NEW YORK -- People who had used marijuana in the past month had smaller waists and lower levels of insulin resistance - a diabetes precursor - than those who never tried the drug, in a new study.
The findings, based on surveys and blood tests of about 4,700 U.S. adults, aren’t enough to prove marijuana keeps users thin or wards off disease. And among current pot smokers, higher amounts of marijuana use weren’t linked to any added health benefits, researchers reported in The American Journal of Medicine.
"These are preliminary findings," said Dr. Murray Mittleman, who worked on the study at Beth Israel Deaconess Medical Center in Boston.
"It looks like there may be some favorable effects on blood sugar control, however a lot more needs to be done to have definitive answers on the risks and potential benefits of marijuana usage."
Although pot smoking is a well-known cause of "the munchies," some previous studies have found marijuana users tend to weigh less than other people, and one suggested they have a lower rate of diabetes. Trials in mice and rats hint that cannabis and cannabinoid receptors may influence metabolism.
The new study used data from a national health survey conducted in 2005-2010. Researchers asked people about drug and alcohol use, as well as other aspects of their health and lifestyle, and measured their insulin and blood sugar levels.
Just under 2,000 participants said they had used marijuana at some point, but not recently. Another 600 or so were current users - meaning they had smoked or otherwise consumed the drug in the past month.
Compared to people who had never used pot, current smokers had smaller waists: 36.9 inches versus 38.3 inches, on average. Current users also had a lower body mass index - a ratio of weight to height - than never-users.
When other health and lifestyle measures were taken into account, recent pot use was linked to 17 percent lower insulin resistance, indicating better blood sugar control, and slightly higher HDL ("good") cholesterol levels.
However, there was no difference in blood pressure or blood fats based on marijuana use, Mittleman’s team found.
Mittleman said that in his mind, it’s still "preliminary" to say marijuana is likely to be responsible for any diabetes-related health benefits.
"It’s possible that people who choose to smoke marijuana have other characteristics that differ (from non-marijuana smokers)," and those characteristics are what ultimately affect blood sugar and waist size, he told Reuters Health.
Dr. Stephen Sidney from the Kaiser Permanente Division of Research in Oakland, California, said he wonders if cigarette smoking may partially explain the association. Marijuana users are also more likely to smoke tobacco, he told Reuters Health.
"People who use tobacco oftentimes tend to be thinner," said Sidney, who has studied marijuana use and weight but didn’t participate in the new study. "So I really wonder about that."
Another limitation with this and other studies, Sidney and Mittleman agreed, is that all of the data were collected at the same time, so it’s unclear whether marijuana smoking or changes in waist size and blood sugar came first.
"The question is, is the marijuana leading to the lower rate (of diabetes) or do they have something in common?" said Dr. Theodore Friedman, who has studied that issue at Charles R. Drew University of Medicine and Science in Los Angeles.
He and his colleagues think the link is probably causal. "But it’s really hard to prove that," Friedman, who also wasn’t involved in the new research, told Reuters Health.
One possibility is that the anti-inflammatory properties of marijuana help ward off diabetes, he said. But he agreed that more research is needed to draw out that link.
"I want to make it clear - I’m not advocating marijuana use to prevent diabetes," Friedman said. "It’s only an association."