ADVANCEMENT OF THE SCIENCE - Report
New questions and insights into nitrate/nitrite and human health effects: a retrospective cohort study of private well users' immunological and wellness status.
IntroductionThe health effects of nitrate/nitrite ingestion are thought to be well established (Bricker, Jefferson, & Mintz, 1983; Comly, 1945; Fan & Steinberg, 1996; Johnson et al., 1987; Kristen, 2001; Levallois & Phaneuf, 1994; Szponar & Kierzkowska, 1990; Walton, 1951; Ward et al., 2005). When nitrate or nitrite is used as a preservative in prepared food stuffs, ingested, and digested in the presence of nitrosable amines, nitrosamines are formed. Nitrosamines are linked to human esophageal and gastric cancers in a variety of epidemiological studies (Andreassi et al., 2001; Fewtrell, 2004; Gulis, Czompolyova, & Cerhan, 2002). When nitrate contaminates well water used for human consumption, it is ingested and transformed by bacteria in the gut to nitrite, which interacts readily with the hemoglobin molecule of the red blood cell. This process removes electrons from the ferrous iron in the normally functioning hemoglobin and creates a ferric iron methemoglobin state, which does not readily bind with oxygen, causing a biochemical anemia (Gatseva et al., 2000; Gebara & Goetting, 1994; Knobeloch, Salna, Hogan, Postle, & Anderson, 2000; Sadeq et al., 2008). Since infants have small bodies but high water volume, they are very susceptible to the worst effects of acute nitrate toxicity due to the lower pH of the gut, an immature methemoglobin reductase system, high volume-to-surface-area ratios, and high ingestion rates of liquids. Biochemically induced "anemia," or infantile methemoglobinemia (iMHG), may result, which is not a loss of red blood cells but rather a lack of oxygen-carrying capacity (Abu Nasser, Ghbn, & Khoudary, 2007; Dagan, Zaltstein, & Gorodischer, 1988; Jolly, Monico, & McDevitt, 1995; Keating, Lell, Strauss, Zarkowsky, & Smith, 1973). As a result of these well-documented health concerns, environmental and public health regulatory agencies around the world have made efforts to encourage the removal of excess nitrate/nitrite salts from foodstuffs and have set limits for the amount of nitrate/nitrite found in drinking water. For example, the U.S. Environmental Protection Agency (U.S. EPA) maximum contaminant level (MCL) is 10 parts per million (ppm) nitrate-nitrogen (nitrate-N) (Fewtrell, 2004; Hegesh & Shiloah, 1982; Lukens, 1987; Maloney, MacFarlane, & Rimsza, 1983). Other researchers have correctly pointed out that nitrate is essential to human health. Nitrogen itself is a basic building block of protein; nitric oxide is utilized by both the neurological and immune systems to carry out vital bodily functions (Archer, 2002; Avery & Lhirondel, 2003; Billiar, Curran, Ferrarri, Williams, & Simmons, 1990; Duncan...