A review and analysis of 21 previous studies, published in the August 5 online issue of the International Journal of Cancer and available via Wiley InterScience at http://www.interscience.wiley.com/journal/ijc, suggests high intakes of whole milk or milk products and lactose may be associated with an increased risk of developing ovarian cancer.
Since this link was first suggested in 1989, many studies have explored the theory. To date, however, no definitive conclusions have been reached by any one of those studies.
The approach taken by the current research led by Susanna C. Larsson of the National Institute of Environmental Medicine at the Karolinska Institute in Sweden was to conduct a broad meta-analysis of relevant case-control and cohort studies.
Eighteen case-control studies of patients with ovarian cancer, as compared with healthy women, found no evidence of an association between dairy food and lactose intake and ovarian cancer, except for whole milk. Women with high whole milk consumption were found to have a 27% higher risk of developing ovarian cancer.
Prospective cohort studies, however, indicated that high intakes of milk may increase the risk of ovarian cancer. They revealed a 13% increase in ovarian cancer risk with a daily increase of 10 grams of lactose, the equivalent of one glass of milk.
When case-control and cohort studies were considered in combination, yogurt consumption was associated with a non-significant increase in cancer risk, while cheese was not associated with risk.
The disparities between case-control studies and those of cohort studies could be explained by a number of factors: selection bias, recall bias, or changes in dietary practices after cancer diagnosis.
It is not known why an increase in dairy product consumption impacts the risk for ovarian cancer. Perhaps it is because lactose produces galactose and glucose, and galactose has been thought to increase the risk by direct toxicity to the ovarian germ cells.
Based upon the lack of conclusiveness in the analysis, Larsson says there is no reason for women to stop drinking milk. Dairy products can help protect women from colorectal cancer, which is far more common than ovarian cancer.
Larsson did point out that “in the future when we know more about possible interactions between milk consumption and genetic susceptibility, it might be that some women should not drink milk because of a high risk of developing ovarian cancer."
This year, about 22,220 new cases of ovarian cancer will be diagnosed in the United States, according to the American Cancer Society, and about 16,000 women will die from the disease.