Lifetime cannabis exposure and small airway function in a population-based cohort study

BACKGROUND AND OBJECTIVE: The long-term effects of cannabis on small airway function remain unclear. We investigated associations between cannabis use and small airway function in a general population sample. METHODS: Cannabis use was ascertained at multiple ages from age 18 to 45 years and quantified as joint-years among 895 participants in the Dunedin Multidisciplinary Health and Development Study. Small airway function at ages 38 and 45 years was measured using impulse oscillometry (IOS) before and after inhalation of salbutamol. Analyses used multiple linear regression adjusting for tobacco use, body mass index and height. Longitudinal analyses of cannabis use between 38 and 45 years also adjusted for IOS at age 38 years. RESULTS: Associations between lifetime cannabis joint-years and IOS differed between men and women: in women, cannabis use was associated with pre-bronchodilator resistance at 5 Hz (R(5)) and 20 Hz (R(20)), reactance at 5 Hz, area of reactance and resonant frequency, and marginally associated with the difference between R(5) and R(20). Cannabis use was only statistically significantly associated with pre-bronchodilator resonant frequency in men. Cannabis use between the ages of 38 and 45 years was associated with a similar pattern of changes in IOS measures. After salbutamol, cannabis use was only statistically significantly associated with R(5) and R(20) among women and none of the IOS measures among men. CONCLUSIONS: Cannabis use is associated with small airway dysfunction at age 45 years, indicating an increase in peripheral airway resistance and reactance. These associations were greater and mostly only statistically significant among women. Associations were weaker and mostly nonsignificant after bronchodilator use, suggesting that cannabis-induced changes in small airways may be at least partially reversible.