Nitrate and human health

Nitrate is widely and mistakenly perceived to threaten human health by causing methaemoglobinaemia in infants and stomach cancer in adults, but it does cause environmental problems. Methaemoglobinaemia is a side-effect of gastroenteritis and is not caused by nitrate but by nitric oxide, which is produced in a defensive reaction stimulated by gastroenteritis. The latter may be caused by a bacterium or a virus. The association of methaemoglobinaemia with nitrate may have arisen because early cases of the condition were often associated with wells polluted with bacteria, and the same pollution increased the nitrate concentration. Four epidemiological studies sought a link between stomach cancer and nitrate but did not find one. The incidence of this cancer has also declined during the last 30 years, while nitrate concentrations in water have increased. Nitrate preserves, rather than threatens, health. It is reduced by microbes on the tongue to nitrite, which generates nitric oxide when acidified in an antibacterial defence mechanism vital to our well-being. This mechanism acts with great effectiveness in the stomach against Salmonella, Escherichia coli and other organisms that cause gastroenteritis. It also acts in our mouths against dental caries and even on our skin against fungal pathogens such as Tinea pedis (athlete's foot). This mechanism is the basis of the centuries-old practice of adding nitrate or nitrite to stored meat to protect against botulism, caused by the most lethal toxin known to mankind.