Surprising new research shows that antibacterial mouthwash can limit the cardiovascular benefits of exercise. The effect of mouthwash on mouth bacteria interferes with a complex molecular mechanism that usually sustains the blood pressure-lowering effects of exercise.

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Antibacterial mouthwash may help oral health, but new research shows that it interferes with the cardiovascular benefits of exercise.

The bacteria in our mouths play a key role in our health. An analysis of oral microbes from tens of thousands of people, for example, found an association between bacteria that can cause gum disease and a higher risk of esophageal cancer.

Other studies have exposed the mechanism by which a mouth bacterium can speed the growth of colorectal tumors and shown how oral bacteria can impair respiratory health. Finally, some research has also linked gum disease with higher dementia risk.

New research zooms in on another fascinating role that oral bacteria play in our health — namely, that they help us get cardiovascular benefits from exercise.

Raul Bescos, a lecturer in dietetics and physiology at the University of Plymouth, United Kingdom, is the lead author of the new study, which shows how mouth bacteria mediate the blood pressure-lowering effects of exercise and how the use of antibacterial mouthwash interferes with this process.

The new paper appears in the journal Free Radical Biology and Medicine.

Nitric oxide, nitrate, and nitrite

The study's lead author explains the motivation for the new research, saying, "Scientists already know that blood vessels open up during exercise, as the production of nitric oxide increases the diameter of the blood vessels (known as vasodilation), increasing blood flow circulation to active muscles."

"What has remained a mystery is how blood circulation remains higher after exercise, in turn triggering a blood pressure-lowering response known as postexercise hypotension."

Nitric oxide breaks down into nitrate, explains Bescos. This process is the beginning of a circular molecular reaction, which, in the end, results in the sustained blood pressure-lowering effects of exercise.

"[R]esearch over the last decade has shown that nitrate can be absorbed in the salivary glands and excreted with saliva in the mouth," explains Bescos. "Some species of bacteria in the mouth can use nitrate and convert [it] into nitrite — a very important molecule that can enhance the production of nitric oxide in the body."

"And when nitrite in saliva is swallowed, part of this molecule is rapidly absorbed into the circulation and reduced back to nitric oxide. This helps to maintain a widening of blood vessels, which leads to a sustained lowering of blood pressure after exercise."

"We wanted to see whether blocking nitrate's ability to convert into nitrite by inhibiting oral bacteria [through the use of mouthwash] would have any effect on postexercise hypotension."

Raul Bescos

How mouthwash reduces exercise benefits

To find out, Bescos and team asked 23 healthy adults to participate in two acute bouts of exercise. For each of these, the participants ran on a treadmill for 30 minutes, and the researchers monitored the participants' blood pressure for 2 hours after the exercise.

At 1, 30, 60, and 90 minutes after the run, the participants rinsed their mouths with either antibacterial mouthwash or the control substance, which was mint flavored water. The team also collected blood and saliva samples just before exercise and 2 hours after.

The team used "a randomized, double blind and crossover [study] design," meaning that neither the testers nor the participants knew who was receiving mouthwash and who was using a placebo.

The trial revealed that the placebo intervention resulted in an average reduction of 5.2 milligrams of mercury (mm Hg) in systolic blood pressure at 1 hour postexercise. In contrast, rinsing with antibacterial mouthwash resulted in a reduction of only 2.0 mm Hg.

The results suggest that mouthwash reduced the blood pressure-lowering effects by more than 60% in the first hour of postexercise recovery and canceled them completely after 2 hours.

Also, "Previous research has suggested that nitric oxide was not involved in [the] postexercise response — and only involved during exercise — but the new study challenges these views," explains Bescos.

Challenging preexisting notions

The prevailing notion has been that the primary source of nitrite in the blood after exercise is nitric oxide that the body creates in endothelial cells during exercise. Endothelial cells are the cells that line the inside of blood vessels.

However, the results of the new study contradict this because blood nitrite levels did not rise after exercise in the participants who had used mouthwash. Blood nitrite levels only rose after exercise when participants rinsed with the control substance.

These findings indicate that mouth bacteria are the main source of circulating nitrite, at least in the recovery period immediately after exercise.

Study co-author Craig Cutler comments on the significance of the findings, saying: "[O]ral bacteria are the 'key' to opening up the blood vessels. If they are removed, nitrite can't be produced, and the vessels remain in their current state."

"These findings show that nitrite synthesis by oral bacteria is hugely important in kick-starting how our bodies react to exercise over the first period of recovery, promoting lower blood pressure and greater muscle oxygenation."

Craig Cutler

"The next step," continues Cutler, "is to investigate in more detail the effect of exercise on the activity of oral bacteria and the composition of oral bacteria in individuals under high cardiovascular risk."

"[In the L]ong term, research in this area may improve our knowledge for treating hypertension — or high blood pressure — more efficiently."