That's the claim of a Dartmouth Medical School study in the April issue of the International Journal of Cancer.
The researchers found exposure to small quantities of arsenic in drinking water may inhibit expression of genes that let cells repair damaged DNA. This DNA repair is a major biological defense the body uses to fight cancer.
This is the first study to find reduced expression of DNA repair genes in cells taken from people exposed to arsenic through their surroundings.
The study included people exposed to arsenic through their well water. People in many areas of the world consume small amounts of arsenic every day in their drinking water. This exposure to arsenic has been linked to several forms of cancer.
The researchers found an association between arsenic exposure and the expression of certain DNA repair genes. People exposed to higher levels of arsenic had several significant DNA repair genes that were expressed at lower levels than in people not exposed to arsenic.
The genes affected in the people exposed to arsenic are genes involved in nucleotide excision repair. These genes normally code for proteins that unwind DNA, cut out damaged DNA parts, seal the repaired DNA back together, and help determine which cells can't be repaired and must die.
"We were primarily interested in uncovering the mechanism to explain how arsenic causes cancer. This study supports the hypothesis that arsenic may act as a co-carcinogen -- not directly causing cancer, but allowing other substances, such as cigarette smoke or ultraviolet light -- to cause mutations in DNA more effectively," lead author Dr. Angeline Andrew says in a news release.
She says this was a small study and a larger study is needed to verify the findings.
Here's where you can learn more about arsenic and human health.