Summary: Pregnant women who drank household water containing nitrate gave birth to infants who weighed, on average, about ten grams less than infants of mothers whose household water showed no detectable nitrate. Elevated nitrate in tap water can also cause infant methemoglobinemia, a potentially fatal condition in newborns.
Source: University of Illinois
A large population study of Danish births found a small but measurable association between maternal nitrate exposure from household drinking water and reduced newborn size. Researchers from the University of Illinois Chicago and Aarhus University reported that babies born to mothers with detectable nitrate in their household water weighed, on average, roughly 10 grams less than babies born to mothers with undetectable nitrate levels in drinking water.
Published in Environmental Health Perspectives, the study tracked prenatal exposure to nitrate in tap water and related it to newborn measurements. The research is notable because even relatively low nitrate concentrations — around half of the U.S. Environmental Protection Agency (EPA) allowable limit — were linked to small reductions in birth weight and body length.
Nitrate commonly enters drinking water supplies when fertilizers leach into groundwater and surface water sources. High concentrations of nitrate in drinking water are a known risk factor for infant methemoglobinemia, sometimes called “blue baby syndrome,” a condition in which nitrate interferes with hemoglobin’s ability to carry oxygen and can be life-threatening. To reduce this risk, the EPA has set a drinking water standard for nitrate at 10 milligrams per liter (10 mg/L). Denmark’s regulatory limits are similar to those used in other high-income countries.
To evaluate the relationship between drinking water nitrate and fetal growth, the investigators linked national water-quality monitoring records to Danish health registries. Those registries provide comprehensive, long-term data on births and health outcomes, enabling robust population-level analyses. The research team estimated maternal nitrate exposure during pregnancy for nearly one million Danish-born children born between 1991 and 2011 by matching historic nitrate measurements to residential addresses during pregnancy.
Analyses controlled for relevant maternal and demographic factors and examined multiple markers of fetal growth: birth weight, low birth weight (LBW), body length, and head circumference. Using both categorical exposure groups and continuous (log-transformed) nitrate measures, the researchers observed a consistent pattern: increasing nitrate concentrations were associated with slightly lower birth weight and shorter body length at term. No meaningful association was found between nitrate exposure and head circumference or the risk of low birth weight.
Specifically, models indicated that a maternal drinking water nitrate concentration around 25 mg/L — about half the European Union drinking water limit cited in the study — corresponded to an average reduction in term birth weight of approximately 9.7 grams compared with 0 mg/L exposure. Although these per-infant differences are small, the authors emphasize that even modest reductions in birth weight or length can be important for infants who are already at risk for growth restriction or other health challenges.
“The observed decreases in birth weight and length are modest but clinically meaningful in the context of population health,” said Vanessa Coffman, UIC visiting research specialist in the School of Public Health and the study’s lead author. “Because birthweight is a key marker of newborn health and development with lifelong implications, we need to better understand how low-level nitrate exposure contributes to fetal growth.”
Co-authors include Leslie Stayner (University of Illinois Chicago); Torben Sigsgaard, Anja Søndergaard Jensen, Betina Trabjerg, Carsten Pedersen, Jørn Olsen, Inger Schaumburg, and Jörg Schullehner (Aarhus University); Birgitte Hansen (Geological Survey of Denmark and Greenland); and Marie Pedersen (University of Copenhagen).
Funding: This research was supported by grant awards from the National Institutes of Health (R01ES02782301A1).
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Source: University of Illinois
Contact: Jackie Carey – University of Illinois
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Original Research: Open access.
“Prenatal Exposure to Nitrate from Drinking Water and Markers of Fetal Growth Restriction: A Population-Based Study of Nearly One Million Danish-Born Children” by Vanessa Coffman et al. Environmental Health Perspectives
Abstract
Prenatal Exposure to Nitrate from Drinking Water and Markers of Fetal Growth Restriction: A Population-Based Study of Nearly One Million Danish-Born Children
Background:
High concentrations of nitrate (NO3−) in drinking water are a recognized cause of methemoglobinemia in infants. However, the effects of lower, chronic prenatal exposure to nitrate on fetal growth have been less clear, with limited and inconsistent evidence to date.
Objectives:
This study aimed to determine whether maternal exposure to nitrate in drinking water during pregnancy is associated with newborn size at birth among full-term (≥37 weeks gestation) singletons in a nationwide Danish cohort.
Methods:
Maternal nitrate exposure was estimated by linking residential addresses during pregnancy to nitrate measurements in the national water monitoring database for births occurring in Denmark from 1991 to 2011. Infant outcomes (birth weight, low birth weight, body length, and head circumference) and covariates were obtained from national registries. Statistical analyses used linear and logistic regression with generalized estimating equations to account for multiple births to the same mother, and nitrate exposure was modeled both in categories and as a log-transformed continuous variable.
Results:
The authors found a statistically significant downward trend in term birth weight with increasing nitrate exposure, whether using categorical or continuous exposure measures. In continuous models, an exposure level of 25 mg/L NO3− (approximately half of some regulatory limits cited) was associated with an average birth weight reduction of about 9.7 grams compared with 0 mg/L exposure. Body length declined with higher nitrate exposures in both categorical and continuous analyses. There was little evidence linking nitrate exposure to head circumference or the incidence of low birth weight.
Discussion:
While the estimated reductions in birth weight and length are small at the individual level, they may be meaningful for population health and for infants already at risk of growth restriction. The findings suggest that even low-level prenatal nitrate exposure from drinking water could modestly affect fetal growth. The authors recommend further research in other settings and studies that also account for dietary nitrate sources to confirm these associations and better inform drinking water standards.