Dear Doctors: I thought brushing your tongue was an important part of oral hygiene. But a friend who is a nurse says it’s not a great idea. She said it has something to do with the mouth microbiome and high blood pressure. I didn’t even know the mouth had a microbiome. Can you explain?

Dear Reader: Although the microbiome we hear about most often is located in the gut, these communities are found throughout the body. The word “microbiome” refers to a distinct collection of microorganisms that are living together in a common habitat. And it’s not only humans that play host to microbiomes. They are found in all animals, as well as plants, soil and bodies of water. Even built environments – such as a house, car or office building – have a unique microbiome.

When it comes to the human mouth, the number and diversity of microorganisms it contains is second only to the gut. The bacteria, fungi, benign viruses and protozoa it contains are crucial to oral and systemic health. As a result, researchers are now exploring the roles the estimated 700 unique species of bacteria in the oral cavity play in health and wellness. Among their findings is an intriguing link to blood pressure regulation.

The focus here is a molecule known as nitric oxide. It is produced by cells throughout the body and plays a crucial role in promoting blood flow. Known as a vasodilator, nitric oxide helps keep blood vessels relaxed and pliable. This lowers the pressure that circulating blood exerts on the walls of the veins, arteries and capillaries. And that brings us to the research your friend was referring to when she suggested there may be a downside to brushing your tongue.

Several studies have found that certain microbes that live on the back portion of the tongue convert a nutrient found in plant-based foods into nitrites. This results in the production of nitric oxide, which is beneficial to heart and circulatory health. The nutrient that the tongue bacteria convert is called dietary nitrate. It’s found primarily in green leafy vegetables such as spinach, lettuce and bok choy, and in root vegetables such as carrots and beets.

Some researchers have linked the role of the mouth microbiome in converting dietary nitrate to nitric oxide to the positive health effects of the Mediterranean diet. They suggest that brushing or scraping the tongue adversely affects the numbers and diversity of the oral microbiome. This, in turn, reduces or even eliminates an important source of nitric oxide, and can lead to hypertension.

A study at the University of Texas adds to the evidence. The researchers found that when volunteers used an antiseptic mouthwash twice a day, which weakened the oral microbiome, their blood pressure rose. When the mouthwash was discontinued a week later, blood pressure returned to normal.

So far, this all remains theoretical. But with such a promising line of inquiry, we expect to hear more about it the future.

Send your questions to askthedoctors@mednet.ucla.edu.