NEW YORK (Reuters Health) - Data from a study involving nearly 40,000 women support a potential role of oral contraceptives in reducing the risk of colorectal cancer.

As lead investigator Dr. Jennifer Lin told Reuters Health, "Our study suggests that exogenous hormone use such as oral contraceptives may confer some protection among women against colorectal cancer development."

Lin of Harvard Medical School, Boston and colleagues evaluated associations of oral contraceptive use and reproductive factors and risk of colorectal cancer among 39,680 participants in the Women's Health Study. They report their findings in the April issue of the American Journal of Epidemiology.

During an average of 11 years the women were followed, 267 cases of colorectal cancer were diagnosed.

Ever having used of oral contraceptives was associated with a 33 percent lower risk of colorectal cancer, the team reports.

For OC use from 6 months to less than 3 years, the relative risk reduction was on the order of 39 percent.

There was little further decrease in risk with longer duration of OC use.

However, despite the apparent relationship with oral contraceptives, concluded Lin, "The association between endogenous production of sex hormones -- reproductive factors - and colorectal cancer incidence remains unclear."