Tooth Loss Linked To Increased Stroke Risk

Ischemic strokes result from a blockage in an artery leading to the brain. They are the most common type of stroke.

In the study, men who had fewer than 25 teeth when they entered the study had a 57 percent higher risk of ischemic stroke than those with 25 or more teeth.

The link between ischemic stroke and periodontal disease, which is caused by bacterial infections, adds another piece to the growing body of evidence that infection plays a role in stroke and heart disease. However, the new study presents a surprising finding about tooth loss.

"The association of ischemic stroke with tooth loss persisted even after we controlled for periodontal disease history, which could reflect severe periodontal disease in the extracted teeth," says Kaumudi J. Joshipura, BDS, Sc.D., an associate professor of epidemiology at Harvard School of Dental Medicine and Harvard School of Public Health in Boston.

Another unexpected – and unexplained – finding was that the association between tooth loss and stroke risk was higher among nonsmokers than among smokers. Smoking tobacco is a risk factor for both ischemic stroke and periodontal disease.

"We don't know why nonsmokers showed a higher association," Joshipura says. "But that lends support to the argument that the association between tooth loss and stroke is not all due to smoking."

The researchers also found that the risk of stroke was mainly related to the number of missing teeth at entry into the study, rather than teeth lost recently during the follow-up phase. This is possibly because only a few teeth were lost during follow-up or may imply that tooth loss takes many years to impact ischemic stroke risk, she says. This study is the first to examine the timing of tooth loss and the effect on stroke risk.

Periodontal disease, tooth loss and ischemic stroke share about a dozen risk factors, including age, smoking, diabetes, and some socioeconomic factors such as low income, Joshipura says.

Researchers studied 41,380 men in the Health Professionals' Follow-Up Study – mostly white dentists, veterinarians, pharmacists, optometrists, osteopathic physicians and podiatrists who were ages 40 to 75 at the start of the 12-year study. The men completed questionnaires mailed to them every two years about their medical history, health behaviors, and the occurrence of cardiovascular problems or other adverse health events.

Participants with fewer teeth were generally older, drank more alcohol, were less physically active and were more likely to smoke.

Researchers documented 349 ischemic strokes in the entire group. Compared to men with 25 to 32 teeth, those with 17 to 24 teeth had a 50 percent higher risk of stroke. Men with 11 to 16 teeth had a 74 percent higher risk and men with 10 or fewer teeth had a 66 percent higher risk of stroke compared to men with the most teeth.

Researchers studied whether the association between tooth loss and ischemic stroke could partly be the differences in diet, such as the amount of fruits and vegetables consumed. "When people loose teeth, they may eat fewer fruits and vegetables," Joshipura says. "And that, in turn, might affect their stroke risk. However, the results suggested that dietary factors evaluated did not seem to play an important role in the association between tooth loss and stroke found in this study."

She also suggested it is too early for physicians to try to apply the study's findings to patients. "I would be a little cautious," Joshipura says. "We need more studies before we can say that this is a causal association."

Six earlier studies had examined the association between stroke and periodontal disease and/or tooth loss but produced conflicting results. The Harvard researchers sought to resolve the relationship, in part by using a more uniform study population with more participants and by collecting data about whether the tooth loss and periodontal disease occurred before the stroke.

The challenge in determining cause and effect is to rule out the risk factors shared by periodontal disease, tooth loss, and ischemic stroke as alternative explanations.

"What is unique about this study is that we looked at a group of health professionals, who by nature are homogenous with respect to education, socioeconomic status and health behavior," she says. "They would be doing more things to keep themselves healthy, whether it is for their overall health, dental health or their cardiovascular health. So if we find an association in this kind of population, it is more likely that it is causal."

Co-authors are Hsin-Chia Hung, Dr.P.H.; Eric B. Rimm, Sc.D.; Walter C. Willett, M.D.; and Alberto Ascherio, M.D.

The study was funded by the National Institutes of Health.