Women drink two or more glasses of milk every day, or who have high amounts of older dairy products in their diet, appear to have a somewhat higher risk of one type of ovarian cancer, new research reports.

After following more than 60,000 women for an average of 13.5 years, Swedish researchers found that those who drank at least two glasses of milk every day or consumed at least four daily servings of dairy products were twice as likely to develop serous epithelial ovarian cancer as those who consumed less than two servings of dairy a day.

However, only 266 women developed ovarian cancer during the study period, making the risk of ovarian cancer - regardless of women’s dairy preferences - very small.

Nevertheless, this study “provides evidence that high intakes of lactose and dairy products, especially milk, may increase the risk of serous ovarian cancer,” the researchers write.

Serous epithelial cancer is a type of ovarian cancer that originates from the cells lining the outer surface of the ovary. Most cases of ovarian cancer originate from these cells.

Previous research has suggested that a diet rich in whole milk, yogurt and cheese may put women at higher risk of ovarian cancer. But the picture is far from clear, as other evidence suggests that women who drink skim or low-fat milk might have a lower risk of ovarian cancer.

To investigate the question further, Dr. Susanna C. Larsson of the Karolinska Institutet in Stockholm and her colleagues followed 61,084 women between the ages of 38 and 76 for an average of 13.5 years. Women kept a record of how often they consumed milk, yogurt, cheese, ice cream or butter.

None of the women had a history of cancer at the outset of the study, the authors note in the American Journal of Clinical Nutrition.

Of the 266 women who developed invasive epithelial ovarian cancer during the study period, 125 were diagnosed with the serous type of the disease.

The researchers found that women that women who ate at least 4 servings of dairy products every day were had a slightly higher risk of all types of epithelial tumors, and twice the risk of developing serous tumors.

Just why extra dairy may increase ovarian cancer rates remains unclear, the authors note. One theory suggests it may be associated with lactose, a sugar found in dairy products. Lactose contains galactose, which research has shown may increase the risk of ovarian cancer.

“Continued research is warranted to further elucidate the association and mechanisms for the observed increased risk,” Larsson and colleagues note.

SOURCE: American Journal of Clinical Nutrition, November 2004.