Durham, N.C. — Heavy marijuana use has been found to contribute to gum disease, apart from the known effects that tobacco smoke was already known to have.

In a group of more than 900 New Zealanders, smoking cannabis more than 40 times a year since age 18 was found to be responsible for more than one-third of the new cases of periodontal disease between ages 26 and 32, according to a study published Feb. 6 in the Journal of the American Medical Association.

“Heavy cannabis use has been linked to greater risks of developing respiratory disease and some psychiatric conditions,” said Terrie Moffit, a Duke University professor of psychology and neuroscience who participated in the study. “Gum disease should be added to that list of known hazards.”

The study was led by W. Murray Thomson of the school of dentistry at the University of Otago, New Zealand, who measured gum recession at three sites on each tooth at ages 26 and again at 32. The study subjects are part of a longitudinal health and development study that has been tracking nearly 1,000 people born in Dunedin, New Zealand, in 1972 and 1973.

The link between gum disease and marijuana use emerged from a statistical analysis that controlled for gender, dental care, socio-economic status and how clean or dirty the teeth were. Most of the self-identified heavy marijuana users also were tobacco-users, but that factor was controlled statistically. The researchers also were able to focus on study participants who were not tobacco-users, and they still found a link between marijuana use and gum disease.

The precise physiology of smoke’s effect on the gums is still not understood, but the team believes it interferes with immune function, inflammatory response and peripheral blood flow in the gums.