A new long-term study offers some of the strongest evidence yet that lowering arsenic in drinking water can reduce the risk of death from chronic diseases, even for people who have been exposed for years.
The research, published in JAMA, followed nearly 11,000 adults in Bangladesh for more than two decades and found that people who reduced their exposure had a dramatically lower risk of dying from heart disease, cancer and other illnesses compared with those who continued drinking contaminated water.
Arsenic occurs naturally in groundwater and has no taste or smell, making it difficult for people to know when their wells are unsafe. In Bangladesh, an estimated 50% of the population has been exposed to levels above global safety guidelines. But the issue extends far beyond South Asia. In the United States, more than 100 million people rely on private wells or groundwater sources where arsenic can also be present.
“We show what happens when people who are chronically exposed to arsenic are no longer exposed,” said co-lead author Lex van Geen of Columbia University’s Lamont-Doherty Earth Observatory. “You’re not just preventing deaths from future exposure, but also from past exposure.”
The study used repeated urine tests to track each participant’s arsenic exposure over time and recorded causes of death for more than 20 years. People whose exposure dropped from high to low had mortality rates similar to those who had low exposure from the start. By contrast, people who continued drinking high-arsenic water saw no reduction in risk.
“Seeing that our work helped sharply reduce deaths from cancer and heart disease, I realized the impact reaches far beyond our study,” said Joseph Graziano, professor emeritus at Columbia Mailman School of Public Health. “More than two decades later, this finding is deeply rewarding.”
During the study, community programs tested wells and labeled them as safe or unsafe, prompting many households to switch to lower-arsenic sources. On average, well concentrations fell by about 70%, and participants’ internal exposure dropped by roughly 50%.
Researchers compared these changes with long-term health outcomes and found a clear pattern: The more exposure fell, the more mortality risk declined, even after accounting for differences in age, smoking and socioeconomic status.
The team likened the impact of reducing arsenic exposure to quitting smoking. Health risks can decline steadily over time, even after years of harm.
The findings highlight an important opportunity for global and domestic public health efforts. In Bangladesh, researchers have developed a free app, NOLKUP, that lets users search well data and find safer water sources. In the United States, experts recommend regular testing of private wells, since they are not regulated under federal drinking water standards.
The study underscores that lowering arsenic exposure is not only preventive but may also help people who have already faced years of contamination.
This study was supported by the National Institute of Environmental Health Sciences and collaborating U.S. and international partners.