Long-term use of cannabis is associated with a significant increase in the risk of developing gum disease but does not appear to be linked to adverse outcomes on other measures of heath, new data suggest.
Madeline H. Meier, PhD, Department of Psychology, Arizona State University, Tempe, and colleagues found that regular use of cannabis during adulthood was associated with periodontal disease at age 38 years.
However, unlike long-term tobacco use, cannabis was not linked to significant or relevant changes in measures of lung function, systemic inflammation, cardiovascular function, and metabolic health.
Dr Meier told Medscape Medical News she was "somewhat surprised to see that cannabis use was not associated with reduced lung function." Acknowledging that cannabis is commonly smoked with tobacco, she said that "disentangling cannabis and tobacco use is challenging.
"In New Zealand, cannabis is not typically mixed with tobacco, but most participants who used cannabis also smoked cigarettes. Although we controlled for tobacco use, imperfect control might bias the results toward finding spurious associations between cannabis use and poor health. We note, however, that all poor health outcomes, apart from periodontal disease, were unrelated to cannabis use," she added.
The research was published online June 1 in JAMA Psychiatry.
The team examined data from the longitudinal Dunedin Multidisciplinary Health and Development Study of New Zealand, which initially recruited a representative birth cohort of 1037 individuals born in 1972-1973 in Dunedin, New Zealand.
The current analysis was based on 947 study participants for whom complete laboratory data were available and who were alive at age38 years. In all, 46 participants were lost to follow-up, and 30 were deceased.
One tobacco pack-year was defined as the equivalent of smoking 20 cigarettes a day for 1 year; one cannabis joint-year was defined as the equivalent of daily cannabis use for 1 year. Data on tobacco pack-years were missing for two participants, and cannabis joint-year data were missing for seven individuals.
The team reports that 484 of 945 participants (51.2%) had ever used tobacco daily, and 680 of 945 (72.0%) had ever used cannabis daily. Furthermore, 176 of 680 (25.9%) ever daily cannabis users had been diagnosed at least once with persistent cannabis dependence.
Physical examinations and blood samples were used to determine periodontal health, lung function, systemic inflammation, metabolic syndrome, waist circumference, high-density lipoprotein cholesterol (HDL) levels, triglyceride levels, systolic and diastolic blood pressure, glycated hemoglobin levels, body mass index, and self-reported health.
The researchers found that tobacco pack-years were associated with significantly worse health in terms of periodontal health, lung function, systemic inflammation, metabolic syndrome, HDL and triglyceride levels, glycated hemoglobin levels, and self-reported health.
These findings held after taking into account cannabis joint-years, childhood health, and socioeconomic status and when restricting the analysis to tobacco pack-years between the ages of 26 and 38 years.
Cannabis joint-years were associated with worse health in terms of periodontal health, lung function, and self-reported health, but the relationships with periodontal disease and lung function only remained significant after taking into account tobacco pack-years, childhood health, and socioeconomic status.
Specifically, cannabis joint-years were associated with periodontal health at a beta value, representing the increase in risk per standard deviation, of 0.12 (P < .001). The relationship with periodontal disease held even after controlling for brushing and flossing of teeth and for alcohol dependence.
Further analysis indicated that cannabis joint-years from ages 26 to 38 were significantly associated with poorer periodontal health at age 38 years, even after taking into account periodontal health at age 26 years and tobacco pack-years, at a beta value of 0.10 (P < .001).
For lung function, the researchers believe that the association is not likely to be indicative of airway obstruction, because there was no relationship with the forced expiratory volume in the first second.
According to the investigators, the study has "a number of implications" ― primarily that aside from periodontal disease, cannabis is not associated with physical health problems in early midlife. Furthermore, they note that cannabis use is not linked to metabolic effects.
"Our results should be interpreted in the context of prior research showing that cannabis use is associated with accidents and injuries, bronchitis, acute cardiovascular events, and, possibly, infectious diseases and cancer, as well as poor psychosocial and mental health outcomes," the researchers write.
Mental Health Outcomes Not Measured
Richard Saitz, MD, MPH, chair and professor, Department of Community Health Sciences, Boston University School of Public Health, Massachusetts, who was not involved with the study, noted that the investigation had several strengths.
However, he also pointed to several limitations, the most important being in terms of the kinds of health effects that were being examined.
"They didn't measure whether something hurt, they didn't measure whether you died, they didn't measure whether you were in the hospital, they didn't measure whether you developed a clearly defined illness of some sort. They measured tests," Dr Saitz told Medscape Medical News.
"So I think the big point about this study is that they are really measuring surrogate markers for things that people care about, so they're one step removed."
"Is it worthless? No, it's not worthless. It's reassuring to know that some of these biological markers that have been associated with diseases that we do care about don't seem to be affected substantially, so that is nice for now. It is also nice that they measured a range of these, so it wasn't just one, but that does create some statistical issues."
Another aspect of the study that Dr Saitz highlighted is that it is not possible to examine health outcomes in a sample of this size and of this age range. "I guess I'd be thinking about, How do I expect marijuana or cannabis to affect young people?'
"The answer is, I'm not expecting young people to die of heart attacks and cancer and too many other chronic diseases from marijuana use. I'm expecting them to have mental health consequences, which were not measured here. I'm expecting them to have accidents and injuries from being intoxicated, which were not measured here, and I'm expecting them to suffer in some proportion...from the disease of dependence, which is a serious illness."
Dr Saitz highlighted that one of the issues with interpreting the data is that the overlapping proportions of cannabis and tobacco users in the current analysis are unknown.
"We do tend to have this wish and belief that we can isolate factors in studies that are not experiments, like this one, where people choose their behaviors. We think we can identify one risk factor, and the way that we come to that belief is by using sophisticated epidemiological methods.
"We study prospectively, and we use statistical techniques to adjust for things, and that's all great, but in the real world...the fact of the matter is that any one risk factor or any one behavior is usually done in the context of many others, and the clear one that overlaps here is tobacco. So I would definitely worry about their ability to isolate just the effects of cannabis," he said.
Dr Saitz also said that it is "a little odd" that 72% of the cohort were daily users of marijuana at some point, which "seemed high to me." Noting also that the characteristics of the population are not clearly listed in the article, he added: "It just raises questions. Is this really representative?"
This research was funded by grants from the US National Institute on Aging, by a grant from the United Kingdom Medical Research Council, and by a grant from the Economic and Social Research Council. Additional support was provided by the Jacobs Foundation. The authors have disclosed no relevant financial relationships.
JAMA Psychiatry. Published online June 1, 2016. Abstract
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Cite this: Midlife Health Effects of Cannabis Use Limited to Gum Disease? - Medscape - Jun 08, 2016.