A small randomized placebo-controlled trial finds the blood pressure-lowering effect of exercise was diminished by 61% during the first hour of recovery, and completely abolished 2 hours after exercise when participants were given antibacterial mouthwash.

Part of the blood-pressure-lowering effect of exercise has to do with increased levels of nitrate and subsequently nitric oxide which causes vasodilatation. When antibacterial mouthwash was given to the participants, their blood nitrite levels did not increase after exercise. It was only when participants used the placebo that nitrite levels in blood raised, suggesting that oral bacteria may play a role in nitrate levels in the circulation at least over the first period of recovery after exercise.

The antibacterial mouthwash used was 0.2% chlorhexidine. This was a small trial (23 participants) so no definitive conclusions can be made but these results are interesting and should be further explored.