Researchers from the University of California (UC) Berkeley and the Pontifical Catholic University of Chile have linked arsenic to a 50 percent drop in breast cancer deaths.

The researchers looked at the results of breast cancer mortality data from a region in Chile where residents were inadvertently exposed to high levels of arsenic, a naturally occurring element found in many minerals. Instead of an increase in mortality, as with many other cancer sites, the study found that breast cancer deaths were cut in half during the period that coincided with high arsenic exposure. The effect was more pronounced among women under age 60, with mortality in these women reduced by 70 percent.

"What we found was astonishing. We have 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," said study lead author Dr Allan Smith, UC Berkeley professor of epidemiology and director of the Arsenic Health Effects Research Program.

The research is published in the journal EBioMedicine.