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Mouthwash Cancels Out Key Benefits of Exercise, Study Finds

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Your mouthwash could have a bizarre effect on how exercise affects your body, a new study this week suggests. The study found that swigging mouthwash can prevent exercise from lowering your blood pressure as it normally does. Strange as that sounds, the results highlight just how important the bacteria living in our mouths really are to us.

According to study author Raul Bescos, a nutritional physiologist based at the University of Plymouth in the UK, his team wasn’t really interested in studying mouthwash’s effects on exercise by itself.


It’s been long known that exercise opens up and dilates our blood vessels, in part by getting our bodies to produce more nitric oxide. But even after we’re done jogging and stop producing excess nitric oxide, our circulation is still affected, with our blood pressure remaining lower than it was for hours—a phenomenon known as post-exercise hypotension. There are various theories for why this happens, but no one’s completely figured it out.

One theory Bescos and his team had, based on other research, involves the natural microbial environment, or microbiome, of our mouths. A byproduct of nitric oxide, called nitrate, is often gobbled up by certain mouth bacteria. These bacteria then process nitrate into another chemical called nitrite, which is absorbed into the body when we swallow saliva, and some of it is again turned back into nitric oxide. They theorized that this process gets enough nitric oxide back into our bloodstream where it helps keep our blood pressure low. Mouthwash was simply a way for them to test out their theory. They used antibacterial mouthwash containing chlorhexidine, a potent antiseptic used in many prescription strength and some over-the-counter mouthwashes.


“We used this approach because we had evidence that it was an effective method to inhibit the activity of oral bacteria, and more particularly the nitrite synthesis in the mouth,” Bescos told Gizmodo via email.

The team recruited 23 healthy adults for their experiment. They had the volunteers run on a treadmill for a half-hour on two separate occasions, then they were kept under close watch and had their blood pressure monitored for two hours. During those two hours, they were randomly assigned to periodically swig either mouthwash or a placebo; on the second trip, they took whichever liquid they hadn’t the first time around.


When people took mouthwash as opposed to placebo, the team found, their blood pressure wasn’t lowered by as much. And by the two-hour mark, the post-exercise effect had disappeared completely. The mouthwash didn’t likely kill off bacteria en masse in the mouth since the diversity of the microbiome was left unchanged. But it did seem to drastically reduce their ability to produce nitrite, and that led to lower levels of nitrite in people’s saliva and blood.

The team’s findings were published in Free Radical Biology and Medicine.

Other studies have already shown that mouthwash can impede nitrite production from our mouth bacteria, Bescos said. “However, this study shows for the first time that this oral nitrate/nitrite pathway is a key element on the cardiovascular benefits of exercise.”


Of course, as Bescos noted, most people probably aren’t downing a bottle of mouthwash every time they finish a jog. But there are some broader implications of their research (provided their results hold up with other, larger studies).

For one, we know that some people with high blood pressure have trouble lowering it even when they seem to be following their doctor’s advice and exercising more. People with high blood pressure might also be more likely to have gum disease, which could affect their oral microbiome. So it’s not implausible to think that the latter condition might be affecting their blood pressure, though more research is needed to prove that link, Bescos said.


And while mouthwash wasn’t the key part of his team’s study, other research this year has suggested that regular use can possibly even raise blood pressure in people, rather than just weaken the benefits of exercise. As with this study, the authors theorized this effect was caused by how mouthwash affected the bacteria capable of producing nitrite.

Given all this, it’s worth studying further whether mouthwash is really doing more good than bad for us. But above all, Bescos said, the study is just added evidence that our oral health is more connected to our lives than we assume it to be.


“The main message of this study is that we have to pay more attention to the oral conditions in order to get the maximum outcomes from exercise,” he said.

Clarification: We have changed the headline to emphasize that the finding is from a single study.