New research from Sweden suggests that drinking more than one glass of milk a day may double the risk of ovarian cancer. But experts say dairy's benefits are clear and results don't mean women should stop drinking milk.
The study's investigators say more research is needed to confirm the association, but the findings are not the first to link dairy foods to ovarian cancer. Several large investigations conducted in the U.S. also suggested an association, but other studies have shown no link.
"Basically the picture is far from clear, and women would really be doing a great disservice to their diet if they took dairy out of it because of this," American Dairy Council spokeswoman Deanna Rose, RD, tells WebMD.
"The benefits of dairy are clear for bone health, and recent studies have also suggested that dairy foods can help lower blood pressure and are also beneficial for people trying to lose weight."
Milk Showed Strongest Association
Researchers from Sweden's Karolinska Institute followed more than 60,000 women for an average of 13.5 years. The women completed detailed questionnaires on the foods they ate and other lifestyle factors. Over the course of the study 266 were diagnosed with ovarian cancer.
After taking other known ovarian cancer risk factors into account, researchers found that women who ate four or more servings of dairy foods a day — including milk, yogurt, ice cream, and butter — had twice the risk of developing serous ovarian cancer, one of the most common forms of ovarian cancer. No association was seen between dairy and other forms of ovarian cancer.
Milk was identified as the dairy product with the strongest positive association with ovarian cancer. Study participants who drank more than one glass of milk a day had twice the cancer risk as those who drank one glass or less a day. Serving sizes were defined as the average size the women consumed. The research is published in the November issue of the American Journal of Clinical Nutrition.
Several studies have suggested that eating low-fat or nonfat dairy products helps protect against ovarian cancer, but the fat content of the dairy foods did not appear to influence risk in the Swedish study.
Rather than fat, the study's researchers suggest that the sugar lactose found in dairy products may explain their findings. They point out that at least one study has shown that a lactose component known as galactose can promote ovarian cancer.
The study did not show any significant increase in ovarian cancer with other dairy products alone, such as yogurt, cheese, ice cream, or butter.
Weighing the Evidence
The studies assessing the role of dairy products in ovarian cancer have been contradictory. But American Cancer Society (ACS) spokeswoman Debbie Saslow, PhD, says the best of them do suggest a link. A report from an ongoing study involving 80,000 nurses in the U.S. published in 2000 found a 44 percent increase in ovarian cancer risk among frequent vs. infrequent milk drinkers.
Saslow says though the investigations suggest an association, none has proved that eating dairy causes ovarian cancer. She is director of breast and gynecological cancers for the ACS.
"I wouldn't want women to take from this study or the evidence as a whole that they should not drink milk or drink less milk," she tells WebMD. "Everything is a trade-off, and you have to weigh the risks and benefits. The benefits of dairy are apparent."
Known Ovarian Cancer Risk Factors
The cause of ovarian cancer is not yet known, but certain factors increase the chance of getting ovarian cancer:
—Family history of ovarian cancer
—Having never been pregnant
—Being over the age of 50, since the likelihood of developing ovarian cancer increases with age
Studies show that women who have had children, who breastfeed, or who use birth control pills are less likely to develop ovarian cancer. These factors decrease the number of times a woman ovulates, and studies suggest that reducing the number of ovulations during a woman's lifetime may lower the risk of ovarian cancer.
By Salynn Boyles, reviewed by Michael W. Smith, MD
SOURCES: Larsson, S. American Journal of Clinical Nutrition, November 2004; vol 80: pp 1353-1357. Susanna Larsson, Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden. Deanna Rose, RD, spokeswoman, National Dairy Council. Debbie Saslow, PhD, director of breast and gynecological cancers, American Cancer Society. WebMD Medical Reference provided in collaboration with The Cleveland Clinic.
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