In a new study from BMJ, particular types of bacteria appear to be linked to heightened risk of lung cancer. Around one in four cases of lung cancer occurs in non-smokers. However the scientists say these statistics are not entirely explained by established risk factors such as second-hand smoke, exposure to radon in the background and air pollution.

The mouth is the starting point for bacteria in the lungs, so the researchers wanted to know if it might also be associated with lung cancer, because the mouth is a point of entry into the lungs.

Bacterial colonies grown on an agar plate in combination with iron powder. Product of a school work.
Photo by Adrian Lange / Unsplash

All participants in the study were life-long non-smokers. Their wellbeing was tracked every 2 or 3 years after they entered a study from 1996 to 2006. At registration, participants were rinsed to provide the residential bacteria with a profile and lifestyle, diet and medical history were provided with details as well as other environmental and occupational factors that could impact their disease risk.

In total, in 7 years, an average of 90 of the women and 24 of the men have developed lung cancer. Those cases were matched by 114 same age and sex non-smokers who also provided the sample for mouthwashing. This comparable community had no lung cancer, but had similar levels of education and lung cancer family history.

Comparison of both sets of rinse samples revealed that between the two groups the microbiome was different. The risk for lung cancer was decreased for a broader variety of bacterial species. And the risk of lung cancer is often associated with a greater volume of those fungi.