Study links marijuana smoking to gum disease

WASHINGTON (Reuters) - Smoking marijuana, much like smoking tobacco, may increase a person's risk for gum disease that can lead to tooth loss, researchers said on Tuesday.

A study of 903 New Zealanders found that people who smoked marijuana frequently had triple the risk for severe gum disease and a 60 percent higher risk for a milder form of it compared to people who did not smoke the drug, also called cannabis.

People who smoked marijuana less frequently had a smaller increased risk for gum disease, the researchers said.

Gum or periodontal disease is an infection of the tissues surrounding and supporting the teeth. In advanced stages, the gums and bone that support the teeth can become seriously damaged and the teeth can become loose, fall out or have to be removed.

"While it has been known for a few years that tobacco smoking is bad for the periodontal (gum) tissues, no one has investigated whether any other type of smoking is also a risk factor," W. Murray Thomson, a professor of dental public health at the University of Otago in New Zealand, said by e-mail.

"We suspected we would indeed find that cannabis smoking was a risk factor, but what surprised us was the strength of the relationship," added Thomson, who led the study published in the Journal of the American Medical Association.

His team tracked a group of people in Dunedin, New Zealand, since their births in 1972 and 1973. They were age 32 when the researchers identified the "strong association" between marijuana use and gum disease.

The researchers defined heavy marijuana users as those who reported smoking it an average of 41 or more times annually between ages 18 and 32 -- almost once a week.

Many heavy marijuana users also were tobacco smokers, but the researchers said their statistical analysis showed that marijuana increased the risk for gum disease separate and apart from tobacco use.

"Cannabis smoking appears to have an effect which is not far behind that of tobacco," Thomson said.

Thomson said the study adds to the understanding of health consequences from smoking marijuana. "We already knew that it had respiratory and mental health effects on some people, but this is a totally new angle on its effects," Thomson added.

Researchers think tobacco smoking can lead to periodontal disease by interfering with immune function, inflammatory response and blood flow in the gums. Thomson said he thinks marijuana smoking may act in a similar way.

James Beck of the University of North Carolina School of Dentistry, who also worked on the study, said he hopes further research is conducted to confirm a link between marijuana and gum disease.

A U.S. group supporting legal sales and regulation of marijuana faulted the study. "I think they've raised an interesting question, but I don't think they're close to giving a meaningful answer," Marijuana Policy Project spokesman Bruce Mirken said.

Mirken called the study's definition of heavy marijuana use arbitrary and said additional factors like alcohol or other drug use may help account for the findings.

(Editing by Maggie Fox and Cynthia Osterman)