Woman with toothache brushing her teeth (© LIGHTFIELD STUDIOS - stock.adobe.com)
NEW YORK — Scientists have found another reason why everyone should brush and floss their teeth. Beyond avoiding cavities and gum disease, good oral hygiene also protects against head and neck cancer. A new study has found that over a dozen species of bacteria are linked to a 50% higher risk of developing head and neck cancer. These same germs have been tied to periodontal disease, a severe gum infection that can damage the jawbone and soft tissue around teeth.
For a long time, experts have observed a strong relationship between people with poor oral health and being more prone to cancers of the mouth and throat. Prior studies have identified bacteria in the mouth to these types of cancers, but until now, it has been unclear what kinds of bacteria were involved. The results are published in the journal JAMA Oncology.
“Our findings offer new insight into the relationship between the oral microbiome and head and neck cancers,” says Soyoung Kwak, a postdoctoral fellow in the Department of Population Health at the NYU Grossman School of Medicine, in a media release. “These bacteria may serve as biomarkers for experts to flag those at high risk.”
Researchers looked at data from three ongoing studies tracking 159,840 Americans across the nation and how their diet, lifestyle, medical history, and other factors affect their risk for cancer later in life. The analyses from these studies gave scientists the first opportunity to see whether bacteria and other microbes commonly in the mouth, such as fungi, can influence head and neck cancer risk.
The study participants were instructed to rinse with mouthwash and provide saliva samples so that researchers. The team used the saliva samples to identify the DNA of bacteria and fungal species, which allowed them to measure the number and types of microbes in the mouth.
After 10 to 15 years, the researchers contacted the study participants again to record any tumors that had developed during that time. A total of 236 people were diagnosed with head and neck cancer.
The researchers then compared the oral health of the 236 diagnosed with head and neck cancer with 458 randomly selected study participants without cancer. They also considered people’s race, age, and how often they smoked cigarettes or drank alcohol in their analysis. Thirteen bacterial species in the mouth, including Prevotella salivae, Streptococcus sanguinis, and Leptotrichia, were associated with an increased risk of head and neck cancer. There were no oral fungal species that displayed a connection to head and neck cancer risk.
“Our results offer yet another reason to keep up good oral-hygiene habits,” says study senior co-author Richard Hayes, a professor at the NYU Grossman School of Medicine and member of the Perlmutter Cancer Center. “Brushing your teeth and flossing may not only help prevent periodontal disease, but also may protect against head and neck cancer.”
While the study identified several correlations between cancer risk and specific bacterial species in the mouth, the authors emphasize that this does not mean having these bacteria will automatically cause a person to have head and neck cancer. Additionally, they emphasize that head and neck cancer is still very uncommon. The next step is to look for possible mechanisms to explain how these bacteria are involved in head and neck cancer. Understanding the mechanisms can open up new ways to treat and possibly prevent head and neck cancer for at-risk individuals.
Paper Summary
Methodology
The researchers conducted a prospective study to see if the bacteria and fungi living in our mouths (called the “oral microbiome”) were linked to the future risk of developing head and neck squamous cell cancer (HNSCC). They used oral samples from three large U.S. cohorts — groups of people who are followed over time to track their health. They compared 236 people who later developed HNSCC to 485 people who did not, matching them by age, sex, race, and other factors. They then used advanced DNA sequencing techniques to identify the types of bacteria and fungi in their mouths. Statistical analyses were performed to see if specific bacteria or fungi were more common in people who developed HNSCC than in those who didn’t.
Key Results
The study found that while the diversity of the overall oral microbiome didn’t seem to affect the risk of HNSCC, 13 specific types of bacteria were linked to it. Some bacteria were associated with a lower risk of developing the cancer, while others increased the risk. For example, bacteria like Prevotella salivae and Streptococcus sanguinis appeared to protect against the cancer, while certain species linked to gum disease (like Porphyromonas gingivalis) increased the risk. The study found no link between fungi and HNSCC risk.
Study Limitations
Due to this study being observational, meaning the researchers watched what happened without trying to change anything, it’s possible that other unmeasured factors could have influenced the results. For example, oral health or other lifestyle factors might also contribute to cancer risk. Also, while the study used a large number of participants, it didn’t capture the relationships between bacteria, fungi, and cancer in every possible situation. The findings related to fungi were also limited, as the study may not have captured the full role of fungi in the development of HNSCC.
Discussion & Takeaways
The study provides important evidence that certain bacteria in the mouth are linked to an increased risk of developing head and neck cancer, even years before the cancer appears. This suggests that in the future, doctors could potentially use information about a person’s oral bacteria to help identify those at higher risk for these cancers, especially if other risk factors like smoking or poor oral health are present. The study also suggests that improving oral health and reducing harmful bacteria could lower the risk of developing HNSCC. However, more research is needed to fully understand the mechanisms involved and to see how these findings could be applied to cancer prevention.
Funding & Disclosures
This study was supported by several grants from the National Cancer Institute (NCI) and the National Library of Medicine, along with funding from the American Cancer Society, which helped maintain the cohort studies. The samples were analyzed at the Genome Technology Center at NYU School of Medicine. One of the researchers, Dr. Richard B. Hayes, reported receiving grants from the National Institutes of Health (NIH) outside the study. No other significant conflicts of interest were reported by the authors.
