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Research indicates mouthwash may impede benefits of exercise

A new study has shown that the use of mouthwash after exercising may impede blood pressure reduction in comparison to rinsing one's mouth with water. (Photograph: GP Studio/Shutterstock)

Mon. 9. September 2019


PLYMOUTH, UK: The systemic health benefits of regular exercise are myriad and well documented, and much the same could be said about the use of mouthwash. The latter, however, may negatively affect blood pressure reduction—a common advantage of exercise—according to a recent study by researchers from the University of Plymouth and the Centre for Genomic Regulation in Barcelona in Spain.

For the study, 23 adults with good oral health ran on a treadmill for 30 minutes on two separate occasions and were thereafter monitored for 2 hours. On each occasion, the participants were asked to rinse their mouths with a liquid at 1, 30, 60 and 90 minutes after cessation of the exercise. The liquid was either a mouthwash with a 0.2% concentration of chlorhexidine or a placebo of mint-flavoured water, and the participants were not informed which liquid they were rinsing with.

The study showed that, when participants rinsed with water, the average reduction in systolic blood pressure was –5.2 mmHg at 1 hour after exercise. However, when participants rinsed with the mouthwash, the average systolic blood pressure after 1 hour was –2 mmHg.

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Previous research has suggested that the main source of nitrite in blood after exercise is nitric oxide formed during exercise in the endothelial cells. However, this new study challenges this, since the blood nitrite levels of the participants who rinsed with mouthwash did not increase after exercise. Instead, it was only in the participants who ingested the placebo water that blood nitrite levels rose, indicating that oral bacteria are a key source of this molecule—at least during the immediate period of post-exercise recovery.

Based on these findings, the researchers recommend that health professionals should pay attention to the oral environment when advocating for interventions involving physical activity to reduce high blood pressure.

“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,” said Craig Cutler, a researcher at the University of Plymouth and co-author of the study.

“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,” Cutler continued.

“The next step 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. Long-term research in this area may improve our knowledge for treating hypertension more efficiently,” Cutler concluded.

The study, titled “Post-exercise hypotension and skeletal muscle oxygenation is regulated by nitrate-reducing activity of oral bacteria”, was published online in the November 2019 issue of Free Radical Biology and Medicine.

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