Bacteria seen in periodontal disease has also been found in liver cancer cells, say researchers at Queen's Hospital in Belfast.
Liver cancer, or hepatobiliary cancer, seems to be the only gastrointestinal cancer linked to gum disease. There didn't seem to be a raised risk for liver, colon, rectum or pancreatic cancers.
The researchers tracked the health of 469,628 people, 4,069 of whom developed liver cancer during the six years of the study. Poor oral health was reported in 13 per cent of the cases and most were young, female and living in socially deprived areas.
The researchers weren't sure why periodontal disease should be linked only to liver cancer, and not to other gastrointestinal cancers, but one theory is that the liver was diseased before the cancer appeared and was unable to properly process bacteria, which, in turn, triggered the start of the cancer.
Liver cancer is the sixth most lethal cancer, with a poor survival rate of just 11 per cent. Smoking, alcohol and obesity have all been linked to the cancer in the past.