Physical activity and incident asthma in adults: the HUNT Study, Norway

OBJECTIVE: We aimed to investigate the associations of physical activity and change in physical activity with incident asthma in a cohort of Norwegian adults. DESIGN: We conducted a prospective cohort study using data on self-reported physical activity from 3 waves of the Nord-Trøndelag Health Study. Physical activity was reported at the first and second surveys (1985–1986 and 1995–1997). Physical activity was defined from the second survey as inactive or active and the active group was further defined as very low, low, moderate and high. Change in physical activity was defined from the first and second surveys. SETTING: A large population-based health survey in Norway. PARTICIPANTS: We followed 18 894 adults over 11 years who were free from asthma at baseline in 1995–1997. OUTCOME: Incident asthma was reported in the third survey (2006–2008). RESULTS: The cumulative incidence of asthma was 3.6% over the 11 years. The adjusted OR for incident asthma among active participants compared with inactive participants was 0.95 (95% CI 0.69 to 1.34). The adjusted OR for those who were active in the first or second survey versus those who were inactive in both surveys was 0.64 (95% CI 0.34 to 1.38); however, this association was strongly attenuated in sensitivity analysis (OR 0.93, 95% CI 0.38 to 3.09). CONCLUSIONS: We did not observe statistically significant associations of physical activity or change in physical activity with incident asthma in adults over the 11-year follow-up.