The endocannabinoid system has important effects on bone mass and bone turnover. Mice with targeted inactivation of type 1 (CB1) and type 2 (CB2) cannabinoid receptors develop osteoporosis with increasing age raising the possibility that cannabinoid receptor agonists might protect against age-related bone loss. Since cannabis is the most widely used illegal drug and its main psychotropic component -Δ9-tetrahydrocannabinol (THC)- is an agonist at CB1 and CB2 receptors, we wanted to determine if there was an association between cannabis use and bone mineral density (BMD) in humans. The study comprised 109 regular cannabis users and 71 cigarette-smoking controls, prospectively recruited from the local community. Cannabis users were divided into two groups based on their lifetime exposure (joint-years) into moderate (0.0157) and heavy subgroups (58540). Cannabis users were younger than controls by about 10 years. Heavy users had a lower BMI (P=0.002) and lower fat mass on DEXA (P<0.001) compared to controls. They had substantially lower BMD Z-score values at the lumbar spine (P=0.047) and total hip (P=0.003) than controls with evidence of a dose effect such that heavy users had total hip Z-score values ~0.5 Z-score units lower than controls. A high proportion of heavy users were young men. There was no difference between users and controls in self-reported alcohol intake but heavy users smoked less tobacco (P=0.025) and had higher dietary calcium intake (P<0.001) than controls. Multivariate analysis showed that gender and BMI were the most important determinants of spine and hip BMD Z-score in the study cohort indicating that the negative effects of cannabis use on bone health might be due to an effect on BMI. We conclude that cannabis users have low bone mass at spine and hip, demonstrating that in people of this age, heavy cannabis use negatively impacts bone health.
18 May 2013 - 22 May 2013