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Hormones, milk and fat
I find it difficult to understand why the hormone content of skim milk is greater than that of 2% low-fat milk, which in turn is greater than whole milk (“Scientists find a soup of suspects while probing milk’s link to cancer,” SN: 3/28/09, p. 5). To the extent that 2% and skim milk are produced from whole milk, removing some or essentially all the fat, I would have expected the relation to be reversed. Is there an explanation for why the hormone content of milk increases as fat is removed?
Jerry Kerrisk,Santa Fe, N.M.

The researchers were just as perplexed as the reader about why the data turned out this way. — Janet Raloff

A few questions on the piece about hormone levels in milk: 1. There was no mention of organic versus “conventional.” Do you know if that was looked at? 2. Would goat’s milk have the same issues as cow’s milk? 3. Are there similar levels of hormones present in different types of dairy products, such as yogurt, kefir and cheeses? 4. What about the use of recombinant bovine growth hormone, or rBGH, in dairy cows and its presence in milk?
I would appreciate a more extensive follow-up. This article pretty much left the issues hanging, especially since a food like yogurt has been a human dietary staple for centuries.
Julia Pollock, Sebastopol, Calif.

The research discussed in the article focused only on conventional, store-bought cow’s milk, so it did not look at hormone levels in organic or goat’s milk products. It also didn’t address farmers’ use of rBGH.
Earlier work by others has found that little hormone makes it into dairy products like yogurt, cheese, ice cream and butter.
The cancer link to dairy goods, such as it is, appears focused on liquid milk. In fact, a few studies have suggested that consumption of fermented milk products — namely yogurts and cheeses — is associated with a decreased risk of some cancers.
Another possible confounder: Cows that produce a greater volume of milk likely do so because of natural hormonal (including estrogen) differences, researchers note, so breeding for higher-yielding cows may increase — or at least vary — the hormone concentrations present in lactating animals and their milk. However, studies have not yet been done to confirm this. — Janet Raloff


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Comments 2
  • The others have already commented, but my 'before reading' note was: Lawrence Joel Schiff                                                                                
                                                                                            321 E. 12th St., #4
                                                                                            NYC, NY 10003
        Salt, Fat, Carbs, Milk Estrogen?    [feel free to edit for size]            5/31/09

        People at Science News,
        In a recent review(SN 3/28/09 p5-6) of milk's potential link to cancer, the amount of estrogen(& other hormones) were inversely correlated to fat content -- the less milkfat, the more potentially active estrogen etc.
        I'm profoundly confused. I understood that fat cells were also hormone producing cells -- but why should the most hormone be progressively concentrated toward the 'leanest' milks -- skim, and buttermilk(where the butter is presumably residual)?
        What is concentrating the hormones as the fat is removed -- & why don't the hormones follow the fat, as they are also, presumably initially associated in fat cells? Is this concentration equivalently present & available -> active in 'dry(skim) milk'?
        Does the use of hormone stimulation in cow milk production increase this net 'estrogen load'? Does the lack of such stimulation significantly limit it in such milks?
        If 'temporarily inert' 'conjugated estrogens' are less bioavailable, & take longer to get from gut to blood, does a significant fraction exit the gut before entering the blood, or is this 'longer' still not significant re. their eventual absorption & transformation into more bioactive forms?
        Significant heat deactivates proteins. Are such hormones similarly denatured? Is some form of Pasteurization, or other treatment, sufficient to curdle activity, or otherwise prevent/filter out such titers on a commercial scale?
        What would indicate a milks estrogen etc. load, or how to find milk that doesn't have it?
        Inquiring minds & bodies want to know.
    Joel schiff Joel schiff
    May. 31, 2009 at 5:13pm
  • As far as the different contents are concerned, all that's required is that the hormones reside primarily outside of the milk's fat. Take whole milk and assume none of the hormone is found in the fat. Remove the fat until it's 2% fat, and you have still the same amount of hormone, but a smaller volume of milk making for a higher percentage or by-volume hormone content. Remove all the fat to make skim milk, and you have even less milk but with still the same hormone content. We know there is plenty of hormone outside the fat because skim milk has the "most hormone content." The same is true of lactose, calcium and other non-fat components of milk: there is a higher density in low fat and higher still in skim milk of anhthing not found "in the fat."
    Mark Bruni Mark Bruni
    Jun. 18, 2009 at 1:10pm
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