One day after women were advised that caffeine could endanger their pregnancy comes a new study that suggests that the substance may actually lower their ovarian cancer risk.

The study, to be published in the American Cancer Society journal Cancer, finds that caffeine seems to lower a woman's ovarian cancer risk, while smoking and drinking do not seem to affect it.

The link between caffeine and lower ovarian cancer risk was even stronger in women who had never used oral contraceptives or postmenopausal hormone therapy.

Dr. Shelley S. Tworoger, of Harvard Medical School and the Harvard School of Public Health, made the discovery after examining data from the ongoing Nurses' Health Study -- which began in 1976 and includes 121,701 U.S. female registered nurses. The nurses in the study completed questionnaires every two years to update researchers on their lifestyles and to report any newly diagnosed diseases.

Tworoger and her co-investigators looked at the link between smoking and ovarian cancer risk, and between alcohol or caffeine and ovarian cancer risk among the women between June 1976 and June 2004.

They could find no link between alcohol consumption and ovarian cancer risk.

Nor could they find any link between current or past smoking and ovarian cancer risk. However, the more and the longer the smokers kept up the habit, the higher their risk for mucinous tumors, a rare form of ovarian cancer.

The researchers did find a lowered risk of ovarian cancer in the women who said they drank caffeinated coffee; the link disappeared among women who said they regularly drank decaf.

The reduction in risk with higher caffeine intake appeared to be strongest for women who had never used oral contraceptives or postmenopausal hormones.

The authors say they don't know why caffeine would lower ovarian cancer risk but they say the possibility that it could "is intriguing and warrants further study."