Mouthwash Raises Blood Pressure?

Oral bacteria are the ‘key’ to opening up the blood vessels

Woman using mouthwash

Woman using mouthwash

Exercise is known to reduce blood pressure. But using the wrong mouthwash can undo all of its benefits, says a study from the University of Plymouth in collaboration with the Centre of Genomic Regulation in Barcelona (Gabaldon’s lab), Spain, and published in the journal Free Radical Biology and Medicine.

The international team of scientists found the blood pressure-lowering effect of exercise was markedly reduced when people rinsed their mouths with antibacterial mouthwash rather than water.

The bottom line: the activity of bacteria in our mouths may determine whether we experience optimal exercise benefits.

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“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,” explains lead author Dr. Raul Bescos, Lecturer in Dietetics and Physiology at the University of Plymouth. “What has remained a mystery is how blood circulation remains higher after exercise, in turn triggering a blood-pressure lowering response known as post-exercise hypotension.”

The research goes against earlier research that nitric oxide isn’t involved in this post-exercise response—and only involved during exercise—but the new study challenges these views.

Oral Bacteria Convert Nitrate

It all has to do with nitric oxide degrading into a compound called nitrate. For years, nitrate was thought to have no function in the body. But research over the last decade has shown that nitrate can be absorbed in the salivary glands and excreted with saliva in the mouth.

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“Some species of bacteria in the mouth can use nitrate and convert into nitrite-—a very important molecule that can enhance the production of nitric oxide in the body,” says Dr. Bescos. “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.”

Twenty-three healthy adults were asked to run on a treadmill for a total of 30 minutes on two separate occasions, after which they were monitored for two hours.

On each occasion at one, 30, 60 and 90 minutes after exercise they were asked to rinse their mouths with a liquid—either antibacterial mouthwash (0.2% chlorhexidine) or a placebo of mint-flavored water.

When participants rinsed with the placebo, the average reduction in systolic blood pressure was -5.2 mmHg at one hour after exercise. However, when participants rinsed with the antibacterial mouthwash, the average systolic blood pressure was -2.0 mmHg at the same time point. (Systolic blood pressure refers to the highest blood pressure level when the heart is squeezing and pushing the blood round the body.)

Exercise Diminished by 60%

These results show that the blood pressure-lowering effect of exercise was diminished by more than 60% over the first hour of recovery, and totally abolished two hours after exercise when participants were given the antibacterial mouthwash.

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Previous views also suggested that the main source of nitrite in the circulation after exercise was nitric oxide formed during exercise in the endothelial cells (cells that line the blood vessels). However, the new study challenges this. When antibacterial mouthwash was given to the participants, their blood nitrite levels did not increase after exercise. It was only when participants used the placebo that nitrite levels in blood raised, indicating that oral bacteria are a key source of this molecule in the circulation at least over the first period of recovery after exercise.

“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,” commented Craig Cutler, study co-author who conducted the research as part of his PhD at the University of Plymouth. “In effect, it’s like oral 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.

“Existing studies show that, exercise aside, antibacterial mouthwash can actually raise blood pressure under resting conditions, so this study followed up and showed the mouthwash impact on the effects of exercise.

ReferenceC. Cutler, M. Kiernan, J.R. Willis, L. Gallardo-Alfaro, P. Casas-Agustench, D. White, M. Hickson, T. Gabaldon, R. Bescos. Post-exercise hypotension and skeletal muscle oxygenation is regulated by nitrate-reducing activity of oral bacteria. Free Radical Biology and Medicine, 2019; 143: 252 DOI: 10.1016/j.freeradbiomed.2019.07.035
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