Specific combinations of microbes living in our mouths have been associated with one of the deadliest cancers in humans, suggesting good oral hygiene could do more than just save our teeth.
"It is clearer than ever that brushing and flossing your teeth may not only help prevent periodontal disease but may also protect against cancer," explains cancer epidemiologist Richard Hayes from New York University (NYU).
The pancreas is an abdominal organ responsible for producing enzymes and hormones our bodies use to break down and absorb nutrients in our food. Though it rarely develops tumors, those who do develop the disease face a tragically low chance of surviving in the long term.
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Hayes, NYU epidemiologist Yixuan Meng, and colleagues used health records and oral wash samples collected through two studies involving more than 300,000 individuals aged in their fifties to seventies.
When considered collectively, 27 microbes identified in the mouth washes were linked to more than triple the risk of pancreatic cancer, a disease that strikes 1 in 56 men and about 1 in 60 women in the US at some point in their lives.
The team's findings, together with past research, suggest some of our mouth's microbes may be accessing the pancreas by travelling into the digestive system through our saliva.
The researchers identified three species of mouth bacteria in particular (Porphyromonas gingivalis, Eubacterium nodatum, and Parvimonas micra), and a common skin and gut fungus, Candida tropicalis, that were linked with the increased chance of a pancreatic cancer diagnosis.
Hayes cautions that while this doesn't necessarily mean the microbes they identified cause cancer directly, the patterns they observed highlight species that warrant further investigation. What's more, other Candida and bacterial species were associated with a decreased risk of cancer, suggesting the precise make-up of oral microflora is critical for our health.
The researchers puzzled out the microbe patterns using data from two long-term health studies in America: the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial and the American Cancer Society Cancer Prevention Study-II Nutrition Cohort.
About 445 of the participants in these studies developed pancreatic cancer. Their data was compared to 445 healthy controls.
"A bacteriome-wide scan revealed eight oral bacteria associated with decreased and 13 oral bacteria associated with increased risk of pancreatic cancer," the researchers write in their paper.
Pancreatic cancer survival rate is just 13 percent at five years, often due to late diagnosis. Symptoms don't usually reveal themselves until the disease is at an advanced stage, so understanding early risk factors, like mouth microbiome composition, could aid earlier detection.
"By profiling bacterial and fungal populations in the mouth, oncologists may be able to flag those most in need of pancreatic cancer screening," explains NYU epidemiologist Jiyoung Ahn.
The team aims to examine how viruses also contribute to these risks next.
This research was published in JAMA.