Several case-control studies have been performed to evaluate the potential relationship between nitrate exposure from drinking water and reproductive or developmental effects in humans. One study compared people with CNS defects to controls without such effects in New Brunswick, Canada, and found no significant association between birth defects and nitrate exposure (Arbuckle et al. 1988). A study in Boston found that exposure to nitrate in water was associated with a decrease in the risk of spontaneous abortion but that exposure to nitrite had no effect (Aschengrau et al. 1989). An increase in the risk of birth defects was reported in South Australia among women consuming groundwater containing nitrate at 5-15 mg/L, compared with women consuming rainwater containing nitrate at less than 5 mg/L (Scragg et al. 1982; Dorsch et al. 1984). The authors could not attribute their results to nitrate, however, because actual exposure to nitrate was not determined and because other contaminants of groundwater were probably present as a result of the runoff of agricultural chemicals and chemicals used in the local wood-processing industries.
Inorganic nitrite, but not inorganic nitrate, can produce hypotension in humans as a result of its action as a smooth muscle relaxer, especially in the vascular system. This effect is similar to that of some organic nitrates and is thought to result from the production of S-nitrosothiols or nitric oxide; both stimulate guanylate cyclase activity (Knowles et al. 1989). Hypotension as a result of sodium nitrite administration has been recognized for well over a century. It occurs in most, if not all, mammals, including humans,