Chances of serious lung disease about three times more likely than in non-smokers, study says
People who habitually smoke both tobacco and marijuana are about three times more likely than non-smokers to develop serious lung disease.
That affects a lot of people because nearly 20 per cent of Vancouverites over the age of 40 do or have done just that, according to a new study by a team from St. Paul's Hospital.
People who smoked only cigarettes were 2.7 times more likely than non-smokers to have chronic obstructive lung disease. Those who smoke or smoked both cigarettes and marijuana were 2.9 times more likely to have the disease.
The study, published today in the Canadian Medical Association Journal, included nearly 900 Vancouver residents recruited into the study by random telephone dialing.
It showed that 14 per cent of participants now smoke only pot and 14 per cent smoke tobacco. Only 38 of the 856 participants now smoke both marijuana and tobacco. But 160 participants (18 per cent) were either current or previous users of both.
Consistent with previous population surveys showing B.C. has the highest marijuana use in the country, 45.5 per cent of participants in the current study said they had used marijuana in the past.
The study was designed to estimate the prevalence of chronic obstructive lung disease (COPD) among adults over the age of 40 in the general population and the associations with smoking.
Researchers from iCapture Centre for Cardiovascular and Pulmonary Research, a department at St. Paul's, had expected 15 per cent would have lung disease, but the study found it was 19.3 per cent.
About half of the people with clinical signs of lung disease had not yet been diagnosed with it -- they found out when they did lung function tests for the purposes of the study.
Lead author and respirologist Dr. Wan C. Tan said those study participants were given the results of their tests so they could share them with their family doctors, get referred for specialist care or, ideally, "take smoking cessation more seriously."
COPD -- which includes chronic emphysema or chronic bronchitis -- is often indicated by a continuing cough with phlegm and wheezing or shortness of breath. Tan said COPD is a progressive disease and is the fourth leading killer in North America, behind cancer, heart disease and stroke.
In the study, researchers found that participants with COPD had a greater likelihood of other illnesses like asthma, heart disease and high blood pressure. They were more likely to have a history of hospital admission for respiratory problems.
Marijuana smoking alone did not appear to cause COPD.
Although marijuana-only users had a 1.6 times greater risk of COPD than non-smokers, Tan said researchers are not convinced of the statistical power of that odds ratio because there were too few study participants who used marijuana alone in the COPD group.
Experts have found one marijuana joint is equal to the effects (on lungs) of 2.5 to five cigarettes. But while there is well-established evidence of lung damage from cigarettes, research has shown conflicting results on marijuana use.
The current study does not appear to provide clear answers, except for users of either tobacco alone or users of both marijuana and tobacco.
Since the study will now be repeated in other Canadian cities, the larger data set should reveal a more convincing picture of marijuana's role in the development of lung disease, Tan said.
"Innately, it seems logical that marijuana would be a risk factor for COPD. The noxious fumes are identical except for the THC in marijuana and the nicotine in tobacco," said Tan, adding there is a synergistic effect between marijuana and tobacco smoking. Marijuana may sensitize the lungs and exacerbate the effects of tobacco on the airways.
Study authors said the findings should have implications for public policy and additional research. "Anti-smoking campaigns should include a reduction in marijuana use among their goals, aiming especially at those who regularly use both marijuana and tobacco," states the paper's conclusion.
The local research was funded through a $200,000 grant from pharmaceutical companies AstraZeneca, Boehringer-Ingelheim, GlaxoSmithKline and Pfizer Canada. Tan said the companies provided an unrestricted grant and had no role in the study design, data collection, analysis, interpretation or writing.
Sun Health Issues Reporter
pfayerman@vancouversun.com
See more health news at vancouversun.com/health
Risk of chronic obstructive pulmonary disease among current and former marijuana smokers
COPD defined by lung function testing, patient reports of symptoms or physician's diagnosis of chronic bronchitis or emphysema
Group Number Adjusted (n/N) odds ratio
COPD defined by spirometric testing
Tobacco* and marijuana** 25/160 2.90
Tobacco only* 79/286 2.74
Marijuana only** 4/54 1.66
Non-smokers 35/364 1.00
COPD defined by self-report
Tobacco* and marijuana** 98/160 2.39
Tobacco only* 174/286 1.50
Marijuana only** 14/54 0.62
Non-smokers 163/364 1.00
COPD defined by self-report of physician diagnosis
Tobacco* and marijuana** 13/160 1.53
Tobacco only* 32/286 2.07
Marijuana only** 1/54 0.67
Non-smokers 18/364 1.00
n= number with condition, N= number in category
*Participants who had smoked at least 365 tobacco cigarettes.
**Participants who had smoked at least 50 marijuana cigarettes.
Can. Medical Association Journal
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