Does drinking cow’s milk raise estrogen levels in humans?
You might think this question would have been thoroughly vetted by the Food and Drug Administration. But, to our knowledge, only one small study has examined it.
Marayuma, et al. (2010, Japan) had three groups of people drink milk and then tested some of the impacts. The groups were young men (n=7), prepubescent children (n=6), and menstruating women (n=5).
Note that estrogen has three different forms: estrone (E1), estradiol (E2), and estriol (E3). E1 can be converted into E2, the most potent form. E3 can be made from E1 and E2, but cannot be converted into E2.
The young men drank 4 to 5 cups of 3.5% fat milk in 10 minutes. Their serum levels of hormones were then measured over the next 2 hours. Serum E1 was slightly elevated, but there was no significant increase in E2. Progesterone also increased, while testosterone decreased. The men also had significantly elevated levels of E1, E2, and E3 in their urine.
The children drank 2.0 to 2.5 cups of milk. Only their urine estrogen levels were measured, which significantly increased.
The five women drank two cups of milk before bedtime. The researchers only measured the impact on their menstrual cycles. Four of the five women weren’t impacted, whereas the fifth woman, with a history of long cycles, didn’t ovulate until she stopped drinking the milk.
The authors write:
The activation of a negative feedback mechanism due to exogenous estrogens in cow’s milk indicates that men are affected by intake of commercial cow’s milk.
Exposure to exogenous estrogens through intake of commercial milk produced from pregnant cows has spread around the world since the 1970s. We think that the intake of pregnant cow’s milk is one of the major causes of early sexual maturation in prepubertal children….Since 1985, daily intake of cow’s milk has been extensively recommended, especially to prepubertal children in Japan. The average age of menarche in girls living in metropolitan Tokyo occurred at 12 years 5 months in 1987, and 12 years 3 months in 1993. These findings and the present data indicate that the intake of cow’s milk may cause earlier sexual maturation.
These results suggest that ovulation in women with subclinical hypogonadism might be affected by an abundant intake of milk, although normal menstrual cycles are not influenced.
This study has some limitations:
- The participants drank very large amounts of milk in a short time. This might have caused more significant increases or decreases in hormones than would be expected under more usual milk intakes.
- The study was very small.
- There was no control group to compare what happens when people drink, for example, another beverage with a similar fat or protein content.
