Rising prevalence of asthma is sex-specific in a US farming population

Background: Asthma prevalence is increasing worldwide in most populations, likely due to a combination of heritable factors and environmental changes. Curiously, however, some European farming populations are protected from asthma, which has been attributed to their traditional lifestyles and farming practices. Objective: We conducted population-based studies of asthma and atopy in the Hutterites of South Dakota, a communal farming population, to assess temporal trends in asthma and atopy prevalence and describe the risk factors for asthma. Methods: We studied 1325 Hutterites (ages 6-91 years) at 2 time points from 1996 to 1997 and from 2006 to 2009 by using asthma questionnaires, pulmonary function and methacholine bronchoprovocation tests, and measures of atopy. Results: The overall prevalence of asthma increased over the 10- to 13-year study period (7.5%-11.1%, P =.049), whereas the overall prevalence of atopy did not change (45.0%-44.8%, P =.95). Surprisingly, the rise in asthma was only among females (5.8%-11.2%, P =.02); the prevalence among males remained largely unchanged (9.4%-10.9%, P =.57). Atopy, which was not associated with asthma risk in 1996 to 1997, was the strongest risk factor for asthma among Hutterites studied in 2006 to 2009 (P = .003). Conclusions: Asthma has increased over a 10- to 13-year period among Hutterite females and atopy has become a significant risk factor for asthma, suggesting a change in environmental exposures that are either sex limited or that elicit a sex-specific response.