LOMA LINDA, Calif. — Growing up, so many of us were constantly reminded to drink milk. Milk is indisputably a great source of protein and calcium, but a new study has come to a troubling conclusion regarding dairy milk: regularly drinking milk can seriously increase a woman’s chances of developing breast cancer.
Researchers at Loma Linda University say that even relatively small amounts of milk intake can raise a woman’s risk of suffering from breast cancer.
Gary E. Fraser, the study’s first author, says that the findings supply “fairly strong evidence that either dairy milk or some other factor closely related to drinking dairy milk is a cause of breast cancer in women.”
“Consuming as little as 1/4 to 1/3 cup of dairy milk per day was associated with an increased risk of breast cancer of 30%,” he explains in a release. “By drinking up to one cup per day, the associated risk went up to 50%, and for those drinking two to three cups per day, the risk increased further to 70% to 80%.”
These results are even more shocking when one stops to consider the fact that U.S. dietary guidelines actually recommend that everyone drinks three cups of dairy milk daily. In light of the study, Dr. Frasier suggests that Americans “view that recommendation with caution.”
The research team studied the diets of almost 53,000 North American women for nearly eight years. At the beginning of the research period none of the participating women showed any signs of cancer at all. The women filled out diet questionnaires, were periodically asked to write down what they ate and drink over 24-hour periods, and also completed an initial baseline survey that asked about demographic information (family cancer history, exercise and alcohol habits, past breast cancer screening, etc).
After the conclusion of the observation period, 1,057 breast cancer diagnoses had occurred. While eating soy products didn’t increase the women’s odds of developing breast cancer, dairy calories and dairy milk did show a connection. The more dairy calories and the more milk a woman reported drinking, the more likely she was to develop breast cancer. Rather surprisingly, there were only minimal variations in the results across full fat milk, low fat milk, and no fat milk. The study’s authors also found no “important associations” regarding cheese and yogurt consumption.
“However,” Fraser says, “dairy foods, especially milk, were associated with increased risk, and the data predicted a marked reduction in risk associated with substituting soymilk for dairy milk. This raises the possibility that dairy-alternate milks may be an optimal choice.”
As far as how or why milk appears to be contributing to breast cancer, researchers believe it may have something to do with sex hormones present in dairy milk. It’s common for roughly 75% of any given dairy herd to be pregnant, and breast cancer in women is a hormone-responsive cancer. Also, eating lots of dairy and animal protein has been linked to higher blood levels of a certain hormone (IGF-1) believed to promote cancers.
“Dairy milk does have some positive nutritional qualities,” Fraser concludes, “but these need to be balanced against other possible, less helpful effects. This work suggests the urgent need for further research.”
The study is published in the International Journal of Epidemiology.