LONDON (AP) - New research bolsters the theory that the female hormone estrogen might protect women from colorectal cancer.

Italian scientists have found that women had about a 20 percent lower chance of developing the disease if they used oral contraceptives.

"For a while now we have suspected that estrogen in the pill could protect against bowel cancer and our research has gone some way to confirm this," said Dr. Carlo La Vecchia, who led the study. "In the future, it may be possible to develop new treatments that take advantage of the anticancer qualities of the pill."

The findings, published Monday in the British Journal of Cancer, are similar to those of a recent study which suggested that hormone replacement therapy, or HRT, could protect women from colorectal cancer to the same degree.

Over the last 20 years death rates from bowel cancer have dropped more in women than in men. Some scientists believe this could be partly due to estrogen found in oral contraceptives and hormone replacement therapy.

That theory deserves more attention, according to Dr. Michael Thun, head of epidemiology at the American Cancer Society.

"How relevant these findings are to today's pill use is unclear because they relate mostly to older formulations," said Thun, who was not involved in the research. "But this does support the hypothesis that estrogen plays a role in suppressing colorectal cancer."

The study by researchers from the Institute of Pharmacological Research in Milan, Italy, pulled together the evidence from 19 international investigations into a possible link between birth control pills and cancer of the colon and bowel. It is the first comprehensive analysis of the topic.

Nearly 1 million people were diagnosed with colorectal cancer worldwide last year, the World Health Organization estimates. The American Cancer Society projects that more than 135,000 Americans will be diagnosed with the disease this year.

Studies have shown there appear to be other anticancer benefits to the pill, but that it may also promote some types of cancer. Research suggests it may ward off ovarian and womb cancer but increase the risk of breast cancer.

"Women need to look at the balance of all the benefits and risks," said Dr. Anne Szarewski, a gynecological cancer expert at the Imperial Cancer Research Fund in London. "It'll depend on the individual profile. For someone with a family history of breast cancer, any additional risk will turn them off."

Regular screening after the age of 50, regular exercise and maintaining a healthy weight are considered the best ways to reduce the chances of developing colorectal cancer, Thun said.

The study was funded by the Italian Association for Cancer Research.

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