A link between bacteria commonly found in the mouth – such as that tannerella forsythia and porphyromonas gingivalis – and oesophageal cancer has been made by other scientists in previous studies.
Another possible reason is that poor oral hygiene and gum disease could promote the formation of bacteria known to cause gastric cancer, scientists said.
But mild cases of gum disease can commonly be treated with good oral hygiene, including brushing your teeth twice a day and flossing.
Previous findings on the relationship of gum disease and tooth loss with oesophageal and gastric cancer have been inconsistent, the authors said.
One observational study published in the BMJ Open journal in 2012 examined the link between dental plaque and premature cancer death.
After 24 years, 58 of the 1,390 participants had died, 35 as a result of cancer, and those who died had a significantly higher quantity of dental plaque than the survivors. But the authors warned their findings did not prove that plaque definitively causes cancer.
In this study, published in the journal Gut, the large sample size, long term follow up of the patients, and “rigorous control” for lifestyle impacts, adds strength to the findings, Dr Mingyang Song, Harvard T.H. Chan School of Public, told The Telegraph.
The authors concluded: “Together, these data support the importance of oral microbiome in oesophageal and gastric cancer.
“Further prospective studies that directly assess oral microbiome are warranted to identify specific oral bacteria responsible for this relationship.”
Dr Song said they are planning future studies to examine the role of oral microbiome in the development of upper gastrointestinal (GI) cancers, which include oesophageal, stomach, small bowel cancer, pancreatic, and liver cancers.
“The goal is to identify the specific microbes in the oral cavity and related mechanisms that may contribute to the risk increase of upper GI cancers in people with gum disease.
“This research will ultimately lead to new microbiome-based prevention strategies for these cancers,” he said.