Study linking cardiovascular death and marijuana far from conclusive

By Lynne Terry

Marijuana may be bad for your heart.

A new study released late Tuesday indicates a possible link between marijuana use and death caused by cardiovascular disease.

The research is preliminary and comes with caveats. But it marks an attempt to analyze a possible connection between marijuana use and heart disease following some previous studies that showed a link between cannabis, heart rate and blood flow.

Published in the European Journal of Preventive Cardiology, the latest study is based on more than 1,200 people who took a U.S. survey in 2005. The National Health and Nutrition Examination Survey, under the federal Centers for Disease Control and Prevention, is based on a questionnaire and physical examination. Responders answered a range of questions, including about marijuana use.

The authors compared the surveys with 2011 mortality data for the same group of people. They found a higher prevalence of cardiovascular death among those who said they used marijuana in 2005, compared with those who did not.

The study controlled for those who had previously been diagnosed with high blood pressure. But it did not take other cardiovascular risk factors into account, including diet and exercise.

It also assumed that those who said they had used marijuana in 2005 continued to do so, and it assumed that users largely smoked their pot and didn't consume it in other ways, such as by eating marijuana-laced brownies.

Those caveats limit the study's validity, said Dr. Vinay Prasad, associate professor of medicine at Oregon Health & Science University and an expert on the design and results of medical studies.

"It does not prove that if you choose to use marijuana you are more likely to die of cardiovascular disease," Prasad said in an email. "I think the major limit of the study is that there may be unobserved differences between the people who used and admitted to using marijuana during the years of this study, and cardiovascular outcomes that the researchers did not adjust for.  In fact, that is likely."

Some studies have found a link between marijuana and the cardiovascular system. One showed that cannabis increases heart rate. Another review found an association between using marijuana and acute coronary syndrome. Yet another study found no link between heart disease and death.

The authors of the latest study said more research is needed.

"We recommend purposeful designed follow-up studies to assess the relationship between marijuana use and cardiovascular mortality," lead author Barbara Yankey of Georgia State University, said in an email.