“The Effects of Hormones
in Dairy Milk on Cancer” All food of animal origin contains
hormones, but most of our dietary exposure to hormones
comes from dairy products. By quantity it’s mostly prolactin,
corticosteroids, and progesterone, but there are also a bunch of estrogens,
which then concentrate further when you make other dairy products, like five times more concentrated
in cream and cheese, ten times more hormone
concentration in butter. So when it comes to exposure to
steroid hormones in the food supply, about three-quarters of our exposure
to ingested female sex steroids comes from dairy, with
the rest evenly split between eggs, and meat and fish. Eggs contribute about as
much as all meat put together, which makes a certain
amount of sense since it comes straight
from a hen’s ovary. Among the various types of meat,
you get as much from white meat— fish and poultry—as you
do from pork and beef. And this is just from
natural hormones, not added hormone injections
like bovine growth hormone, so for these it doesn’t
matter if the meat’s organic. Animals produce hormones
because they’re animals, which understandably
ends up in animal products. But only about half of people
surveyed seemed to know that, lacking basic knowledge, like
not realizing what milk is for— cows only give milk
after having a calf. So these researchers suggested
we ought to inform the public about dairy production practices, to which one Journal of Dairy
Science respondent wrote: ya know, telling the public all our new
technologies, like transgenic animals, meaning genetically
engineered farm animals, or taking away that calf right away
so we can have more of the milk, or not letting cows see grass, may not actually result in
high rates of public approval. So, ixnay on the educationay. One thing with potential
public health implications that the public may not know about
is their exposure to estrogen through intake of commercial milk
produced from pregnant cows. See, modern genetically
“improved” dairy cows, such as the Holstein—your
standard black and white cow— can get reimpregnated
after giving birth and lactate throughout almost
her entire next pregnancy, which means that commercial
cow’s milk these days contains large amounts
of pregnancy hormones like estrogens and progesterone. Here’s the estrogen levels in
milk during the first eight months of a pregnant cow’s
nine-month gestation: hormone levels shoot
up more than 20-fold. But even so, we’re still only talking
about a millionth of a gram per quart, easily 10 to 20 times
less estrogen hormones than what you’d find in
like a birth control pill, so would it really have an effect on
human hormone levels drinking it? Here are the average levels
of three different estrogens and a progesterone metabolite
flowing through the bodies of seven men who then proceeded
to drink about a liter of milk. Within hours, their
hormone levels shot up. Here are the average levels
of these female sex steroids flowing through the bodies of six
schoolchildren, average age eight, before drinking about two
cups of milk, and then after. Within hours their levels shot up, tripling or quadrupling their
baseline hormone levels. So one can imagine the effects
milk might have on men or prepubescent children,
but what about women? Presumably they’d have such
high levels of estrogens in their body in the first place. Well, not all women. What about postmenopausal women
and endometrial cancer, for example? Estrogens have a central role in the
development of endometrial cancer, which is a cancer of the
lining of the uterus. Milk and dairy products are a source of
steroid hormones and growth factors that might have
these kinds of effects. So Harvard researchers followed
tens of thousands of women— and their dairy consumption—
for decades and found significantly higher risk
of endometrial cancer among postmenopausal women
who consumed more dairy. What about dietary exposure
to hormones and breast cancer? Unfortunately, “understanding the
role of dietary hormone exposure in the population burden of breast
cancer is not possible at this time.”