The Side Effects of Hormones in Dairy

Today, some research on the effects of hormones in milk. And we start with a story about what happens to men within an hour of drinking dairy milk.

We’ve known for decades that women who eat meat have higher levels of estrogen in their blood. Compared to nonvegetarians, vegetarian women were found to have 45% lower levels of the most potent human estrogen. This may help explain the lower incidence of breast cancer among those eating more plant-based. Even semi-vegetarians who eat less meat than omnivorous women may have significantly lower estrogen levels. Why? Perhaps because vegetarian women excrete two to three times more estrogens in their feces than do their meat-eating counterparts. And why is that? Because the average fecal output of vegetarians can be twice as high. The thought is that because vegetarians eat the amount of fiber closer to that which is natural for our species, those relying more on plants have an increased fecal output, which helps pull excess estrogen out of the system.

It may also have something to do with the hormones present in animal products. For example, the higher average blood concentrations of estrogen associated with high dairy consumption would be consistent with milk as a major source of estrogens in the human diet. The reason we’re concerned is that the increased consumption of animal-derived foods may have adverse effects on the development of hormone-dependent cancers. Among dietary risk factors, these investigators were most concerned about milk and dairy products, because the milk we drink today is produced by pregnant cows with markedly elevated levels of both estrogen and progesterone. The genetic manipulation of dairy cows enables them to lactate throughout almost their entire pregnancies, which is why commercial cow’s milk contains large amounts of estrogens and progesterone these days. That may be why milk-drinkers have five times the rates of having twins compared to vegans—that’s how much of an effect dairy may have on our hormones.

But we don’t really know how much the hormones in dairy affects our hormones until we put it to the test. Researchers looked to see what happens when men and prepubescent children, who both would normally have low estrogen levels, chug a quart (950 ml) of cow’s milk in under 10 minutes. This is what happened to the men. Within an hour of drinking the milk, their levels of the estrogen estrone went up, and progesterone and testosterone significantly dropped within 60 minutes.

It’s funny, there are men who don’t want to drink soy milk because of the phytoestrogens— even though soy phytoestrogen normally does not have feminizing effects on men—yet they’re perfectly willing to drink cow’s milk, which has actual estrogen in it!

In children, researchers saw the same thing—the levels of estrogens flowing through their body within an hour of drinking milk more than tripled: estrone, the potent estrogen estradiol, the pregnancy estrogen estriol, and a progesterone metabolite. And half the kids couldn’t even finish the whole quart (950 ml) of milk.

There’s also another sex steroid hormone present in cow’s milk called 5alpha-pregnenedione (5alpha-P) that is a direct precursor to a type of testosterone that may not only drive acne but also promote prostate cancer.

Now, we’d like to see controlled clinical studies, but the problem is there is no control. Dairy without the offending estrogen does not exist. Even organic milk from cows who aren’t injected with extra hormones has growth hormones in it, because biologically, that’s the whole point of milk—to put a couple of hundred pounds on a baby calf.

The problem with humans drinking cow hormones is there’s no natural feedback loop. For our own hormones, if we have too much estrogen or something, our brain dampens it down. But our own protective feedback system is bypassed when our system is invaded by these dihydrotestosterone precursors in dairy products. See, the human endocrine system, our hormonal system, didn’t evolve under the influence of ingested dairy and other external hormones and growth factors, and we’re just not equipped to cope with such a quote-unquote “sneak attack.”

In summary, evidence suggests that consumption of dairy-sourced hormones, which aren’t subject to any innate feedback inhibition, may be the source of the steroid sex hormones that drive acne and at least prostate cancer. This is perhaps the most promising unifying hypothesis—or theory—to explain the cause of diverse conditions that blemish, scar, shorten, or take the lives of millions.

In our next story, we look at the effects of the female sex hormones in milk on men, women, and children.

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 in 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. “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.”

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 a birth control pill. So, would it really have an effect on human hormone levels drinking it?

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 a 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.”

Finally today, what role cow’s milk plays in the aging of ovaries.

