Large-scale study compares impact of cigarette and marijuana smoking
The research team analyzed a large national database to compare the lung function of marijuana and tobacco smokers over an extended period of time. Researchers found that although smoking cigarettes or being exposed secondhand smoke decreases lung volume, smoking marijuana has the opposite effect.
Stefan Kertesz, M.D., a senior author of the study and associate professor in the UAB Division of Preventive Medicine, stated: “Occasional marijuana use was associated with increases in lung air flow rates and increases in lung capacity. Those increases were not large, but they were statistically significant. And the data showed that even up to moderately high-use levels — one joint a day for seven years — there is no evidence of decreased air-flow rates or lung volumes.”
However, Kertesz warned against using marijuana smoke as a means to improved lung health. “It’s not enough of an increase that would make you feel better. Healthy adults can blow out 3 to 4 liters of air in one second. The amount of gain, on average, from marijuana is small, 50 ccs or roughly a fifth of a can of coke. So it’s not something that would be noticeable.” Researchers also pointed out that although most marijuana smoking does not cause long-term lung problems, smokers may still suffer from coughs and minor irritations of the throat and lungs.
The study, which was funded by the National Institutes of Health (NIH), reviewed data acquired by the Coronary Artery Risk Development in Young Adults Study (CARDIA). This long-term research project recruited more than 5,000 subjects, male and female, black and white, from four cities, Chicago, Oakland, Minneapolis and Birmingham. The goal of the project was to study cardiovascular disease development and risk factors. The study analyzed health factors of the participants over the course of twenty years, beginning in 1985 when they were ages 18-30.
Overall, study participants were equally likely to smoke marijuana or cigarettes and some used both. Thirty seven percent of study participants reporting smoking marijuana at some point during the course of the study. Researchers say this compares with percentages in national surveys about US marijuana use.
Tests measured study participants air flow and lung volume at years 0, 2, 5, 10 and 20. Air flow is measured by the amount of air the subject can exhale in a single second after taking a very deep inhalation. Lung volume is measured based on the total amount of air exhaled following a deep inhalation. As the lead author of the study, Dr. Mark Pletcher, associate professor of epidemiology and biostatistics at the University of California, San Francisco, noted “In some ways, marijuana smoking is really a lot like doing a pulmonary function test.”
The differences in how people smoke marijuana and cigarettes may also partly explain the difference in how these habits affect lungs, say the researchers. Cigarette smokers in the study smoked an average of eight cigarettes a day. On the other hand most marijuana smokers, smoked two or three times a month. With heavier marijuana use there was some decrease in lung function. The study did not distinguish between different methods of marijuana inhalation.
THC has protective effect
One expert not involved in the study, Dr. Donald Tashkin, from the University of California, Los Angeles, who has studied marijuana for over 30 years, notes the results of the study may be partially explained by the anti-inflammatory effects of marijuana’s active ingredient. “We don’t know for sure, but a very reasonable possibility is that THC may actually interfere with the development of chronic obstructive pulmonary disease.”
It is ironic that this study was funded by one agency of the federal government, the NIH, at the same time that federal law enforcement is cracking down on medical marijuana dispensaries in many states. Perhaps the Department of Justice should review the findings of the recent study.