Recent studies highlight the detrimental effects of chronic exposure to high nitrate levels in drinking water on pregnancy outcomes. However, the mechanisms, safety thresholds for pregnant health, and the influence of source on safety are unclear. This scoping review therefore aims to examine all literature on the effects of prenatal nitrate and nitrite intake, both positive and negative, on maternal and neonatal health outcomes, in both humans and non-human mammals.
Six databases, Medline, Embase, CINAHL, SPORTDiscus, Web of Science and Global Health, were searched for publications regarding exposure to nitrate or nitrite during pregnancy. Covidence was used for dual reviewer screening and extraction, and non-English papers were translated using Google Translate.
Our search found 3462 potentially relevant unique papers, with 129 papers meeting inclusion criteria. Publication date ranged from 1959 to 2024, with 13% of studies published in a language other than English. Nitrate and nitrite sources included drinking water (53%), processed meats (10%), vegetables (14%), and direct administration (24%). Animal studies (n=64, 49.6%) included rodents (74%), ruminants (18%) pigs (6%), and horses (1.5%), exposed to nitrate (44%) and/or nitrite (56%). While 78% found a negative health effect of nitrate/nitrite, the 5% of studies that used concentrations relevant to human exposure levels found none or a positive effect. Human studies (n=65, 50.3%) examined outcomes including congenital anomalies (25%), postnatal cancers (18%), birthweight (15%), gestational length (13%), postnatal diabetes (4%), spontaneous abortion (4%), maternal cardiovascular health (4%), and other (16%), with 72% finding some association of change in health outcomes with nitrate, but only 46% showing clearly negative health associations.
This review reveals gaps in current literature and shows that nitrate/nitrite source and concentration complexly influence health outcomes in pregnancy through poorly understood mechanisms. Additionally, we demonstrate that excluding non-English papers is unnecessary with powerful translation tools freely available.