Here’s why you may want to skip the mouthwash

By Liz Meszaros, MDLinx
Published September 17, 2019

Key Takeaways

You may want to think twice before you take that morning swish of mouthwash. Your oral microbiome and the bacteria it houses may be more important to heart health than we ever thought.

In fact, using antibacterial mouthwash may significantly reduce the blood pressure-lowering effects of exercise, according to a recent study published in Free Radical Biology and Medicine. This effect—researchers are beginning to learn—may be dependent on oral bacterial species and their use of nitrate.

And, because so many Americans have hypertension—29% or 1 in every 3 adults, according to the CDC—and use mouthwash, these results carry particular weight.

“This is an important finding for public health because mouthwash is commonly used by the general population including patients with hypertension. Sales of antibacterial mouthwash and dental rinse products in the US was estimated at $1.4 billion in 2014,” noted the authors.

Exercise and nitric oxide

When we exercise, production of nitric oxide causes vasodilation, increasing circulation to the muscles. But after exercise, for unknown reasons, this response persists and triggers post-exercise hypotension. 

“Previous research has suggested that nitric oxide was not involved in this post-exercise response—and only involved during exercise—but the new study challenges these views,” said senior author Raul Bescos, PhD, lecturer, Nutritional Physiology, Institute of Health and Community, University of Plymouth, Plymouth, United Kingdom.

In addition, the oral microbiome plays an important role in the production and use of nitric oxide.

“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. 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,” explained Dr. Bescos.

Thus, the impetus for this study was to determine whether blocking the conversion of nitrate to nitrite by inhibiting oral bacteria would affect post-exercise hypotension.

For the study, 23 healthy adults (15 men, 8 women) were required to run on a treadmill at moderate intensity for 30 minutes on two separate occasions. They were monitored for 2 hours after each set, and were not allowed any food or drink except water during the exercise and observation periods. Participants were then randomized to rinse their mouths with either antibacterial mouthwash (0.2% chlorhexidine) or a mint-flavored placebo for 1 minute after 1, 30, 60, and 90 minutes of exercise.

They returned after a 1-week washout period, and were crossed over to the opposite protocol (mouthwash or placebo) for the second set of exercise. Both sets of tests were done on the same day of the week and at the same times (within about 2 hours) to reduce any possible effects caused by circadian fluctuations. Blood pressure levels were measured for all participants before exercise, and then again at 60 and 120 minutes post-exercise. Saliva and blood samples were obtained from 15 participants before exercise and 120 minutes after exercise. 

One hour after exercise, those who rinsed with the antibacterial mouthwash had a reduction of only 2.0 mmHg from their baseline blood pressure levels compared with a 5.2-mmHg reduction in those who did not rinse with the mouthwash. This comprised a stunning ~60% diminishing of the blood pressure-lowering effects of exercise.

By hour 2 post-exercise, in those who rinsed with antibacterial mouthwash, there was a complete absence of any blood pressure-lowering effects, and this was associated with a lack of change in circulatory nitrite and impaired microvascular response.

In those who rinsed with placebo, circulatory nitrates were increased by 100 nM at 2 hours post-exercise vs 59 nM at baseline (P=0.013), as was peak tissue oxygenation index (86.1 vs 84.8; P = 0.010).

Although the nitric oxide formed by the endothelial cells during exercise were previously believed to be the main source of nitrite in the circulation after exercise, this was not the case in this study. Participants who rinsed with antibacterial mouthwash did not demonstrate increased nitrite levels, as those who rinsed with placebo did. Thus, oral bacteria may be a key source of nitrite for the body directly 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,” said co-author Craig Cutler, doctoral candidate, 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.”

They have specific plans for what their next steps are:

“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. 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—or high blood pressure—more efficiently,” concluded Cutler.

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