Middle-aged and older women with gum disease are slightly more likely than those without gum problems to develop breast cancer, suggests a new study.
The risk increase was most pronounced for women with gum disease who smoked cigarettes or had quit within the past 20 years, although the authors caution that the reasons for the links are still not known.
"We don't know if it's causal, we need to keep that in mind," said lead author Jo Freudenheim, distinguished professor in the Department of Epidemiology and Environmental Health in the University at Buffalo's School of Public Health and Health Professions in New York State.
It could be that these characteristics are correlated with something else that's causing both gum disease and breast cancer, she told Reuters Health.
The researchers analyzed data on more than 73,000 postmenopausal women enrolled in the Women's Health Initiative Observational Study who did not have breast cancer to start with.
About one quarter said they had periodontal disease, a chronic inflammation and infection of the gum tissue around the base of teeth. Gum disease has also been tied to heart disease, stroke, diabetes and some other cancers.
After an average of about six and a half years of follow-up, about 2,100 women had been diagnosed with breast cancer. The risk of breast cancer was 14 percent higher for those with gum disease compared to those without it, according to the results in Cancer Epidemiology, Biomarkers and Prevention.
When researchers adjusted for a variety of other breast cancer risk factors, including age, weight, exercise, alcohol use and smoking, the extra breast cancer risk associated with gum disease fell to 11 percent.
Researchers then looked at women with breast cancer grouped by smoking status, and found that 23 percent of never smokers had gum disease, 34 percent of former smokers had gum disease and 47 percent of current smokers had gum disease.
In this analysis, never smokers with gum disease had a very small 6 percent increased risk of breast cancer compared to those without gum disease, and for former smokers who had quit more than 20 years earlier there was a similarly small risk increase. For more recent quitters, however, the added risk was 36 percent higher and for current smokers, it was 32 percent higher.
"It could be that periodontal disease means there's kind of a general inflammation in the body," Freudenheim said. "Inflammation is related to a number of cancers and stroke and heart disease, so it could be that chronic inflammation is causing both."
"Another possible mechanism could be that bacteria from the periodontal lesions could enter the blood stream and lead to changes in the tissues which are distant from the mouth," said Gerard Linden, professor of periodontology at the Center for Public Health at Queen's University Belfast in Northern Ireland.
"There are changes in sex hormone levels related to the menopause that may affect the response of breast tissues to a stimulus such as exposure to bacteria," said Linden, who was not part of the new study, by email.
Postmenopausal women should be sure to have regular dental checkups, he said.
"We're just starting now to understand how important what we call the microbiome is to general health," and the mouth and gut are full of important microbes, Freudenheim said.
Smoking is strongly tied to gum disease, and less strongly linked to breast cancer, she said.
It's too early to say that treating or preventing gum disease lowers breast cancer risk, she said.
But, "if what people do in response to this is take care of their teeth that can't be a bad thing," she said.