A study published in the journal Drug and alcohol addiction explored the association between cannabis use and physical health among 308 pairs of twins. Although cannabis use was associated with reduced physical activity and increased loss of appetite, these associations appeared to be driven by genetic and environmental factors rather than the use of cannabis itself.
Although the physical health effects of tobacco use and alcohol use are well established, less is known about the effects of cannabis use. The results in this area are mixed, although some studies have suggested that cannabis has an impact on respiratory health, cardiovascular health, and body mass index (BMI).
To gain a better understanding of the physical health effects of cannabis use, study author Jessica Megan Ross and her team looked at data from a co-twin control study conducted between monozygotic twins (twins who share the same 100% of their genetic makeup) and dizygotic twins (twins sharing 50% of their genetic makeup). This co-twin design allowed the researchers to check for shared genetic and environmental factors while examining the results of interest.
“Understanding the impact of cannabis use on physical health is a major public health concern because existing literature has reported mixed results,” said Ross, assistant professor at the Anschutz Medical Campus at the University of Colorado. Changes in the legalization of cannabis use in the United States have been associated with the increase in cannabis use in adults. However, we still don’t have a clear picture of how cannabis use affects physical health. “
The data came from an ongoing study called the Colorado Adoption / Twin Study of Lifespan Behavioral Development and Cognitive Aging (CATSLife). This longitudinal study includes a sample of 308 pairs of twins (164 monozygotic twins, 144 dizygotic twins) who were followed from infancy to adulthood.
During adolescence, young adulthood and adulthood, respondents were asked to independently report how often they used cannabis, tobacco, alcohol and other drugs. The researchers calculated the average frequency of cannabis use over the lifetime of each participant by calculating the average number of days in the last month they had used cannabis during the three assessments.
At the adult assessment alone, the health functioning of the participants was measured with various assessments administered by the research staff. Measurements included blood pressure, heart rate, and lung function. Participants also self-reported various health measures such as chronic pain, nausea, breathing difficulties, headaches, and injuries. They also indicated whether they had exercised in the past 24 hours and answered questions about how often they consumed healthy and unhealthy food.
In their analysis, the researchers considered the effects both between families and within the family. Effects between families were measured by averaging the frequency of cannabis within each pair of twins and comparing these averages between pairs of twins. Effects within the family were measured based on a twin’s deviations from the mean cannabis frequency within their pair of twins.
At the intra-family level, greater cannabis use in adolescence was associated with less frequent exercise in adulthood, and greater cannabis use in adulthood was associated with more frequent loss of appetite. However, these effects were not present within the family. This suggests that the effects were driven at least in part by family factors shared within twin pairs and not causally related to cannabis use. For example, the study authors suggest that some people may be genetically predisposed to cannabis use and at the same time predisposed to exercise less and lose their appetite more often.
“We examined whether cannabis frequency is phenotypically associated with physical health outcomes and after controlling for shared genetic and environmental factors through a co-twin longitudinal control design. We also conducted the exact same analyzes with tobacco frequency and physical health to provide a comparison. Overall, the results of this study do not support a causal association between once-weekly cannabis use (the average cannabis frequency of the adult sample) and the detrimental effects on the physical health of individuals aged 25 and older. and 35, “Ross told PsyPost.
At the twin level, more frequent cannabis use in adulthood was associated with a lower resting heart rate, but only among monozygotic twin pairs. This effect remained significant after controlling for family factors and other substance use, presenting some evidence of a causal relationship between cannabis use and resting heart rate.
“Our study included 25 different physical health outcomes such as anthropometry (e.g., body mass index), lung function, cardiovascular function (blood pressure, heart rate), hand grip, chronic pain frequency, and diet,” he said. Ross. “Furthermore, the results for cannabis use contrast markedly with those for tobacco use in the present study, which were consistently associated with poorer physical health.”
The researchers noted several limitations to the study, including the fact that the results may not be generalized to the broader US population. “It is important to keep in mind that these findings only apply to adults (aged 25 to 35) who consume cannabis, on average, once a week. These findings don’t apply to teenagers or adults who use cannabis more frequently, ”Ross said.
The prevalence of obesity in the sample was much lower than the national average, suggesting that participants may have been more health conscious than the average American. Since a lower BMI corresponds to a lower resting heart rate, this may have affected the results.
“It is important to note that we do not suggest that cannabis is safe for everyone to use,” Ross added. “While we have not found that cannabis use (once a week) is associated with harmful effects on physical health, people can still develop other negative outcomes from use such as a cannabis use disorder.”
The study, “The effects of cannabis use on physical health: A co-twin control study”, was written by J. Megan Ross, Jarrod M. Ellingson, Maia J. Frieser, Robin C. Corley, Christian J. Hopfer, Michael C. Stallings, Sally J. Wadsworth, Chandra A. Reynolds and John K. Hewitt.