Long-term cancer and overall mortality associated with drinking water nitrate in the United States

Objectives: Nitrate is a probable carcinogen regulated in drinking water by the US Environmental Protection Agency (EPA) to a maximum contaminant level (MCL) of 10 mg/L nitrate -nitrogen (NO3-N; equivalent to 44.3 mg/L NO3). We aimed to determine the association of US drinking water nitrate levels with overall as well as cardiovascular, cancer, and other cause mortality. Study design: This study used a population-based retrospective cohort design. Methods: We analyzed data from 2029 participants of the 2005-2006 National Health and Nutrition Examination Survey followed for mortality until 2019 for a median of 13.9 years. We used Cox proportional hazards regression to estimate the hazard ratio (HR) and 95% confidence interval (CI) for mortality associated with drinking water nitrate, adjusting for covariates that included socio-economic factors and pack-years of cigarette smoking. Results: Drinking water nitrate was detected in 50.8 % of the samples, had a median concentration of 0.77 mg/L NO3, and was above US EPA MCL in 0.4 % of participants. In adjusted analysis, drinking water nitrate detection was associated with 73 % higher cancer mortality (HR: 1.73, 95% CI: 1.19-2.51), whereas a 10 -fold increase in drinking water nitrate levels was associated with 69 % higher cancer mortality (HR: 1.69, 95% CI: 1.24-2.31) and 21 % higher overall mortality (HR: 1.21, 95% CI: 1.00-1.46). Drinking water nitrate below EPA MCL was still associated with higher cancer mortality (HR: 1.61, 95% CI: 1.07-2.43 per 10 -fold increase and HR: 1.61, 95% CI: 1.08-2.42 for detection). Conclusions: Levels of drinking water nitrate may be an overlooked contributor to cancer mortality in the United States. (c) 2024 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.