Ever get so high you can feel it in your bones?
That might not be a good thing.
People who smoke "heavy" amounts of pot have a lower bone density, lower body mass indexes (BMI), and an increased risk of breaking bones than do people who only smoke "moderate" amounts of pot, according to a study published in September in the Journal of the American Medical Association. ("Heavy" users are defined as those who have smoked at least 5,000 times over a lifetime, although the researchers note that the average "heavy" user had smoked 47,000 times over a lifetime.)
Using an x-ray technique, the researchers measured the bone densities of 170 British stoners and compared them with people who only smoked cigarettes. After statistically controlling for other factors, the "heavy" stoners had bones that were 5% less dense than the non-"heavy" groups.
"We have known for a while that the components of cannabis can affect bone cell function but we had no idea up until now of what this might mean to people who use cannabis on a regular basis," said Stuart Ralston, Ph.d., a lead researcher, in a press release from the University of Edinburgh.
The authors conclude in the paper: "Heavy cannabis use negatively impacts on bone health both directly and indirectly through an effect on BMI."
In some ways, this result isn't entirely surprising. Contrary to the popular image of stoners as lazy, overweight dudes, people who smoke pot every day actually tend to be thinner and have lower BMIs than non-smokers do. While smoking pot stimulates appetite in the short term, it doesn't necessarily stimulate weight gain in normal-sized people. And people who smoke pot tend to have a lower insulin resistance than those who don't, according to a 2015 study. (Important note: We're talking about correlation here, not causation. Don't start knocking down pot brownies because you think they'll make you skinnier.)
Still: While pot smokers don't necessarily fit the All-American jock stereotype, they're statistically a little bit healthier than the average joe, at least by these measures. And a 2015 study actually suggested that CBD, the naturally occuring cannabinoid in marijuana that isn't responsible for the high (that's THC's job), can heal bones both faster and stronger.
So what gives? One explanation could be purely biological: Just as astronauts lose bone density because their skeletons don't have to support as much weight, heavy pot smokers might suffer the same effects because of a reduced BMI, as the researchers point out. Less body mass to support means lighter bones. And over time, smoking huge amounts of pot could even supress one's appetite, translating to fewer nutrients to support healthy bones, the researchers say.
It's also worth pointing out that the study was statistically quite small—just 170 people—and that the distinction of "heavy" smoking somewhat arbitrary. And asking a bunch of stoners to remember exactly how many times they've smoked is probably a futile endeavor, so those estimates may not be entirely reliable.
Another possibility? People who spend this much time sitting around getting absolutely stoned—again, we're talking about smoking 47,000 times on average over a lifetime—aren't necessary spending all their time playing sports and working out, which have both been shown to increase bone density.
Bottom line? If you're worried about cracking your hip for the third time, maybe stop hitting the bong so often—or at least balance out that pot habit with strongman training or something.