatory effect.
The National Study of Health and Growth in England and Scotland included about 3600 primary school children per year between 1973 and 1982 and about 5000 per year between 1984 and 1994 (Susan Chinn and Roberto Rona.
). Both asthma prevalence and BMI standard deviation score increased with time, more noticeably beginning in 1982, but for both sexes the odds ratio per year for asthma (1.09) was the same before and after adjustment for BMI.
There is a positive association between BMI and asthma prevalence but the recent increase in asthma prevalence is not explained by increases in body weight. Similar environmental or lifestyle changes may have affected both asthma and obesity.