A 20-year study of nearly 11,000 Bangladeshi adults found that reducing arsenic levels in drinking water over time cut deaths from heart disease, cancer and other chronic conditions by half. The work was published in JAMA.
Researchers from Columbia University, Mailman School of Public Health and New York University studied one of the most common global health problems. The naturally occurring presence of arsenic in groundwater remains a serious threat worldwide. In the United States, more than 100 million people rely on underground sources, including private wells, where arsenic levels can be elevated. Arsenic is one of the most common chemical contaminants in drinking water today.
Participants whose urinary arsenic levels dropped from high to low had about the same mortality rate as people who had only low levels of arsenic exposure all along. The more arsenic concentrations fell, the more markedly the risk of death decreased. In contrast, those who continued to drink high-arsenic water did not experience a reduction in chronic disease mortality. Arsenic is naturally present in groundwater and has no taste or odor, so people can drink contaminated water for years without noticing. An estimated 50 million people in Bangladesh drank water containing arsenic levels above the World Health Organization’s limit of 10 micrograms per liter. WHO described this situation as the largest case of mass chemical poisoning in history.
As the study progressed, participants were regularly tested in their urine to determine arsenic concentrations—a reliable indicator of internal exposure—and the causes of death were recorded. This detailed collection of data made it possible to compare the long-term outcomes of people who were able to reduce their arsenic exposure with those who continued to be exposed to high levels. Throughout the study, state and local initiatives labeled wells as safe or hazardous based on their arsenic levels. As a result, many families switched to cleaner sources or drilled new wells, while some of the population continued to use contaminated water. This natural partition allowed scientists to clearly evaluate the impact of reducing arsenic exposure.
Over the years of observation, the level of water contamination with arsenic has noticeably decreased. In public wells, concentrations fell by about 70% as more households chose safer sources. Urine tests showed a similar, averaging 50%, reduction in internal exposure, which persisted through 2022.