"Why brushing your teeth could reduce your risk of throat cancer by more than one-fifth, study finds," the Mail Online reports. Researchers found that the quantity of one species of bacteria in the mouth could predict the chances of people developing oesophageal cancer (not throat cancer, as the Mail reports).
The oesophagus is the tube that takes food from the mouth to the stomach. Oesophageal cancer is becoming more common and around 8,900 people in the UK are diagnosed with it each year. There are two types of oesophageal cancer, oesophageal adenocarcinoma (more common in the UK) and oesophageal squamous cell carcinoma (more common in developing countries).
Oesophageal adenocarcinoma is more common among people who smoke, drink alcohol or are obese. This study shows that the bacteria in the mouth may also have an effect (although we don't know if that's a direct effect or caused by something else, such as inflammation from gum disease).
A type of bacteria that causes gum disease, called Tannerella forsythia, was more common in people who went on to develop oesophageal adenocarcinoma. Good oral hygiene, including regularly brushing and flossing your teeth, helps to keep teeth and gums healthy. This study suggests it may also help to protect against one type of cancer.
Read more advice about keeping your teeth, mouth and gums healthy.
Where did the story come from?
The study was done by researchers from New York University, the Department of Veterans Affairs New York Harbor Healthcare System, the National Cancer Institute, and the American Cancer Society, all in the US. It was funded by the National Cancer Institute and published in the peer-reviewed journal Cancer Research (not to be confused with the UK charity of the same name).
The Mail Online said that tooth-brushing can reduce the risk of oesophageal cancer by one-fifth. That’s a big jump from the study data, which found risk of cancer was increased by 21% in people who had double the average amount of Tannerella forsythia bacteria. Tooth-brushing is undoubtedly a good idea, but we don’t know whether it would have reduced the levels of bacteria found in these people, or whether that would have directly cut their risk of cancer.
What kind of research was this?
The study was a case control study, nested within two larger cohort studies. Researchers wanted to know whether oral bacteria differed between people who went on to get oesophageal cancer, and those who did not.
This type of study is useful for spotting links between factors, such as bacteria in the mouth and oesophageal cancer. But it can't prove that one factor causes the other.
What did the research involve?
Researchers used data from adults taking part in two big cohort studies looking at cancer risk (the National Cancer Institute Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial and the American Cancer Society Cancer Prevention Study II). They had all given samples of saliva at the start of the studies.
The researchers analysed the saliva samples using gene sequencing. This technique assesses biological samples to identify different species of bacteria.
They then compared results from each sample of people who later got oesophageal cancer, with samples from two people the same age and sex who didn't get cancer. Incidence of oesophageal cancer was determined by annual questionnaires sent in the post and verified by medical records.
All the participants had given samples by swilling a mouthwash around their mouths then spitting it into collecting tubes. The researchers extracted genetic information and sequenced it using a database of human oral bacteria.
Researchers adjusted the figures to take account of potential confounding factors including body mass index, smoking status, alcohol consumption level and consumption of fruit and vegetables.
What were the basic results?
Researchers found 81 people with oesophageal adenocarcinoma and 25 with oesophageal squamous cell carcinoma. The results differed for the two types of cancer:
- People with double the average amount of Tannerella forsythia had a 21% higher risk of oesophageal adenocarcinoma (odds ratio (OR) 1.21, 95% confidence interval (CI) 1.01 to 1.46).
- People with higher levels of Porphyromonas gingivalis may have had a higher risk of oesophageal squamous cell carcinoma but the numbers are too small to be sure this was not a chance finding (OR 1.30, 95% CI 0.96 to 1.77).
No other types of bacteria were linked to cancer risk with data strong enough to be sure.
How did the researchers interpret the results?
The researchers say their results showed a "biologically plausible" way in which bacteria might affect risk of two types of oesophageal cancer. They say more research is required, but that this opens the possibility of "modulating the oral microbiota [changing the bacteria in the mouth]" to prevent oesophageal cancer.
There's no doubt that keeping your teeth and gums healthy is sensible. We know good oral hygiene can prevent tooth decay and gum disease, and research also suggests it may help to keep the heart healthy. This new research suggests it could potentially help protect against one type of oesophageal cancer.
However, there are reasons to be cautious. The study only looked at a small number of people with each type of oesophageal cancer. It found statistically significant results for just one type of bacteria, despite looking at many others.
The researchers didn't have information about whether people had gum disease or gastro-oesophageal reflux disease. Both these diseases might have affected the bacteria in people's mouths and their chances of getting oesophageal cancer. We already know that gum disease has been linked to a range of conditions, ranging from tooth loss to heart attacks and stroke.
So, we can't say from this study that brushing your teeth prevents cancer. But we do know it helps avoid toothache, bad breath, gum disease, tooth decay and cavities. If it also helps to prevent one type of cancer, that's a bonus.
Find out more about how to look after your teeth.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Mail Online, 4 December 2017
Links to the science
Cancer Research. Published online December 3 2017