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