Prenatal nitrate and nitrite intake in mammals: A scoping review of effects and associations with pregnancy and maternal and child health

Nitrate and nitrite are present in drinking water, vegetables and processed meats. While they may offer health benefits in some contexts, high levels, especially during pregnancy, can be harmful. This scoping review investigates prenatal nitrate/nitrite exposure and maternal, child, pregnancy and birth outcomes, in animal models and humans. Six databases were searched systematically for peer-reviewed publications relating to nitrate and/or nitrite exposure in pregnancy. 3834 unique papers were identified, with 133 meeting inclusion criteria. In human studies (n = 66), high processed meat nitrite exposure was associated with congenital anomalies and childhood cancer, although primarily in conjunction with nitrosatable medication exposure. Fresh vegetable sources of nitrate/nitrite were associated with neutral or positive health outcomes. Prenatal drinking water nitrate exposure was moderately associated with preterm birth, while evidence for congenital anomalies, growth restriction, preeclampsia and early puberty was limited or inconsistent. Associations appeared at concentrations as low as 5 % of the WHO drinking water guideline. However, other water contaminants and exposures such as nitrosatable medications were only addressed in a minority of studies. Animal studies (n = 67) reported effects of nitrate/nitrite exposure on mortality and birthweights through pathways involving methemoglobinemia, inflammation, DNA-damage and endocrine disruption, however, dosing was often extreme. While vegetable sources of nitrate/nitrite show some health benefits, exposure to meat and drinking water sources should be limited, although safe limits and causal evidence are not fully established. Public health policy should prioritise decreasing nitrate exposure within the context of broader water quality concerns and barriers to perinatal health.