People, keep brushing your teeth. Breast cancer in post-menopausal women has now joined the growing list of conditions made significantly more likely by gum disease.
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Unsurprisingly, a smoking habit – even in the past - makes the numbers much worse. Even among women who had quit tobacco within the past 20 years, those with periodontitis had a 36 percent higher risk of breast cancer.
Periodontitis is chronic bacterial infection of the hard and soft tissue supporting the teeth. It had previously been associated with increasing the probability of head and oral cancers, kidney and pancreatic cancer, cancers of the blood, lung conditions (such as pneumonia), diabetes, stroke, heart trouble and even bone loss in the jaw.
Gum disease is so common as to be practically a cliché. The women who participated in this enormous study seem to have been blessed: only a quarter had gum disease, compared with nearly half (47%) of adult Americans aged 30 and more, according to a survey by the U.S. Centers for Disease Control and Prevention (for 2010). That's about 65 million people, of which 8% had serious periodontitis. There's no reason to assume that the condition's rates have diminished since then.
The correlations found between periodontal disease and serious illnesses were what impelled Dr. Jo Freudenheim of the University of Buffalo to check if an association with breast cancer could be found too. She found it, in a large-scale study that involved monitoring almost 74,000 postmenopausal women who had enrolled in the Women's Health Initiative Observational Study.
None of the women in the study had a personal history of breast cancer but over a quarter (26.1%) had gum disease (self-reported), says Freudenheim in Cancer Epidemiology, Biomarkers & Prevention.
Because prior studies have demonstrated that that gum infection can have greater implications for health among smokers, the researchers examined the associations broken down by smoking status.
After a period of 6.7 years, on average, 2.8% of the women, or 2,124, had developed breast cancer.
Crunching the numbers led to the conclusion that the risk of breast cancer was 14 percent higher in women who had periodontal disease.
Among women who had quit smoking within the past 20 years, those with periodontal disease had a 36 percent higher risk of breast cancer.
Women who were smoking at the time of this study had a 32 percent higher risk if they had periodontal disease. Those who had never smoked and had quit more than 20 years ago had a 6 percent and 8 percent increased risk, respectively, if they had periodontal disease.
"We know that the bacteria in the mouths of current and former smokers who quit recently are different from those in the mouths of non-smokers," Freudenheim said in a statement.
Why might periodontal disease affect breast cancer rates? We don't know, nor do we really know why it affects other cancers. One theory is that because it affects the bacterial flora of the mouth, it affects the bacteria entering circulation in the body. However, further studies are needed to establish a causal link, Freudenheim said.
Another more general theory is that bacterial infection of the mouth's tissues is accompanied by inflammation – which is simply the body's rather complex immune response to bad things, from bacteria to cell damage. The problem is when inflammation turns chronic, in which case it has been linked to increased probability of a host of deadly diseases, including cancers, diabetes and even stroke and Alzheimer's.