Dietary nitrate in man: friend or foe?

Abstract

Based on the premise that dietary nitrate is detrimental to human health, increasingly stringent regulations are being instituted to lower nitrate levels in food and water. Not only does this pose a financial challenge to water boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. It is recirculated in the blood, concentrated by the salivary glands, secreted in the saliva and reduced to nitrite by facultative Gram-positive anaerobes (Staphylococcus sciuriandS. intermedius) on the tongue. Salivary nitrite is swallowed into the acidic stomach where it is reduced to large quantities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitrite, mimicking gastric conditions, have been shown to have antimicrobial activity against a wide range of organisms. In particular, acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such asYersiniaandSalmonella.NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, which determines reactive nitrogen oxide species production in the stomach (McKnightet al.1997), is emerging as an effective host defence against gastrointestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitrate may have an important therapeutic role to play, not least in the immunocompromised and in refugees who are at particular risk of contracting gastroenteritides.

Selected physicochemical properties of amniotic fluid according to week of pregnancy

“…They are recirculated in the blood, concentrated in the salivary glands, secreted in saliva and reduced to nitrites by facultative Grampositive anaerobes (Staphylococcus sciuri and S. intermedius) on the tongue. Owing to the acidic stomach environment, the salivary nitrites are reduced to large quantities of nitric oxide (NO) and other oxides of nitrogen (16). NO is a potent vasodilator which plays a key role in the control of vascular tone and is released by endothelial cells from L-arginine.…”

Association of Nitrogen Compounds in Drinking Water with Incidence of Esophageal Squamous Cell Carcinoma in Shexian, China

“…Although NO 2 can be converted to nitrosamine in the stomach (McKnight et al 1999), the concentration of NO 2 in nature is too low to pose a problem in this respect (Table 1). Therefore, it is hard to consider environmental NO 2 as a risk factor, since even high-incidence ESCC areas do not have high concentrations of NO 2 (Fig.…”

“…van Loon et al (1998) showed that NO 3 has no harmful effect, even when intake is high. However, when NO 3 is assimilated in the body, it is converted to NO 2 by denitrifying bacteria, and NO 2 can subsequently be converted to nitrosamine in the stomach (McKnight et al 1999). Consequently, a high concentration of NO 3 will lead to a high incidence of ESCC.…”

A questão do nitrato em alface hidropônica e a saúde humana

“…Além disso, indicam que dietas ricas de saladas e vegetais e, portanto, alto conteúdo de nitrato são protetoras contra alguns tipos de câncer, particularmente câncer gástrico (ADDISCOTT & BENJAMIN, 2000;ARCHER, 2002). Porém, MCKNIGHT et al (1999) mostram que experimentos tentando ligar o aparecimento de câncer à dieta rica em nitratos têm demonstrado resultados contraditórios (Tabela 1).…”