A longitudinal study of the effects of tobacco and cannabis exposure on lung function in young adults

Aim To assess the possible effects of tobacco and cannabis smoking on lung function in young adults between the ages of 18 and 26. Setting and participants A group of over 900 young adults derived from a birth cohort of 1037 subjects born in Dunedin, New Zealand in 1972/73 were studied at age 18, 21 and 26 years. Measurements Cannabis and tobacco smoking were documented at each age using a standardized interview. Lung function, as measured by the forced expiratory volume in one second/vital capacity (FEV1/VC) ratio, was obtained by simple spirometry. A fixed effects regression model was used to analyse the data to take account of confounding factors. Findings When the sample was stratified for cumulative use, there was evidence of a linear relationship between cannabis use and FEV1/VC (P