Are current drinking water standards for nitrate sufficient for preventing adverse birth outcomes and childhood cancer– Findings from a cohort of over one million children in Denmark

Background and Aims: Current standards for nitrate in drinking water in EU and the US are based on preventing methemoglobinemia a condition that occurs at high levels of exposure. There is growing evidence that exposure to nitrate in water is associated with adverse birth outcomes. Our aim is to summarize the findings from our nationwide studies of the population exposed to levels below the current standards in Denmark. Methods: We studied a cohort of all singletons liveborn to Danish-born parents from 1991–2013 (N=1,018,914). Data on birth weight, head circumference, body length, gestational age, birth defects and childhood cancer were obtained from Danish registers. Nitrate levels were estimated at the individual residential level. The analyses presented here were restricted to women who had pregnancy average exposures during their pregnancy that were lower than the current EU limit (50 mg/L N03). Results: Prenatal exposure to nitrate was found to be significantly associated with a decrease in birth weight (p<0.001), body length (p<0.01), and increased risk of small-weight-for-gestational age (p=0.002), all markers of fetal growth restriction. However, we did not observe evidence of an effect on head circumference or term low birth weight. Significant evidence of an exposure-response relationship was also observed for preterm births (p<0.04), eye cataracts (p=0.004), and for nervous system (p=0.003) and ear, face and neck (p=0.01) birth defects among women <25 years of age. A trend was not observed for childhood cancers, but a significant increase in central nervous system cancers was observed for the highest exposure group (>25 mg/L) with which was strongest for the preconception period (OR=1.82, 95%CI:1.09 to 3.04). Conclusions: Our findings along with the results from other recent studies suggest that nitrate exposure from drinking water is associated with adverse birth outcomes and childhood CNS cancers at currently allowable levels. Key Words: nitrate, birth outcomes