Does tongue scraping help improve nitric oxide production?
Research shows that the bacteria on your tongue convert nitrate from vegetables into a substance your body uses to make nitric oxide. Tongue scraping removes some of those bacteria, which can disrupt that process.
Bacteria on the tongue play a key role in producing nitric oxide. Nitrate from vegetables such as beetroot is converted by these bacteria into nitrite, and then into nitric oxide. This is a second route alongside the way the body produces this gas on its own, and both routes complement each other.
Tongue scraping removes bacteria from the surface of the tongue, which is precisely where nitrate-reducing bacteria live. None of the studies included tested tongue scraping directly, but antibacterial mouthwash, which knocks out the same bacteria, was tested. In five studies, the nitrite concentration in saliva consistently fell afterwards, and in four of the five, blood pressure rose. When the bacteria are removed, nitrite production drops and nitric oxide production appears to decrease.
Tongue scraping has not yet been directly tested in this research. But because the process runs through the same bacteria, it is plausible that vigorous scraping is more likely to disrupt nitric oxide production than to support it, especially if you eat nitrate-rich food shortly afterwards.
Whether the number of nitrate-reducing bacteria in your mouth is linked to your blood pressure over the long term remains unclear: 28 studies produced conflicting results, with some showing more, some fewer, and some no difference in these bacteria among people with high blood pressure. The simple picture of 'more beneficial bacteria is better' therefore does not straightforwardly hold.
This answer draws on four combined analyses of multiple studies and one study in people. The direct effect of tongue scraping on nitric oxide production has not yet been tested in people; the reasoning is based on studies of antibacterial mouthwash and the route through which nitrate passes from food via saliva into the body. The researchers themselves point to the absence of long-term studies on hard outcomes such as heart attacks, and to conflicting findings on the link between the mouth's bacterial environment and blood pressure.