Ingested Nitrate and Nitrite: Beneficial to Human Health?

抄録

Nitrate and nitrite are products of the oxidation of nitrogen by microorganisms in plants, soil and water. The amount of nitrate in the environment has increased dramatically since the Industrial Revolution, primarily due to the use of fossil fuels and the production of artificial fertilizers. This increase has led to a number of environmental problems, including the accumulation of nitrate in both freshwater and coastal marine ecosystems and increased levels of stratospheric nitrous oxide (N₂O), the most important ozone-depleting substance emitted in the 21st century. Human exposure to nitrate and nitrite occurs primarily through ingestion of food, particularly leafy vegetables, and water. Nitrate can be reduced in the body to nitrite, which can react under acidic conditions with nitrosatable amino compounds to form potentially carcinogenic N-nitroso compounds. Some epidemiological studies have indicated a possible association between various cancers and the ingestion of nitrate and nitrite in drinking water and food. Other recent studies have revealed that nitrate and nitrite can be reduced in vivo to nitric oxide (NO), especially during the stress of hypoxemia and ischemia. In a variety of animal models, the reduction of nitrite to NO suppresses apoptosis and cytotoxicity at reperfusion in the mammalian heart, liver, kidney, and brain. Because vegetables often contain large amounts of nitrate and have protective effects against coronary heart diseases, some investigators have claimed that nitrate and nitrite are responsible for their beneficial effects. However, this speculation should be interpreted cautiously, because the physiological and pathophysiological roles of ingested nitrate and nitrite at high doses remain unclear. We discuss the beneficial and hazardous aspects of ingested nitrate and nitrite in human health.