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Testosterone increases a person's risk of developing cancer, according to a new study.

Past studies suggest that women are less likely than men to develop non-sex specific cancer of he colon, pancreas and stomach because female hormones like estrogen protect women against cancer.

However, new research from the University of Missouri shows that the male hormone testosterone increases men's risk of developing colon cancer tumors.

Lead researcher James Amos-Landgraf, an assistant professor of veterinary pathobiology in the MU College of Veterinary Medicine, examined a group of healthy male rats with normal testosterone levels.

After removing testosterone from the male rats, researchers found that colon cancer rates decreased dramatically. However, the reintroduction of testosterone brought the risk of colon cancer back up to normal.

"Previously, scientists believed that female hormones may have lent some sort of protection against tumor susceptibility," Amos-Landgraf said in a news release. "However, by showing that removing testosterone from rats leads to a drastic decrease in colon cancer susceptibility, it appears that male hormones may actually contribute to colon tumor growth rather than female hormones being protective."

Previous studies also revealed that post-menopausal women were more likely to develop colon cancer.

"All women have some level of testosterone in their bodies naturally, but those levels typically are much lower than estrogen and other female hormones," Amos-Landgraf said. "Once women experience menopause and their female hormone levels decrease, their testosterone levels become relatively higher. This corresponds to the time when they begin to experience higher rates of colon cancer and could be a sign of a relationship between testosterone levels and colon tumor growth."

The findings are published in the journal Proceedings of the National Academy of Sciences.