Summary: Pregnant women exposed to nitrates through household drinking water had, on average, babies that weighed ten grams less than women with no exposure to nitrates in drinking water. High levels of nitrate in tap water can cause infant methemoglobinemia, a fatal condition in newborns.
Source: University of Illinois
Women whose household drinking water contained nitrate had babies that weighed, on average, 10 grams less than babies born to mothers where household water had no detectible nitrate, according to a new study from researchers at the University of Illinois Chicago and Aarhus University.
The study, which is published in the journal Environmental Health Perspectives, followed pregnant women living in Denmark. The researchers found that even low nitrate levels — about half of the allowable level set by the U.S. Environmental Protection Agency, or EPA — caused an adverse effect.
“While the effects of elevated nitrate levels on infant health are known, little research has been done on the impact of lower levels of nitrate in drinking water may have on neonates,” said Vanessa Coffman, UIC visiting research specialist at the School of Public Health and lead author on the paper. “This is a critical data gap if we want to assess the adequacy of our current water standards for nitrate.”
Drinking water becomes contaminated by nitrate when fertilizers seep into drinking water sources. High levels of nitrate in tap water can cause infant methemoglobinemia — a potentially fatal condition known as blue baby syndrome in which a baby’s skin turns blue — as nitrate prevents hemoglobin in the blood from carrying oxygen. For this reason, the EPA set standards for nitrate in drinking water at 10 parts per million, to reduce the risk of blue baby syndrome. In Denmark, the allowable level of nitrate in drinking water is similar.
In the largest study of the association between nitrate in drinking water and birth weight, Coffman and colleagues estimated maternal nitrate exposure for 852,348 live births in Denmark from 1991 to 2011. They linked home addresses with nitrate data from a national water quality monitoring database with data from Danish registries on infant birth weight, length and head circumference — these registries offer an unparalleled resource for epidemiologists, as they are some of the most complete in the world, with national health care data and robust individual demographics and environmental data spanning decades.
The researchers found that levels of nitrate in maternal drinking water were associated with birth weight, but the weight differences were small but important. Babies born to mothers whose drinking water was estimated to contain about half of the allowable level of nitrates were on average 10 grams lighter than babies born to households where drinking water nitrate levels were undetectable. The researchers also observed a decrease in body length with increasing nitrate concentrations in drinking water. No effect was observed on head circumference.
“This difference in weight and body length is small but could have an impact on health if the baby is underweight to begin with for other reasons. Birthweight is a critical marker for health, as it can have a life-long impact on health and development,” Coffman said.
Leslie Stayner of UIC; Dr. Torben Sigsgaard, Anja Søndergaard Jensen, Betina Trabjerg, Carsten Pedersen, Dr. Jørn Olsen, Dr. Inger Schaumburg and Jörg Schullehner of Aarhus University in Denmark; Birgitte Hansen of the Geological Survey of Denmark and Greenland; and Marie Pedersen of the University of Copenhagen are co-authors on the paper.
Funding: This work was supported by grant awards from the National Institutes of Health (R01ES02782301A1).
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Prenatal Exposure to Nitrate from Drinking Water and Markers of Fetal Growth Restriction: A Population-Based Study of Nearly One Million Danish-Born Children
High levels of nitrate (NO−3NO3−) in drinking water cause methemoglobinemia in infants; however, few studies have examined the potential effects of low-level exposure on fetal growth, and the results have been inconsistent.
We sought to assess the association between maternal exposure to nitrate in drinking water during pregnancy and offspring size at birth in a nationwide study of full-term (≥37 wk≥37 wk gestation) live-born singletons.
We estimated maternal nitrate exposure for 898,206 births in Denmark during 1991–2011 by linkage of individual home address(es) with nitrate data from the national monitoring database. Maternal address during pregnancy, infant size at birth [i.e., birth weight, low birth weight (LBW), body length, and birth head circumference] and covariates were compiled from the Danish Civil Registration System, the Danish Medical Birth Register, and The Integrated Database for Longitudinal Labor Market Research. Linear and logistic models with generalized estimating equations were used to account for multiple births to an individual. Nitrate exposure was modeled using five categories and as a log-transformed continuous variable.
There was evidence of a decreasing trend in models for term birth weight using categorical or continuous measures of exposure. Modeling exposure continuously, a difference of −9.71 g−9.71 g (95% confidence interval: −14.60−14.60, −4.81−4.81) was predicted at 25 mg/L25 mg/L(half the value of the European Union drinking water standard) compared with 0 mg/L NO−30 mg/L NO3−. Body length also decreased as nitrate concentrations increased in categorical and continuous models. There was little evidence of an association between NO−3NO3− and head circumference or LBW.
Although the estimated effects were small, our findings for live singleton births to Danish-born parents suggest that maternal intake of nitrate from drinking water may reduce term birth weight and length, which are markers of intrauterine growth. However, there was little evidence for an association between nitrate and head circumference or LBW. Future studies in other populations and with data on dietary sources of nitrate are encouraged to confirm or refute these findings.