Two or More Daily Glasses of Milk May Raise Ovarian Cancer Risks

May 5, 2000 (Boston) -- A milk mustache may not be the most appropriate fashion statement for women concerned about their health, say scientists from Harvard Medical School. The latest finding from an ongoing study of more than 80,000 nurses suggests that women who drink two or more glasses of milk a day have a 44% higher risk of getting ovarian cancer than women who rarely drink milk.

Switching to low-fat or skim milk may not help, says Kathleen M. Fairfield, MD. Most of the milk drinkers in the nurses' study drank skim or low-fat milk. While chugging milk increases the overall risk of getting any type of ovarian cancer by 44%, it increases the risk for the most common type of ovarian cancer -- called serous tumors -- by 66%, Fairfield says. Ovarian cancer, she says, is the fifth most common cancer among American women.

Fairfield suggests that neither the fat nor the calcium content of milk increases the risk. Lactose, or milk sugar, appears to be the most likely culprit. Every 8-ounce glass of milk -- any type of milk--- contains about 11 grams of lactose.

In the body, lactose is broken down into two simple sugars -- glucose and galactose. In this case, Fairfield says that she and her colleagues think it may be the galactose that is in some way linked to cancer growth. That means lactose-free milk wouldn't be a good substitute because it contains galactose, she says.

Currently, women are advised to increase their consumption of dairy products to protect against osteoporosis, and Fairfield says those "osteoporosis recommendations are at just about the same consumption level that we are associating with ovarian cancer." What's a woman to do?

Because these results have not yet been reviewed by other scientists or published, Fairfield tells WebMD she is reluctant to make any recommendations. When asked by another physician how she would advise a 45-year-old female patient, Fairfield says she won't tell women who drink milk to stop. "But if a woman is concerned about osteoporosis but isn't currently a milk drinker, I am going to start her on calcium supplements."

The study involves 80,326 married nurses living in 11 states. When the nurses entered the study in 1976, they ranged in age from 30 to 55. Beginning in 1980, all participants were given detailed dietary questionnaires. Fairfield and her co-authors reported on 16 years of dietary studies. The women were asked about dairy product consumption and other sources of calcium.

"There were 301 cases of ovarian cancer diagnosed during the study period; 174 were serous tumors," she says.

"We found that women were getting 57% of their dietary lactose from low-fat or skim milk, 15% from whole milk, and 8% from yogurt," she says. Fairfield says cheese doesn't contain high amounts of lactose. And "whole milk accounts for only 15% of lactose because so little whole milk is consumed."

Asked if countries with a high consumption of dairy products have higher ovarian cancer rates, Fairfield says "they do, and the reverse is true as well: Low consumption of dairy products correlates to low rates of ovarian cancer."

This report, discussed at a meeting of the Society of General Internal Medicine here, follows another one last month by a different team of Harvard researchers who have been studying physicians. Scientists from the Physician's Health Study said that men who consumed more than 2.5 servings of dairy products daily had a slight increase in risk of prostate cancer. That study was presented by June M. Chan, ScD, a colleague of Fairfield.

Asked by WebMD about the common theme, Fairfield says: "It is true that there seems to be something happening with dairy products, but that study suggests a role for calcium. That is not our finding with ovarian cancer."

  • New research shows that women who drink two or more glasses of milk per day may have an increased risk of developing ovarian cancer.
  • Researchers suggest it's not the fat or the calcium, but the lactose, which breaks down in the body into glucose and galactose, that may be responsible for the increased risk.
  • It is not clear how these study results will affect dietary recommendations, as women are now advised to consume dairy products to prevent osteoporosis.