A diet high in olive oil may lower a woman's risk of developing ovarian cancer, according to a study reported in the journal Cancer Causes and Control (Vol. 13: 465-470).

The study found that women whose diet included large amounts of olive oil reduced their risk of ovarian cancer by 30%.

The "Mediterranean" diet, in which olive oil plays a major role, has long been hailed as the ideal diet for staying healthy. This health effect was mainly linked with less coronary artery disease. But many researchers have wondered if this diet also protects against cancer.

Women in the Mediterranean countries of Italy, Greece, and Spain have lower rates of ovarian cancer than do women in most other European countries. The reason for the low ovarian cancer rate has not been clear.

To learn whether diet plays a role in these lower ovarian cancer rates, the Italian researchers, led by Cristina Bosetti, ScD, of the Istituto di Ricerche Farmacologiche Mario Negri in Milan, Italy, studied the dietary habits of Italian women.

Bosetti and her colleagues questioned 1,031 women with ovarian cancer and compared their diets to those of 2,411 women without cancer.

In both groups, the women's ages were the same, as were their education levels; menopausal status; number of children; and their use of oral contraceptives. All of these factors, particularly oral contraceptives, might affect ovarian cancer rates. Studies have shown that oral contraceptives reduce ovarian cancer rates.

But, there were differences in diet. Some women took in as much as three-fourths of an ounce of olive oil daily while others consumed almost none. The women who had the highest intake of olive oil had the lowest ovarian cancer rate.

The researchers also found that high intakes of seed oils (peanut, soy, sunflower) also led to lower ovarian cancer rates.

These oils reduced the ovarian cancer rate regardless of how much butter or margarine the women ate. This suggested to the researchers that the olive oil and seed oils were protecting against the cancer.

The researchers said their results are not definitive. They suggested that women in these countries might be lowering their risk of ovarian cancer by eating these "healthy" oils.