Researchers, led by Jo L. Freudenheim from the University at Buffalo's School of Public Health and Health Professions, found that postmenopausal women with gum disease are at increased risk for breast cancer.
The study followed 73,737 postmenopausal women who were part of the Women's Health Initiative Observational Study for 6.7 years. None of the women had breast cancer at the start of the study, but 26.1 percent of them had periodontal disease.
The researchers took into account the women's smoking habits, if any, because previous studies have shown that smoking affects gum disease.
At the end of the study, 2,124 women were diagnosed with breast cancer. Among these, those who had gum disease showed a 14 percent higher risk for breast cancer.
Additionally, among women who had gum disease, those who had quit smoking within the past 20 years were 36 percent more likely to develop breast cancer. On the other hand, those who had quit smoking for more than 20 years had a six percent risk for breast cancer. Those who never smoked at all but had periodontal disease had an eight percent risk for breast cancer.
Based on these results, the researchers explained that smoking possibly affected cancer development, and its effects could not be reversed quickly.
"We know that the bacteria in the mouths of current and former smokers who quit recently are different from those in the mouths of nonsmokers," Freudenheim noted in a press release.
The researchers offered a couple of explanations for the link between gum disease and breast cancer, saying the breast tissues could have been affected by a systemic inflammation caused by gum disease or by mouth bacteria that have entered the circulatory system. However, no cause-and-effect association was established.
"If we can study periodontal disease and breast cancer in other populations, and if we can do more detailed study of the characteristics of the periodontal disease, it would help us understand if there is a relationship," Freudenheim said. "There is still much to understand about the role, if any, of oral bacteria and breast cancer."
The study was published online Dec. 21 in the journal Cancer Epidemiology, Biomarkers and Prevention.
