Heavy Cannabis Use Is Associated With Low Bone Mineral Density and an Increased Risk of Fractures

Purpose To investigate possible associations between recreational cannabis use and bone health in humans. Methods Cross-sectional study of individuals recruited from primary care in the UK between 2011 and 2013. Cases were regular smokers of cannabis divided into moderate (n = 56) and heavy user (n = 144) subgroups depending on whether they reported fewer or more than 5000 cannabis smoking episodes during their lifetime. Controls comprised 114 cigarette smokers. Results Heavy cannabis users had lower total hip bone mineral density (mean ± SD Z-score: −0.20 ± 0.9 vs +0.2 ± 0.9, P <.0005), lower spine bone mineral density (−0.5 ± 1.2 vs 0.0 ± 1.2, P <.0005), and lower body mass index (BMI; 26.5 ± 6.0 vs 29.0 ± 7.0, P =.01) than controls. Fracture rate was also increased in heavy users (rate ratio = 2.17; 95% confidence interval, 1.59-2.95; P <.001). When compared with controls, serum cross-linked C-telopeptide of type 1 collagen (CTX) concentrations were raised in heavy cannabis users (0.3 ± 0.1 vs 0.2 ± 0.1 pg/mL, P =.045), as were serum N-terminal propeptide of type 1 procollagen (P1NP) concentrations (47.1 ± 19.2 vs 41.2 ± 17.8 pg/mL, P =.01). Serum total 25-hydroxyvitamin D concentrations were reduced in heavy users compared with controls (25.3 ± 16.8 vs 36.9 ± 26.7 nmol/L, P = .002). Multiple regression analysis revealed that heavy cannabis use was an independent predictor of spine bone mineral density, accounting for 5.4% of the variance (P =.035), and total hip bone mineral density, accounting for 5.8% of the variance (P =.001), but mediation analysis suggested that the effect on spine bone mineral density was indirect and mediated through low body mass index. Conclusions Heavy cannabis use is associated with low bone mineral density, low BMI, high bone turnover, and an increased risk of fracture. Heavy cannabis use negatively impacts on bone health both directly and indirectly through an effect on BMI.