Dietary nitrate in man: friend or foe?

Based on the premise that dietary nitrate is detrimental to human health, i ncreasingly stringent regulations are being instituted to lower nitrate lev els in food and water. Not only does this pose a financial challenge to wat er boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Unt il recently nitrate was perceived as a purely harmful dietary component whi ch causes infantile methaemoglobinaemia, carcinogenesis and possibly even t eratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. I t is recirculated in the blood, concentrated by the salivary glands, secret ed in the saliva and reduced to nitrite by facultative Gram-positive anaero bes (Staphylococcus sciuri and S. intermedius) on the tongue. Salivary nitr ite is swallowed into the acidic stomach where it is reduced to large quant ities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitri te, mimicking gastric conditions, have been shown to have antimicrobial act ivity against a wide range of organisms. In particular, acidified nitrite i s bactericidal for a variety of gastrointestinal pathogens such as Yersinia and Salmonella. NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, whic h determines reactive nitrogen oxide species production in the stomach (McK night er al. 1997), is emerging as an effective host defence against gastro intestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitra te may have an important therapeutic role to play, not least in the immunoc ompromised and in refugees who are at particular risk of contracting gastro enteritides.