New York, Jul 28 (IANS): Inhaling even a minute of secondhand marijuana smoke is likely to cause damage to the blood vessels, a study warns.

The findings showed that the blood vessels of rats who were exposed to only a minute of breathing secondhand marijuana smoke took at least three times longer to recover their functions.

"Arteries of rats and humans are similar in how they respond to secondhand tobacco smoke, so the response of rat arteries to secondhand marijuana smoke is likely to reflect how human arteries might respond," said Matthew Springer, Professor at the University of California, San Francisco.

When rats inhaled secondhand marijuana smoke for one minute, their arteries carried blood less efficiently for at least 90 minutes, whereas similar exposure to secondhand tobacco smoke caused blood vessel impairment that recovered within 30 minutes.

"While the effect is temporary for both cigarette and marijuana smoke, these temporary problems can turn into long-term problems if exposures occur often enough and may increase the chances of developing hardened and clogged arteries," Springer added.

Blood vessel function was examined in rats before and after exposure to secondhand marijuana smoke at levels similar to real-world secondhand tobacco smoke.

Further, the team also found that the mere burning of the plant material is responsible for the impaired blood vessels, not chemicals like nicotine and tetrahydrocannabinol (THC) -- the psychoactive ingredient in marijuana -- or rolling paper.

"There is widespread belief that, unlike tobacco smoke, marijuana smoke is benign," Springer said.

People have often been told to avoid secondhand tobacco smoke for years, but not to avoid secondhand marijuana smoke, because until now there had been no evidence that it can be harmful, said the paper appearing in the Journal of the American Heart Association.

The inhalation of smoke should be avoided, regardless of whether it comes from tobacco, marijuana, or other sources, researchers suggested.