There doesn't seem to be any shortage of reasons cited as to why marijuana is bad for health. Now from the world of dentistry comes another: regular pot-smoking seems to bump up the risk of developing gum disease — and earlier in life than expected.

In a study of more than 900 young adults, researchers found that heavy tokers were 1.6 times more likely to have at least mild periodontal disease, compared to those who had never smoked grass.

Heavy users were defined as those who indulged an average of 40 times per year between the ages of 18 and 32, the equivalent of almost once a week.

As a group, their risk of having at least one site with more severe gum disease was triple that of the group who never used the illicit drug, say the researchers, whose work is published in Wednesday's issue of the Journal of the American Medical Association.

What's more, regular pot smokers developed periodontal disease — a chronic bacterial infection that can lead to tooth loss — at a younger age than is normally seen in the general population.

In North America, "we think about periodontal disease as being a problem after the age of 35," said  co-author James Beck, a professor of dental ecology at the University of North Carolina at Chapel Hill.

"These findings, that almost 30 per cent of individuals at age 32 had periodontal disease, indicate that this younger group may need more attention," Beck said.

The apparent effects of cannabis were independent of other gum disease risk factors, including tobacco use, socioeconomic status and infrequent trips to the dentist, the researchers found.

Tobacco products linked to gum disease

Dr. Darryl Smith, president of the Canadian Dental Association, said tobacco use has long been known to increase a person's risk of getting gum disease, and "there are similarities between cannabis, or marijuana and use of tobacco."

"I see the effects of periodontal disease daily in my practice, and certainly a very high percentage of those people are (tobacco) smokers," Smith said from his dental office in Valleyview, Alta., a small, rural community northwest of Edmonton.

Chemicals in cigarette smoke and in other forms of tobacco are believed to reduce blood flow in tissues around the teeth and also to dampen down the immune system's ability to keep oral bacteria in check, leading to chronic gum inflammation.

"It would seem very likely that there could be a similar effect with marijuana, and certainly we know that marijuana contains a lot of potential toxins," he said.

In fact, the researchers say, cannabis contains more than 400 chemical compounds, many of them similar to those found in tobacco.

Their study involved 903 participants born in Dunedin, N.Z., between 1972 and 1973, who provided details of the previous year's cannabis use when aged 18, 21, 26 and 32. They were also given dental exams at age 26 and 32.

Researchers found that the prevalence of regular cannabis use more than doubled from age 18 to 26 and then fell slightly by age 32. As well, pot smokers were more likely to be male, to have lower socioeconomic status and were less likely to make dental visits.

Plaque levels at age 32 were significantly higher among frequent weed users than among those who never smoked pot or had only used it occasionally.