All animal products contain hormones, like estrogen and progesterone, because the animals that they came from naturally produce them. Some dairy farms give their cows growth hormones to increase milk production, and much research has been done on the negative effects this has on the human body, to the point where it is even banned in some European countries. (1) Dairy farms who want their milk labelled as organic are not allowed to do this. For dairy products to be labeled as “USDA Organic” they must come from a cow that has not been given growth hormones or antibiotics, the cows feed must have not been treated with pesticides and the cow must have had access to pasture.
Unfortunately, dairy products that are labeled “USDA organic” are still high in one hormone; estrogen. This is because all dairy cows are female, and for the cow to produce milk it must currently be or recently have been pregnant. Pregnancy, in animals or humans, increases hormones like estrogen to help get the body ready for birth and feeding. So, the milk that we are consuming from these cows, even if it is organic, is high in estrogen. Recently more research has come out showing the negative effects that consuming this exogenous estrogen (estrogen produced outside the human body) has on disease risk and overall health.
A study published earlier this year in an international pediatric journal looked at the effect’s dairy has on adults; men in particular. They gave study participants a quart of cow’s milk and monitored their estrogen levels as they drank it. Within an hour of drinking the milk the male’s estrogen levels increased 60% and their testosterone levels significantly dropped. (2) But what does this mean for our health?
Natural hormone levels in the body are highly regulated by many metabolic processes. Any outside influence on these levels has consequences on the processes that they play a role in. For example, an athlete who supplements with high levels of testosterone to improve their strength can cause testicular degeneration and completely deplete their body of natural testosterone. Estrogen consumed in the diet is not at levels high enough to cause an extreme event like that, but it can lead to the disturbance of other hormone controlled bodily functions. Current research shows that this exogenous estrogen effects acne, reproductive health and can lead to certain cancers; including testicular and prostate cancer. (3) This hormone imbalance affects everyone but is most detrimental to children and adolescents as their natural hormones are constantly changing during this time. The Harvard Nurses’ Study “High school dietary dairy intake and teenage acne” studied the association between dairy intake and hormone levels. They found a positive association with an increase in teenage acne and milk intake, and concluded that drinking milk or consuming dairy products puts us at risk for exposure to high amounts of exogenous hormones that can throw off our own hormone levels during our teenage and adult years. (4) There is conflicting research on the extent that dairy leads to cancer; but it is known that estrogen from dairy can play a role in provoking the onset of tumors leading to cancer. (5) Research shows an association between high dairy consumption and increased risk of certain cancers; particularly prostate and testicular.6 But there isn’t enough research to clearly state a cause and effect relationship between the two.
So should we cut out all dairy from our diet? Even if it is organic? This is still unclear. More research needs to be done to prove that hormones, like estrogen, from dairy causes cancers and disease instead of just an association; but there is an increasing body of evidence. So for now be wary of where your dairy products come from and don’t overload on milk; organic or not.