One of the benefits of exercise is improved cardiovascular function, and one of the ways in which this manifests is a reduced blood pressure. Maintaining a lower blood pressure is very influential over the course of aging; age-related hypertension is very damaging. Exercise tends to exhibit short term benefits immediately following a session, and then similar long term benefits when exercise is regular. Here, researchers show that the short term reduction in blood pressure following exercise is mediated in large part by oral bacteria, a most interesting finding. Whether this holds up over the long term and regular use of antibacterial mouthwash at times unrelated to exercise is another question entirely, of course. If anything, modern dentistry is the story of a futile struggle to keep any sort of oral bacteria population suppressed for any length of time.
Scientists 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. 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. 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.
"It's all to do with nitric oxide degrading into a compound called nitrate, which for years 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. 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."
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 per cent chlorhexidine) or a placebo of mint-flavoured water. Their blood pressure was measured and saliva and blood samples were taken before exercise and at 120 minutes after exercise. No food or drink except water was allowed during exercise and the recovery period, and none of the study participants had any oral health conditions.
The study found that 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. These results show that the blood pressure-lowering effect of exercise was diminished by more than 60 per cent over the first hour of recovery, and totally abolished two hours after exercise when participants were given the antibacterial mouthwash. 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.