When it comes to the amount of steroid hormones we are exposed to in the food supply, milk products, dairy products, supply about 60 to 80 % of ingested female sex steroids. I’ve talked about the effects of these estrogens and progesterone in men and prepubescent children: how milk intake can spike estrogen levels within hours of consumption. But in terms of effects on women, I talked about the increased endometrial cancer risk in postmenopausal women, but what about reproductive-age women? Might dairy hormones affect reproduction?

We’ve known dairy food intake has sometimes been associated with infertility; however, little is known with regard to associations with reproductive hormones or anovulation, meaning how might dairy do it, by affecting how the uterus prepares, or affecting the ovary itself. The researchers found that women who ate yogurt or cream had about twice the risk of sporadic anovulation, meaning failure of ovulation, so some months there was no egg to fertilize at all. Now, we know most yogurt these days is packed with sugar. Even Greek yogurt can have more sugar than a double chocolate glazed cake Dunkin’ donut. But they controlled for that, and the results remained after adjusting for the sugar content, which suggests that the risk of anovulation was independent of the sugar content included in many yogurts. Now, we don’t know if this was just a fluke, or exactly what the mechanism might be, but if women skip ovulations here and there throughout their life, might they end up with a larger ovarian reserve of eggs?

Women are starting to have their first baby later and later; there’s been a rise in women having babies in their late 30s, and 40s. And we used to think that women’s ovarian reserve of eggs stayed relatively stable until a rapid decline at about age 37, but now we know it appears to be more of a gradual loss of eggs over time, where there’s a steady loss starting at peak fertility at one’s 20s. This is measuring “antral follicle count,” which is an ultrasound test where you can just count the number of like next-batter-up eggs in the ovaries. It’s probably the best reflection of true reproductive age. It’s a measure of ovarian reserve—how many eggs a woman has left.

Okay, so what does this have to do with diet? Researchers at Harvard looked at the association between various protein intakes with ovarian antral follicle counts among women having trouble getting pregnant. Even though diminished ovarian reserve is one of the major causes of female infertility, the process leading to reproductive deterioration with age is still poorly understood. In light of women delaying pregnancy until older age, the identification of reversible factors that may affect the individual decline might be of significant clinical value.

They did ultrasounds on all the women and studied their diets, and concluded that higher dairy protein intake was associated with lower antral follicle counts, in other words: accelerated ovarian aging.

Significantly lower ovarian reserve at the highest dairy intake, which would be like three ounces of cheese a day, compared to the lowest dairy intake. Okay, but what do these numbers mean in terms of biological age? Is 16.9 down to 12.7 really that much of a difference? If you look at women with really robust ovaries, a follicle count of 16.9 would be like what you might see in a 36- or 37-year-old. Whereas 12.7, what you can see in women eating the most dairy, is like what you might see in a really fertile 50-year-old. So, we’re talking years’ worth of ovarian aging, between the highest and lowest dairy consumers.

While it wasn’t possible for the researchers to identify the underlying mechanism linking higher dairy protein intake to lower antral follicle count, they had several educated guesses. One: it could be the steroid hormones and growth factors; two: the contamination of milk products by pesticides and endocrine-disrupting chemicals that may negatively affect the development of these ovarian follicles and egg competence.

Regarding the hormones, studies suggest that commercial milk (derived from both pregnant and non-pregnant animals) contains large amounts of estrogens, progesterone, and other placental hormones that are eventually released into the human food chain, with dairy intake accounting for 60-80% of the estrogens consumed, as I mentioned before. Dairy estrogens survive processing, appear both in raw and commercial milk products, are found in substantially higher concentrations with increasing amounts of milk fat, with no apparent difference between organic and conventional dairy products—that’s important to realize. It’s not just cows that have been injected with growth hormones. These hormones are just in their bodies naturally. and once inside the human body, these bovine hormones get converted to estrone and estradiol, the main active human estrogens. And following absorption, bovine steroids may then affect reproductive outcomes.

It is imperative that further studies are designed to clarify the biology underlying the observed associations. This might be crucial, given that consumption of another species’ milk by humans is an evolutionary novel dietary behavior that has the potential to alter reproductive parameters and may have long-term adverse health effects.