Arsenic in Drinking Water Linked to a 50% Drop in Breast Cancer Deaths

Arsenic is widely recognized as a deadly toxin, responsible for severe health risks when found in drinking water.

But what if this notorious poison could also be a lifesaver?

A groundbreaking study has revealed an unexpected link: exposure to high levels of arsenic in drinking water was associated with a 50% reduction in breast cancer deaths in one region of Chile.

For decades, arsenic contamination has been a pressing public health issue in countries like China, Bangladesh, and Chile.

Long-term exposure is linked to various cancers, including lung and bladder cancer, making this new finding all the more shocking.

Could it be possible that arsenic, long feared for its toxic effects, might also have medicinal potential?

The Accidental Experiment in Chile

Between 1958 and 1970, the residents of Antofagasta, a city in northern Chile, were unknowingly part of a large-scale natural experiment.

Their drinking water, sourced from geothermal wells in the Andes Mountains, contained alarmingly high levels of arsenic—more than 800 micrograms per liter, 80 times higher than the safe limit set by the World Health Organization (WHO).

As expected, this contamination led to an increase in deaths from multiple cancers. However, one anomaly stood out: breast cancer deaths dropped dramatically.

Overall breast cancer mortality in Antofagasta was 50% lower than in the rest of Chile during the exposure period.
For women under 60, the decline was even more drastic—70% lower than the national average between 1965 and 1970.

Dr. Allan Smith, an epidemiologist from the University of California, Berkeley, and lead researcher of the study, expressed his astonishment at the findings:

“We’ve been studying the long-term effects of arsenic in this population for many years, focusing on increased disease and mortality attributed to the historical exposure to arsenic in this population. But what we found regarding breast cancer was astonishing.”

Can a Poison Be a Cure?

This discovery challenges a fundamental belief about arsenic—that it is purely harmful. In fact, arsenic-based treatments have been used in medicine before.

In 2000, the U.S. Food and Drug Administration (FDA) approved arsenic trioxide as an effective treatment for acute promyelocytic leukemia, a rare blood cancer.

The Chilean study suggests that arsenic exposure might have had a similar effect on breast cancer cells.

To investigate, researchers grew human breast cells and breast cancer cells in the lab, exposing them to arsenic.

The results were striking:

The arsenic killed breast cancer cells while sparing normal breast cells, which seemed to be more resistant to the toxin than other tissue types.
This selective toxicity suggests arsenic might hold potential as a breast cancer treatment.

But how does arsenic target cancer cells?

Scientists speculate it could be linked to the way arsenic disrupts cellular metabolism, forcing cancer cells—already under metabolic stress—to die, while healthy cells are better equipped to survive.

Clinical Trials and Cautious Optimism

While these findings are fascinating, they don’t mean that arsenic should be considered a breast cancer treatment just yet.

The researchers are now working on designing clinical trials to see if arsenic can be safely and effectively used in a controlled medical setting to treat advanced breast cancer.

Dr. Smith emphasized the importance of further research:

“We do not know if the treatment will work, but carefully designed clinical trials should take place as soon as possible based on this new evidence.”

If these trials confirm arsenic’s cancer-fighting properties, it could revolutionize breast cancer treatment, offering a new weapon against the disease—one derived from a substance long considered an enemy of human health.