Smokers who light up an occasional joint may be putting themselves at a dramatically higher risk of developing chronic lung disease, according to a new study by Canadian researchers.
The findings indicate that marijuana, even in small doses, seems to accelerate the harmful effects of smoking and greatly boosts respiratory problems and chronic obstructive pulmonary disease ( COPD ). The disease, which is often caused by smoking, actually encompasses a few disorders, including chronic bronchitis and emphysema. People with COPD often have difficulty breathing and shortness of breath, and experience increased coughing. It's one of the leading causes of death in Canada.
In the study, published today in the Canadian Medical Association Journal, researchers found that, as expected, smokers were at an increased risk of developing COPD. But that risk was much higher among those who smoked cigarettes as well as marijuana, according to Wan Tan of the James Hogg iCapture Centre for Cardiovascular and Pulmonary Research, based at St. Paul's Hospital in Vancouver.
"Smoking marijuana and cigarettes is harmful for your lungs even in small amounts if you smoke them together," said Dr. Tan, who is the study's lead author.
But the risk of developing COPD was not heightened among those study participants who said they smoked only marijuana.
Researchers don't know exactly why smoking tobacco and marijuana apparently boosts the risk of the lung disease so greatly. Dr. Tan said they believe a chemical reaction may occur in the individual's airway that spurs the onset of health problems.
Study participants who reported smoking both tobacco and marijuana were almost three times more likely to develop COPD than non-smokers, as determined by spirometric testing.
In the study, researchers surveyed nearly 900 randomly selected Vancouver residents aged 40 or over.
Researchers defined smokers as anyone who reported having at least 365 cigarettes in their lifetime, while marijuana users were defined as anyone who had smoked the substance in their lives. Researchers defined substantial marijuana use as anyone who reported smoking at least 50 marijuana cigarettes in their life.
They found the risk of developing COPD among cigarette smokers increased if they were heavy marijuana users.
While the risk of COPD didn't seem to noticeably
increase among those who only smoked marijuana, that doesn't mean they're not doing damage to their lungs.
Dr. Tan said the study found the risk of developing COPD was slightly higher among those who smoked only marijuana. The increase was too small, however, for researchers to draw conclusions about health risks.
More research should be done focusing solely on the health risks of smoking marijuana, Dr. Tan said, to address public confusion about the issue.
"It's not really widely known that it has this harmful effect. I think [people] are probably a bit confused by the lack of information in the public domain to tell them that it's actually got a harmful effect."
Despite this, an editorial being published today with the study suggests that marijuana users may not need to worry their habit will lead to serious lung problems. Dr. Tan's study, as well as past research, hasn't identified a strong association between marijuana use and chronic lung disease, writes Donald Tashkin, medical director of the Pulmonary Function Laboratory in the division of pulmonary and critical care medicine at the David Geffen School of Medicine at the University of California, Los Angeles.
Dr. Tashkin argued the scant evidence supporting the link means that "we can be close to concluding that marijuana by itself does not lead to COPD."
Author: Carly Weeks
Pubdate: Tue, 14 Apr 2009
Source: Globe and Mail