People who regularly smoke large amounts of marijuana may be more susceptible to bone fractures than people who don't use the drug, according to a new study conducted in the United Kingdom.
Researchers also found that the people in the study who used marijuana regularly tended to have thinner bones than the people who did not use pot. Having thinner bones might put people at higher risk for osteoporosis, a condition in which a person's bones become brittle and fragile, the researchers said.
"Our research has shown that heavy users of cannabis have quite a large reduction in bone density compared with non-users, and there is a real concern that this may put them at increased risk of developing osteoporosis and fractures later in life," study co-author Dr. Stuart Ralston, a professor of rheumatology at the University of Edinburgh in Scotland, said in a statement.
In the study, the researchers looked at 170 people ages 18 and older who smoked marijuana regularly and 114 people who had never used the drug. All of the participants were patients at a single, general-practice health facility in the U.K., according to the study, which will be published in an upcoming issue of The American Journal of Medicine. [Marijuana Could Treat These 5 Conditions]
The researchers asked the participants if they used marijuana or any other drugs, and whether they had ever had a fracture. The researchers also asked the people about their diets, to see how much calcium they consumed. (Calcium has been shown to play a role in bone health.) The researchers also measured the people's bone densities with X-ray tests.
It turned out that the people who had smoked marijuana on 5,000 or more occasions in their lives had 5 percent lower bone density than those who had never smoked pot. Moreover, the regular marijuana users had experienced more fractures throughout their lives, on average, compared with the people who had never used marijuana, the researchers found.
The findings suggest that there may be a link between heavy marijuana use and thinner bones, but they do not prove that smoking marijuana causes bones to become thinner, said Dr. Matthew Hepinstall, an orthopedic surgeon at Lenox Hill Hospital Center for Joint Preservation and Reconstruction in New York City who was not involved in the study. [11 Odd Facts About Marijuana]
The authors of the new study found that "factors such as age and body mass index [BMI] had much larger effects on bone mineral density than cannabis in this clinical study," Hepinstall noted.
The researchers said they don't know for sure how the link between marijuana use and lower bone density might be explained. But they also observed that the people who used marijuana a lot tended to have lower BMIs than those who did not use the drug. Having a lower BMI might make these people's bones more prone to thinning, the researchers said.
The new study "builds on prior animal research demonstrating complex interactions between cannabinoid receptors," which mediate the many effects that cannabis has on body cells and activity of bone cells, Hepinstall told Live Science.
For example, one previous study conducted in mice suggested that CBD (cannabidiol), one of marijuana's compounds, might actually help to heal fractures. However, it is not clear whether the findings of that study would apply to humans.
Originally published on Live Science.
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