Abstract
This BMedSc (Hons) thesis examined whether cannabis use was associated with two cardiovascular risk factors and if so, the extent and direction of this association. The specific outcomes examined were cardiorespiratory fitness and body mass index. The thesis begins with a systematic review of the literature related to cannabis use and adverse health outcomes in the context of the well known Bradford-Hill criteria for causation. The second chapter describes the sample and methods used in this thesis, specifically the Dunedin Multidisciplinary Health and Development Study, and data collected therein. The third chapter presents the results. In unadjusted analyses cannabis use (defined as lifetime 'joint-years' exposure) was negatively associated with both cardiorespiratory fitness (coefficient= -31.08; 95% CI= -19.72 to -42.43, p< 0.001) and Body Mass Index (BMI) (coefficient= -0.114; 95% CI= -0.184 to -0.051, p = 0.001). However, following adjustment for potential confounders there was no longer an association between joint-years and cardiorespiratory fitness at age 32 (coefficient= 11.73; 95% CI= -138.77 to 162.22, p = 0.78). There was a significant interaction between sex and joint-years for the BMI analyses, hence the data were analysed separately by sex. In contrast to the null findings for cardiorespiratory fitness, lifetime cannabis use appeared to be associated with a decrease in BMI among females that remained marginally significant after adjustment for a range of potential confounders including BMI at age 15, socioeconomic status in childhood and adulthood, pack-years of tobacco exposure, alcohol use in previous 12 months and parental BMI (coefficient = -0.16; 95% CI= -0.35 to 0.02, p = 0.087). Cannabis use was also negatively related to BMI among the males in the unadjusted model (coefficient = -0.09; 95% CI= -0.16 to -0.02 p = 0.016), but this relation was no longer significant after adjustment for confounders. Interestingly, among males there was a trend (p = 0.075) towards an interaction between cannabis and tobacco use. This was explored further by stratifying into two groups based on history of having ever used tobacco (Yes, No). Analyses revealed a significant negative association between cannabis use and BMI, but only among males who had used tobacco (coefficient = -0.16; 95% CI= -0.23 to -0.09, p < 0.001). The final chapter of the thesis reviews the strengths and weaknesses of the sample, measurements and analyses before discussing possible reasons and/or mechanisms for the associations observed. Implications of the findings for theory, research and practice are then considered.