Reducing arsenic in drinking water cuts risk of death, even after years of chronic exposure

A new 20-year study of nearly 11,000 adults in Bangladesh found that lowering arsenic levels in drinking water was associated with up to a 50 percent lower risk of death from heart disease, cancer and other chronic illnesses, compared with continued exposure.

Published today in the Journal of the American Medical Association, the study provides the first long-term, individual-level evidence that reducing arsenic exposure may lower mortality, even among people exposed to the toxic contaminant for years.

The landmark analysis, led by researchers at Columbia University and New York University, is important for public health because groundwater contamination from naturally occurring arsenic remains a serious issue worldwide. In the United States, more than 100 million people rely on potentially contaminated groundwater sources, especially private wells, for their drinking water. Arsenic is among the most common chemical pollutants.

“We show what happens when people who are chronically exposed to arsenic are no longer exposed,” said co-lead author Lex van Geen of the Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School. “You’re not just preventing deaths from future exposure, but also from past exposure.”

The results provide the clearest evidence to date of the link between arsenic reduction and lower mortality, says co-lead author Fen Wu of NYU Grossman School of Medicine. For two decades, the research team followed each participant's health and repeatedly collected urine samples to track exposure, which they say strengthened the accuracy of their findings.

People whose urinary arsenic levels dropped from high to low had mortality rates identical to those who had consistently low exposure throughout the duration of the study. The larger the drop in arsenic levels, the greater the decrease in mortality risk. By contrast, individuals who continued drinking high-arsenic water saw no reduction in their risk of death from chronic disease.

Arsenic is a naturally occurring element that accumulates in groundwater, and because it has no taste or odor, people can unknowingly drink contaminated water for years. In Bangladesh, an estimated 50 million people have been exposed to drinking water with levels above the World Health Organization’s guideline of 10 micrograms per liter. The WHO has called it the largest mass poisoning in history.

Tracking exposure and mortality

From 2000 to 2022, the Health Effects of Arsenic Longitudinal Study (HEALS) tracked thousands of adults and tested more than 10,000 wells in Araihazar, Bangladesh, where many people rely on shallow tube wells with arsenic concentrations ranging from negligible to extremely high.

Researchers periodically measured arsenic levels in participants’ urine—a marker of ingested arsenic and a proxy for internal exposure—and recorded causes of death. These individual-level data allowed the scientists to compare health outcomes between those who reduced their exposure and those who remained highly exposed.

Throughout the project, national and community programs tested wells in Araihazar for arsenic and labeled them as safe or unsafe, prompting many households to switch to or install safer wells. Others continued using contaminated wells, creating a natural comparison group within the study.

Arsenic exposure dropped significantly in Araihazar over the study period. The average concentration in the wells people relied on fell by about 70 percent because many households switched to safer water sources. Urine tests confirmed the change: participants’ internal arsenic exposure declined by about 50 percent, on average, and remained lower through 2022.

These patterns held even after adjusting for differences in age, smoking, and socioeconomic status. Participants whose exposure remained high, or increased over time, continued to face significantly higher risks of death from chronic diseases.

Van Geen likened the impact of reducing arsenic exposure to quitting smoking: the health risks do not disappear immediately but decline steadily over time.

The findings highlight the importance of ensuring access to arsenic-free drinking water. In Bangladesh, measures such as testing well water, labeling unsafe water sources, drilling private wells and deeper government wells have already delivered measurable improvements for many people.

“Our findings can now help persuade policymakers in Bangladesh and other countries to take emergency action in arsenic ‘hot spots’,” says co-author Kazi Matin Ahmed of the University of Dhaka.

To expand access to safe water, the research team is working with the Bangladeshi government to make well data more accessible. They’re piloting NOLKUP (“tubewell” in Bangla), a free app developed from more than six million well tests. Users can search for specific wells, check arsenic levels and depths, and locate nearby safer sources. The app also helps planners identify communities most in need of new, deeper wells.

By showing that health risks decline even for those already exposed to arsenic, the study highlights a critical opportunity: investing in clean water can save lives within a generation.

“This finding is deeply rewarding. Public health is often the ultimate example of delayed gratification,” says Joseph Graziano, Professor Emeritus at Columbia University’s Mailman School of Public Health and a principal investigator of the decades-long research.

The study team comprised researchers from the New York University Grossman School of Medicine; Lamont-Doherty Earth Observatory and the Mailman School of Public Health at Columbia University; Boston University School of Public Health; Department of Geology, University of Dhaka; and the Institute for Population and Precision Health, University of Chicago.

The HEALS study was launched by Columbia University through the National Institute of Environmental Health Sciences’ Superfund Research Program, with most U.S. collaborators based at Columbia when the project began.