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Global health research connects nitrate in drinking water with birth defects

Birth defects are a leading cause of infant mortality and may be associated with substantial morbidity and long-term disability.  New findings from an epidemiologic study conducted by researchers at the University of Illinois, School of Public Health and Aarhus University in Denmark provide some evidence that prenatal exposure to nitrate in drinking water, one of the most frequently detected contaminants in water systems around the world, may increase the risk of birth defects.

The study is published in the journal Lancet Regional Health Europe, with Leslie Stayner, PhD, professor emeritus of epidemiology at the University of Illinois Chicago School of Public Health, as the lead author, and Torben Sisgaard, PhD, from Aarhus University as the senior author.

“Our findings, along with evidence of other adverse birth outcomes associated with prenatal exposure to nitrate in drinking water, raise serious concerns about the adequacy of current drinking water standards for protecting children,” Stayner said.

Examining a cohort of more than one million births in Denmark, researchers found strong evidence that nitrate exposure may increase the risk of birth defects of the eye.  The study findings also suggest nitrate may increase the risk of ear, face, neck and nervous system birth defects among children with mothers younger than 25.  Nitrate levels in this study were generally below both European Union and U.S. limits. The findings of the study were largely unchanged when the analyses were restricted to mothers who had not been exposed to nitrate concentrations that were in excess of the current standards.

The investigators are not exactly sure why maternal age would play a key role in nitrate exposure-caused birth defects.  Theories include the propensity of young women to reside in larger cities and thereby be co-exposed to ambient air pollution and other urban stressors.  Among the Danish cohort of mothers, young mothers may be more likely to smoke and engage in other unhealthy behaviors, as compared with women of older ages that more likely to have planned to become pregnant. Finally, young mothers may be less likely to take folate (a powerful anti-oxidant) before and during pregnancy.

The research was conducted in Denmark because of the nation’s availability of records from its national health care system and extensive nitrate in water monitoring data. Nitrate concentrations in 130,944 drinking water samples from 3,907 public waterworks were calculated and used to estimate nitrate concentrations at the household level. These estimates could then be linked with information from a national address database to estimate maternal exposures during pregnancy. Linking birth defects data with nitrate exposures at the individual level during pregnancy for such a large sample population would be very difficult in other countries Worldwide.

“These findings are particularly troubling for areas of the world with intense agriculture and higher exposures to nitrate in drinking water than in Demark, like areas in our Midwestern states,” Stayner said.  “Further studies are clearly warranted.”

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