Did you know that your tongue is an erection engine – no it’s not what you think – responsible for much of the nitric oxide production in your body? Yes, much of health is counterintuitive and this is yet another example.
It turns out that bacteria on the tongue converts any nitrates you eat into nitrities. These nitrites are in turn transported down the throat via saliva and, when they hit the acid in the stomach, are eventually transformed into the all-important nitric oxide that is responsible for your erections. 
Furthermore, in my Interview with Dr. Nathan Bryan, he explains how this is actually a very efficient pathway for middle-aged and older males, much more efficient, for example, than the standard L-Arginine process that so many supplements go after. My book, The Peak Erectile Strength Diet, discusses some of the higher nitrate foods for just this reason.
There is one thing that can easily sabotage your body’s natural efforts to produce nitric oxide: many men consume mouthwashes that kill the nitrate-to-nitrite converting bacteria on your tongue. That’s right – most mouthwashes are 25 percent alcohol – and swishing that stuff around in your mouth kills just about everything, both good and bad. With it goes the good bacteria that you need so badly.
Interestingly enough, this was shown clearly in a study of cancer-related issues.  Researchers have long known that processed meats, which are high in nitrate additives as a preservative, lead to increased rates of GI cancer. Scientists speculate that it may be because nitrates, under certain conditions, can lead to increased levels of nitrosamines, compounds that have been associated with increased cancer risk. What this study looked at was whether or not mouthwash, by killing tongue bacteria, of course would decrease nitrite levels.
So, if you have gingivities or periodontal disease, you might want to discuss different possibilities with your dentist.
CAUTION: One study linked a 60 and 40 percent increase in oral cancer in women and men, respectively, to mouthwash usage.  Other studies, however, have not found the same result. However, some experts would argue that smokers and drinkers need to be particularly careful.
2) Cancer Detect Prev, 1998, 22(3):204-12, “Formation of nitrosamines during consumption of nitrate- and amine-rich foods, and the influence of the use of mouthwashes”
3) Cancer Res, Jun 1 1991, 51:3044, “Mouthwash Use and Oral Conditions in the Risk of Oral and Pharyngeal Cancer”