Matthew Springer, a researcher in cardiovascular disease, was attending a Paul McCartney concert at AT&T Park in San Francisco in 2010 when he took particular note of the “haze of smoke over the whole audience.”
Springer, a professor of medicine at UC San Francisco, had studied the effects of secondhand tobacco smoke on heart and vascular function. But this smoke was marijuana, a fact that McCartney noted from the stage as the performer commented on the familiar herbal-scented San Francisco air, Springer recalled.
“There were all these people who wouldn’t have tolerated people next to them smoking cigarettes. But it was OK with marijuana,” he said.
Springer, who spoke April 21 at the UC Center in Sacramento, said the concert haze and aroma inspired a research curiosity: What is the impact of secondhand marijuana smoke on blood vessel function?
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His preliminary research, presented in 2014 at the American Heart Association’s Scientific Sessions, suggested that smoke from marijuana can damage your heart and blood vessels as much as secondhand cigarette smoke.
The findings, from studies on rats exposed to marijuana smoke containing both psychoactive tetrahydrocannabinol (THC) and no THC at all, showed that blood vessel function dropped 70 percent after 30 minutes of either type of exposure.
Regardless of whether it comes from cigarettes, pot or other burning substances, Springer concluded, “it is very clear that secondhand smoke is a health hazard.”
In 2006, a UCLA study, headed by research physician Dr. Donald Tashkin, said marijuana smoke contains carcinogens and even has more tar than tobacco smoke. But the findings concluded that long-term marijuana smokers didn’t have an increased risk of developing lung cancer, with Tashkin speculating that THC may reduce cancer rates in aging cells.
A 2013 study led by Tashkin also said that habitual marijuana use alone doesn’t lead to significant abnormalities in lung function.
Nationally, long-term exposure to secondhand cigarette smoke is blamed for 50,000 deaths a year in the United States, including an estimated 34,000 deaths from heart disease. Springer says he isn’t ready to extrapolate such numbers to marijuana, given different exposure patterns.
But he said the lab rat research, to be updated in a future study, suggests that blood vessel function is slower to recover from short-term marijuana exposure than with tobacco. In cases where rats were exposed to tobacco smoke for one minute, Springer said, their blood vessel function took about a half an hour to recover. But with marijuana, vessel function didn’t return by 90 minutes – the maximum time that researchers tested.
Springer said researchers haven’t fully theorized why burning marijuana constituents seemed to have a greater impact than tobacco in “impairing vascular function.” He said more study is needed.
The research didn’t examine vaporizing, a non-combustible consumption method increasingly popular among cannabis consumers. But Springer said the findings illustrate that secondhand marijuana smoke should be considered in a similar public policy realm as secondhand tobacco smoke.
Under California law, it is currently illegal for medical marijuana users to smoke cannabis in any area where tobacco is banned, as well as within 1,000 feet of a school or youth center. A likely 2016 ballot measure to legalize marijuana for recreational use, the Adult Use of Marijuana Act, would prohibit marijuana consumption “in any public space” other than premises authorized by local governments.
Springer says he is taking no position on the measure but hopes it triggers a public health policy discussion on secondhand exposure to marijuana smoke.