New research shows that current and former users of marijuana are more likely to have prediabetes later in life than those who have never used the drug.

Researchers led by Mike Bancks of the University of Minnesota School of Public Health found that marijuana users were 65 percent more likely to have poor blood sugar control in middle age. However, researchers failed to establish a direct link between marijuana use and type 2 diabetes.

"It is unclear how marijuana use could place an individual at increased risk for prediabetes yet not diabetes," researchers said in the study.

Despite the growing movement to legalize marijuana, little is known about its effect on metabolic health. Previous studies on this subject have revealed conflicting results, with some suggesting marijuana can reduce the risk of diabetes, despite others showing that the drug is associated with an increased calorie consumption.

Using data from the community-based Coronary Artery Risk Development in Young Adults (CARDIA), researchers examined the relationship between marijuana use and presence of prediabetes and diabetes. Individuals in the CARDIA study were between the ages 18 and 35 at study recruitment in 1985-1986 and are currently 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) and incidence of prediabetes and diabetes according to previous marijuana use was assessed in 3,151 individuals free from prediabetes and diabetes at Year 7 (1992-1993) who returned for at least one of the four subsequent follow-up examinations over the next 18 years.

"In conclusion, marijuana use, by status or lifetime frequency, was not associated with incidence or presence of diabetes after adjustment for potential confounding factors," researchers said in their study. "However, marijuana use was associated with the development and prevalence of prediabetes after adjustment. Specifically, occurrence of prediabetes in middle adulthood was significantly elevated for individuals who reported using marijuana in excess of 100 times by young adulthood."

Researchers said their findings, which are detailed in the journal Diabetologia, contrast with those previously reported on marijuana use and metabolic health.

"Future studies should look to objectively measure mode and quantity of marijuana use in relation to prospective metabolic health," researchers said.