En español | A recent study out of California's Loma Linda University showed a strong correlation between cow's milk and higher breast cancer rates, a link previously considered unfounded by most experts.
The study used food questionnaires to follow nearly 53,000 North American women (mean age of 57) for almost eight years. What they found when they combed through results: Higher intakes of dairy milk were associated with a greater risk of breast cancer — up to 70 to 80 percent higher for those who drank two to three cups a day, with a lesser but still observable increase in risk for those who drank just one-quarter to one-third a cup daily.
"We were able to look at people on the low end of milk consumption right up through people who were drinking pints of milk a day,” says principal researcher Gary Fraser, M.D., a professor of medicine and epidemiology at Loma Linda University Health.
The study did not see a difference in risk between participants who drank whole milk and those who drank reduced-fat milk (the researchers were unable to test whether the milk was organic). And though the group studied had fairly high soy consumption, the researchers found “no convincing evidence” that soy products were associated with a higher risk of breast cancer. In fact, there was a marked reduction in risk when substituting soy milk for an approximately equivalent quantity of dairy milk, researchers found. They also discovered that other types of dairy, like cheese and yogurt, had neither an “adverse nor protective” effect on breast cancer risk.
Although only a double-blind experiment could definitely prove a link to breast cancer, Fraser notes that his team carefully controlled for other factors that might create the false impression of a connection in this type of research. “We adjusted for alcohol consumption, for different dietary products and for a whole battery of reproductive factors, like whether the women had taken oral contraceptives, breastfed their kids or had taken hormone replacement therapy after menopause.” As he tells it, none of those factors seemed to explain the results, leading him to the conclusion that “there may be some other mysterious factor, but it does look like dairy milk is at least interesting in terms of a possible breast cancer cause."
Fraser points out that studies about dairy's effect on breast cancer risk have shown varied, or even contradictory, results over time. “Milk has been an area of controversy for a long time,” echoes Marisa Weiss, M.D., founder and chief medical officer of Breastcancer.org. “Patients get frustrated when one day the advice is ‘Drink milk’ and the next day it's ‘Don't drink milk.’ “
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For her part, Weiss recommends exercising caution. “There's a precautionary principle in public health that it's better to be safe than sorry. Humans are at the top of the food chain, so we are vulnerable to anything we eat. There are reasons to believe that some foods are healthier than others, and some have risks. Milk is a product that comes from animals, and the health of the milk depends on the health of the cow, including whether it has extra hormones in it."
Weiss describes her general approach as sticking to organic fat-free dairy milk and then to “mix it up by also drinking other kinds of plant-based milks — soy milk, almond milk, hemp milk, oat milk or rice milk.” But there are a couple of caveats, she cautions: “Make sure the milks are unsweetened, and stick with organic soy milk, because over 80 percent of soy products are grown using chemicals. Also, make sure that if you drink less dairy milk, you find another source for calcium and vitamin D, which helps build strong bones and bodies."
Dawn Mussallem, D.O., a diagnostic breast specialist at the Mayo Clinic in Jacksonville, Florida, notes that the American Institute for Cancer Research (AICR) has no recommendation on milk and breast cancer and that though this study suggests an association between milk consumption and breast cancer risk, it does not say that milk directly causes the disease.
"When counseling a woman who is not at an increased risk for breast cancer,” Mussallem says, “I would let her know that research to date on milk consumption and breast cancer has been inconsistent, and I would highlight the benefits of milk for adults, including that it provides beneficial nutrients like calcium and is an affordable source of protein, and that there has been convincing evidence linking milk with a decrease in colorectal cancer risk.” For a postmenopausal woman who is at an increased risk of breast cancer, however, she says she would “discuss with her the AICR guidelines and the available studies on milk and breast cancer so she can make her own decision."
Overall, Mussallem says, “Cancer is a very complex process. Drinking milk isn't going to cause cancer.” When it comes to reducing your risk for cancer, she says, the following guidelines are well accepted: Maintain a healthy weight; be physically active; eat a diet rich in vegetables, fruit, whole grains and beans; limit fast foods and sugary drinks; limit red meat and stay away from processed meat; and avoid alcohol. “It's about your overall lifestyle,” she adds. “And when it comes to milk consumption, the advice needs to be individualized, like everything in medicine."