Study Finds That Consumption of Natural Estrogens in Cow's Milk Does Not Effect Reproductive Health

Estrogens found in food have been thought to play a negative role in human reproductive health, but until now, researchers have not been sure of the exact connection between the two.

A particular area of concern was bovine milk, which is known to contain naturally occurring estrogens.

The study examined how different concentrations of estrogens in milk affected the following parameters in mice: plasma levels of natural estrone (E1) and 17β-estradiol (E2); uterine weight in females; and testosterone levels, testes weight, and seminal vesicle weight in males.

The three levels of E1 and E2 tested were concentrations similar to native milk from a pregnant cow (0.093 ng/mL for E1 and 0.065 ng/mL for E2), milk with an added 10 ng/mL of E1 and E2, and finally milk with an additional 100 ng/mL of E1 and E2.

The results of the study demonstrated that consumption of milk from a pregnant cow did not raise plasma levels of E1 and E2 in mice. It also did not affect the weight of the sex organs examined in either male or female mice.

The same results were found for the milk containing an additional 10 ng/mL of E1 and E2; however, investigators did find that when the concentration was raised to 100 ng/mL, effects were seen in the mice.

"We did observe elevated plasma estrogens in both sexes, increased uterus weight in females, and decreased plasma testosterone levels in males from the group that received milk with an added 100 ng/mL of E1 and E2," said senior co-author Gregor Majdic, DVM, PhD, Vice Dean, Center for Animal Genomics, Veterinary Faculty, University of Ljubljana. "However, concentrations in the third group exceeded the physiological concentration of milk estrogens by 1,000 times, so it would be extremely unlikely to find such concentrations in native cow milk."

Previous studies have shown that the gastrointestinal and hepatic systems are capable of inactivating large amounts of estrogens before they reach other parts of the body, and this fact may explain why naturally occurring estrogens in milk appeared to have little impact on the mice.

"In our study," stated Dr. Snoj, "it is likely that plasma E1 and E2 did not increase in mice drinking pregnant cow's milk because the estrogens in the milk were at low enough levels to be metabolized during first liver passage and did not reach systemic circulation."

However, more research is needed to examine the effect estrogen from milk has on the development of the reproductive system before and during puberty.

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