The Dangers of Hormones in Dairy Products

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“The milk we drink today is quite unlike the milk our ancestors were drinking.” -Dr. Ganmaa

During a presentation back in December, Ganmaa Davaasambuu, a physician, Ph.D. in environmental health, and working scientist at the Harvard School of Public Health, discussed some of her concerns related to cow dairy and the risk of developing hormone-dependent cancers. While the relationship between these cancers (commonly of the breast, testes, and prostate) and dietary hormones has not been widely studied, it is a shared concern among many scientists.

According to Ganmaa, “Among the routes of human exposure to estrogens, we are mostly concerned about cow’s milk…Dairy accounts for 60 percent to 80 percent of estrogens consumed.” Modern dairy farms typically milk their cows 300 days per year, and throughout much of that time the cows are pregnant. Hormones in milk increase as a cow progresses further into pregnancy. For example, during the late stage of pregnancy, a cow’s milk will have as much as 33 times the level of estrone sulfate (an estrogen compound) compared with milk produced from a cow that is not pregnant.

After comparing modern milk in Japan to raw milk from Mongolia, Ganmaa found that the Japan milk had 10 times the levels of another hormone, progesterone, than the Mongolian raw milk. Ganmaa pointed out that in Mongolia and other traditional herding societies, cows are milked for only five months out of the year for human consumption. When a cow is pregnant, she is only milked in the early stages of her pregnancy. These practices correspond to much lower levels of hormones being present in the milk.
“The milk we drink today is quite unlike the milk our ancestors were drinking,” noted Ganmaa. According to her, “The milk we drink today may not be nature’s perfect food.”

There is some evidence that dairy consumption is linked with a higher risk of certain cancers. In one study, diet and rates of cancer were compared in 42 countries. Interestingly, consumption of milk and cheese products corresponded strongly with incidence of testicular cancer in men. Incidence of this particular cancer was lowest in countries like Algeria, where consumption of dairy products are much lower. An increased death rate from prostate cancer has been found to be correlated with increased consumption of dairy products over the past several decades in Japan. Milk and cheese consumption has also been linked with elevated risk of breast cancers.

Ganmaa mentioned the results of another study, where rats given milk developed more tumors and showed an increased incidence of cancer compared with rats who drank water.

More research is needed to more deeply understand the effects of consuming dairy products. Ganmaa’s work clearly shows us that we should pay more attention to and further examine the differences between commercially-produced and traditionally-produced dairy.
As a way of reducing human exposure to hormones, Ganmaa suggests that we either avoid milking pregnant cows altogether or avoid milking them as they approach later stages of pregnancy. These seem like reasonable suggestions coming from the perspective that the milk a mother produces as she gets ready to give birth is probably specifically designed for the newborn-to-come, as opposed to consumption by humans.
Dr. Shana McQueen