Mouthwash and exercise

Mouth bacteria play a key role in our health. Previous studies have found strong association between bacteria that cause gum disease, and both a higher risk of esophageal cancer, and higher risk of dementia. The role of mouth bacterium in speeding up the growth of colorectal tumors and in impairing respiratory health have also been observed.

With so much negative connotations associated with mouth bacterium, researchers at the University of Plymouth in the United Kingdom were pleasantly surprised to discover the positive role of oral bacteria in ensuring cardiovascular benefits from exercise. The scientists found that mouth bacteria play a crucial role in mediating and maintaining the blood pressure-lowering effects of exercise, and that the use of antibacterial mouthwash interfered with this process.

Scientists already knew that blood vessels open up during exercise, as the production of nitric oxide during exercise increases the diameter of the blood vessels (known as vasodilation), thereby increasing blood flow circulation to active muscles.

However, it remained a mystery about how blood circulation remains higher even after a bout of exercise resulting in triggering a blood pressure-lowering response known as post-exercise hypotension.

Explaining the mechanism behind the post-exercise hypotension, researchers said that studies over the last decade have shown that nitrate can be absorbed in the salivary glands and excreted with saliva in the mouth. 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.

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.

In their new study the researchers wanted to know whether blocking nitrate’s ability to convert into nitrite by inhibiting oral bacteria, through the use of mouthwash, would have any effect on post-exercise hypotension.

Nearly two dozen healthy adults were recruited 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 ensured that neither the testers nor the participants knew who was receiving mouthwash and who was using a placebo.

The study 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 post-exercise. 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 percent in the first hour of post-exercise recovery and canceled them completely after 2 hours.

The new study also challenged earlier views that nitric oxide was not involved in the post-exercise response. 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. If they are removed, nitrite cannot be produced, and the vessels remain in their current state.

Research in this area could improve our knowledge for treating hypertension — or high blood pressure — more efficiently, said the researchers.