Long-term marijuana use was linked to poorer periodontal health in later life, but it was not associated with other physical health problems.
However, the study found no link between long-term use of the drug and greater risk of other physical health problems.
Marijuana - also referred to as cannabis - is the most commonly used illicit drug in the United States.
According to a 2014 survey from the National Institute on Drug Abuse (NIDA), around 22.2 million Americans report using the drug in the past month.
Marijuana use is particularly common among adolescents and young adults. NIDA report that in 2015, almost 35 percent of 12th graders had used marijuana in the past year, while 21.3 percent were current users.
However, the long-term effects of marijuana use on physical health are less clear, and this is something the researchers of this latest study set out to address.
Periodontal health at risk with persistent marijuana use
Study co-author Madeline H. Meier, Ph.D., of Arizona State University, and colleagues analyzed the data of 1,037 adults who were part of the Dunedin Multidisciplinary Health and Development Study of New Zealand.
Subjects were born in New Zealand in 1972-1973 and were followed up from birth until the age of 38 years. Participants underwent regular health and lifestyle assessments during follow-up.
- Around 47.2 percent of American adults aged 30 and older have some form of periodontal disease
- The condition is more common among men than women
- Poor oral hygiene, smoking, and diabetes are known causes of periodontal disease.
Meier and colleagues looked at the frequency of marijuana use among participants between the ages of 18-38 and assessed whether this impacted physical health at the age of 38.
Specifically, they looked at whether marijuana use affected later-life periodontal health, lung function, systemic inflammation, and metabolic health.
Compared with participants who did not use marijuana, the researchers found persistent marijuana use for up to 20 years was associated with greater risk of periodontal disease at the age of 38.
Periodontal disease arises as a result of infection and inflammation of the gums and bone surrounding the teeth.
It presents as gingivitis in its early stages, characterized by red, swollen, and bleeding gums. As it becomes more serious, it can lead to periodontitis, where the bone around the teeth is lost. This can cause the teeth to fall out.
The researchers note that previous studies have indicated that marijuana users tend to brush their teeth and floss less frequently than non-users, and they are also more likely to have alcohol dependence - all factors that can contribute to periodontal disease.
When it came to other later-life physical health problems, however, long-term marijuana users were found to be at no greater risk than non-users of the drug.
Commenting on their results, the authors say:
"In general, our findings showed that cannabis use over 20 years was unrelated to health problems in early midlife.
Across several domains of health (periodontal health, lung function, systemic inflammation, and metabolic health), clear evidence of an adverse association with cannabis use was apparent for only one domain, namely, periodontal health."
They add that the results should be "interpreted in the context of prior research" that shows marijuana use may raise the risk of accidents and injuries, bronchitis, cardiovascular problems, infectious diseases, cancer, and poor mental health.
The team points to a number of study limitations. For example, marijuana use was self-reported, and some participants may have been reluctant to disclose their use of an illegal drug.
Additionally, the study only looked at the effect of marijuana use on specific health problems.