Although some studies suggest that regular marijuana use lowers levels of fasting insulin and glucose as well as decreases the odds of developing diabetes, a new study published in Diabetologia shows that current and former marijuana users are more likely to have prediabetes than those who have never used the drug.1
Marijuana is the most commonly used illicit drug in the United States, according to the National Institutes of Health (NIH).2 The drug is sold recreationally in a growing number of states, including Colorado, Washington, Oregon and Alaska, and is prescribed increasingly throughout the United States for medical use.
Some marijuana plants are bred to have very little or very high THC content. More and more people are consuming customized strains of the plant in food, tinctures and beverages. Currently, it is unknown how smoking vs. eating marijuana may vary in terms of health effects and glucose metabolism.
Researchers at the University of Minnesota School of Public Health investigated the association between self-reported marijuana use and concurrent and incident prediabetes and full blown type 2 diabetes. They analyzed both the quantity of marijuana used and status of current use.
The researchers also examined the role of BMI and waist circumference as potential confounding and/or mediating factors to these associations. In addition, they factored in gender and race risk profiles and looked at the effects of gender and race on the associations.
“Results from the cross-sectional studies with larger study populations have suggested marijuana use to be associated with improved metabolism, including lower levels of fasting insulin and glucose and lower odds of diabetes. However, we felt the uncertainty surrounding the timeline of marijuana use and disease development was a limitation of previous research, and possibly induced bias in the previous results,” said lead study investigator Mike Bancks, MPH, who is the National Heart, Lung, and Blood Institute (NHLBI) Cardiovascular Disease Epidemiology and Prevention pre-doctoral fellow at the University of Minnesota School of Public Health in Minneapolis.
What has been lacking until now is an assessment of marijuana use prior to the development of prediabetes and diabetes, according to Bancks. Therefore, he and colleagues sought to fill this gap in knowledge.
Evidence Linking Marijuana Use to Prediabetes
The researchers analyzed data from the community-based Coronary Artery Risk Development in Young Adults (CARDIA) study to determine marijuana use and the presence of prediabetes and diabetes.
At study recruitment, which took place from 1985 to 1986, participants ranged in age from 18 to 30 years. Currently, they are in their 30th year of observation.
The association between marijuana use and prevalence of prediabetes and diabetes was examined in 3,034 participants at CARDIA exam year 25 (2010-2011).
The researchers also assessed the incidence of prediabetes and diabetes according to previous marijuana use in 3,151 individuals who did not have prediabetes or diabetes at year 7 (1992-1993).
In this study, the percentage of individuals who self-reported current use of marijuana declined during follow-up (28% in 1985-1986 to 12% in 2010-2011).
After adjustment for behavioral/lifestyle and physiological characteristics, the researchers noted a 65% increase in the odds of currently having prediabetes in individuals who reported current use of marijuana compared with individuals who reported never using marijuana.
After 18 years of follow-up, results revealed a 40% greater risk for developing prediabetes — but not diabetes — for individuals who reported a lifetime marijuana use of at least 100 times compared with individuals who reported never using the drug.
BMI and waist circumference did not affect the associations, according to the data.
“Because little is known about marijuana use and metabolic health and because our results do not align with what has been previously investigated, this may surprise the public. More importantly, it strongly suggests more research is needed on the health effects of marijuana use,” Bancks told Endocrinology Advisor.
Interestingly, the study failed to establish a direct link between marijuana use and type 2 diabetes. The researchers stated that it is unclear how marijuana use could place an individual at increased risk for prediabetes yet not diabetes.
“The mechanisms by which marijuana (cannabis) may affect metabolism are not entirely clear. The two main active components of marijuana, delta-9 –tetrahydrocannabinol (THC) and cannabidiol, bind to cannabinoid receptors in the body, which are expressed in multiple regions of the brain and tissues in the body. In the brain, these receptors influence eating and appetite, and in the abdominal and peripheral tissues of the body, these receptors can influence fat accumulation and lipid metabolism,” said Bancks.
He said the blocking and activating of these receptors may vary by specific tissues, with differential physiological results. As a follow-up to this project, he and his team are looking at the association between marijuana use and accumulation of abdominal adipose tissue and liver attenuation.
Shichun Bao, MD, PhD, who is an assistant professor of medicine in the division of endocrinology at Vanderbilt University in Nashville, Tennessee, said this study must be viewed with a great deal of caution.
“It does not make too much sense that marijuana use could place individuals at increased risk for prediabetes but not diabetes, as we all know prediabetes is a risk factor for diabetes. [Researchers] should do a prospective randomized trial to study this, and need to give a possible good explanation on the reason why this discordance happened,” Bao told Endocrinology Advisor.
In a study published in 2013, researchers looked at 4,657 adult men and women from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2010. They calculated fasting insulin and glucose via blood samples after a 9-hour fast, and with the homeostasis model assessment of insulin resistance (HOMA-IR).
Using multivariable adjusted models, they found that current marijuana use was associated with 16% lower fasting insulin levels and 17% lower HOMA-IR.3
The study also found significant associations between marijuana use and smaller waist circumferences.
Laura Young, MD, PhD, who is an assistant professor of medicine in the division of endocrinology at the University of North Carolina School of Medicine in Chapel Hill, said marijuana use is common, and in some states a legal part of some patients’ medical regimens.
It is important for health care providers to address all aspects of patients’ health, including drug and alcohol use, she noted.
“It would be surprising to find that marijuana has no effect on glucose metabolism. Therefore, as use increases, it makes sense to delve more deeply into understanding how marijuana affects glucose metabolism. However, it is difficult to rationalize how use of marijuana increases the risk of prediabetes but not overt diabetes as the authors show in this paper,” Young told Endocrinology Advisor.
“Further complicating the issue is that these findings contradict previous research in the field. Additional investigation is certainly necessary to understand the importance of marijuana use and its impact on glucose metabolism.”
- Bancks MP, Pletcher MJ, Kertesz SG et al. Diabetologia. 2015;doi:10.1007/s00125-015-3740-3.
- Drug Facts: Marijuana. National Institute on Drug Abuse website. http://www.drugabuse.gov/publications/drugfacts/marijuana. Updated June 2015. Accessed August 2015.
- Penner EA, Buettner H, Mittleman MA. Am J Med. 2013;126(7):583-589.