“Does milk give you boobs?” and other udderly important questions about dairy. Part 1!

Sixteen. I did not get my period until I was 16.  I could legally drive a car before I was even beginning to become something that wouldn’t resemble a boy with braids or a sheet of cardboard stuck atop two beanpoles. My doctor thought it was because I was too active and skinny, so my mom started making me huge bi-daily milkshakes. A little less than a month later, I finally got it.

“Oh, it’s the hormones” all my mom’s friends knowingly nodded. (Why they were all sitting around discussing my menses is not the topic of this blog, albeit a legitimate question.) Were they right? Is there estrogen in milk, and can it cause little girls to grow up / guys to get C-cups / people to get cancer / and hey, while we’re at it, serve as a cheap form of birth control? 

OMG, cow’s milk has estrogen?

Yes, milk has estrogen because it comes from the cow’s “breast”… But wait guys (and gals!) before you dropkick your latte into the street, let’s put it in perspective. Three 8-oz glasses of milk has been shown to average about 68 ug  (MICROgrams) of estrogen compounds.  But, your body, (yes, YOUR body) makes a lot more! Prepubescent girls make 54,000 ugs/day, pre-pubescent boys: 100,000 ugs / day; full-grown men: 140,000 ugs/day, and pre-menopausal women: 630,000 ugs / day.  So, the amount of estrogen anyone makes in their body can be 800 – 9000 times greater than the amount in 3 glasses of milk.

Guys make estrogen?

Wait, guys make estrogen?

Yup. Except the reason you cried during Toy Story 3 is because you’re human.

Hooray! Free birth-control!!

Interesting idea, but no. I actually overheard this conversation in a Starbucks. Some guy was cracking himself up trying to (impress? entertain? break up with?) his girlfriend by saying “you know those lattes have hormones in them. You have so many that maybe you don’t need to take the pill anymore. It’s like…the morning-after latte!”

Good one, buddy. But let’s find out why he may have only read the first sentence of any article on the subject…

Being sweet, the girl answered with a giggly wide-eyed “yeah! Nice idea!” Inside, you could tell she was thinking: “Brilliant idea, babe. But did you know that the FDA has an extensively researched guideline assuring us there are no physiological effects of estrogen when we consume less than 1% of how much estrogen we already make?  So, hmmm, in my venti latte that’s like, what, 57 ugs, which is like less than 0.01-0.1% of the values either you, myself, or even your two little monster siblings produce.

Also, my little stud muffin, this guideline is assuming that the estrogen in milk actually gets into my body as estrogen…it largely doesn’t!  First, since I’m not injecting my latte into my veins, the amount of estrogen that actually gets in is only 2-5%; that’s like, 1.4 – 3.4 micrograms.  Secondly, I’m sure since you’re so smart you know that scientists found 90% of the estrogen in cow’s milk to be in an inactive form; so 90% of that 57 ugs is inactive to begin with. So the amount of active estrogen that’s even making it into my body is really, really tiny.

But yeah, great idea, honey. What would you like to name our baby?”

OK. So no free birth control. But will milk give me cancer?*

Given the low amounts and poor absorption of estrogen-like compounds, and the unlikelihood of them being active in the first place, this would be a biochemical stretch. On the real life side, one of the only in-human studies you can do to determine if something causes cancer is what’s called an epidemiological or correlational study.** A recent review of the correlational evidence we have found that the the recommended level of 3 servings per day is safe; consuming dairy products does not consistently increase the risk of prostate cancer, and may be protective against bladder, breast, and colon cancers.***

So aside from milk apparently not being that bad, there are a lot of things about dairy products that are good!**** But I’m trying to break these blogs up to make them shorter, so stay tuned for research-based answers to questions about dairy products and health promotion, what’s up with the claims about weight loss, and other burning calcium queries that are keeping you awake at night. (If you have any, send them along!)

Marily O.

MS, RD, PhD

PS- The answer to the question of whether or not milk made me a woman is probably no. There is some weak evidence that greater milk intake is associated with an earlier age of puberty onset, but it’s correlational (see below) and it is probably not due to the estrogen. The best guess (and since “confirmed” by guesses of several of my doctors) is that given my active lifestyle, the calories in the milkshakes finally provided me with enough surplus energy for my body to develop the possibility of healthfully housing another. It may or may not have to do with IGF, (see below) but no literature yet supports that. Current studies are looking into the bioactive components of milk, however, so stay tuned.

* Milk also contains Insulin-like Growth Factor-1 and 2. We already have this in our body, and it is similar to that in milk. The IGFs are typically inactivated during processing for cheese, yogurt, and other products, but not during pasteurization (which is the common processing done to milk that we drink). The following review cites many studies that considered the potential IGF pathway towards cell proliferation in cancer development, and concluded that from what we know so far, the IGF does not increase the risk of cancers.

Chagas, C.E.A., Rogero, M.M., & Martini, L.A. (2012). Evaluating the links between intake of milk/dairy products and cancer. Nutrition Reviews, 70(5), 294-300.

** Often the design that is used is what’s called a prospective design, where the researchers ask people what they ate, how they exercise, take their BMI and other biological markers of health, and then periodically assess them over the years. They watch and “wait” in a sense to see who gets what diseases, then they look for patterns or associations between certain diseases and certain diet or health parameters. This is not a causal link, however!

*** It’s important to note that these correlational studies cannot show causation. Even though they show link between milk consumption and a decreased risk of some cancers, and try to control for other things such as exercise, BMI, fruit and vegetable intake, etc, it is still only an association. Scientists can only speculate the direction and possible biomechanical explanation for why one might be found with the other. Therefore, correlational studies are often stepping stones for more focused controlled research. People who drink milk may be doing something else that the questionnaire did not ask, and so it only seems like milk is doing the cancer risk decreasing.

**** Unless, of course, you are lactose intolerant, in which case you know that milk is no walk in the health park for you.

More Sources:

Macrina, A.L., Ott, T.L., Roberts, R.F., & Kensinger, R.S. (2012). Estrone and estrone sulfate concentrations in milk and milk fractions. Journal of the Academy of Nutrition and Dietetics, 112(7), 1088-1093.

Parodi, P.W. (2012). Impact of cows’ milk estrogen on cancer risk. International Dairy Journal, 22, 3-14.

Wiley, A.A. (2011). Milk intake and total dairy consumption: Associations with early menarche in NHANES 1999-2004. PLoS ONE 6(2), e14685.

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3 responses

  1. Fantasic article.

    I have been looking for an article like this that debunks all those crazy thoughts on milk. You hit most of my thoughts based on the reseaech on the mark!

    I follow a Peatarian diet so dairy is a staple but people think im crazy for because all thehormones and cancer etc etc blah blah.

    P.s. not sure if you know who ray peat is but in that case I recommend looking some of his material up.

    Again good article!

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