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Milk Can Cause Cancer
Category: Cancer CureEstrogens can fuel the growth of many tumors, even in the prostate–and estrogen can do this at amazingly tiny concentrations. Identifying how estrogens’ prevalence varies by milk type, and in what chemical form the hormones occur, required a new assay, which the NCI scientists describe in an upcoming issue of the Journal of Chromatography B.
Using that technique, they showed that the mélange of estrogens varies widely between milks. Whole milk contained the smallest quantity of estrogens, and amounts ascended from 2% to skim and buttermilk. In all of these milks, the majority of estrogens had undergone a minor chemical modification, rendering them less directly bioavailable and less hormonally active.
However, these modified, or conjugated, estrogens are not inert, and they can be converted back to their more potent parent compounds.
What’s more, the NCI scientists note, studies by others have shown that relative to free, bioavailable estrogens, conjugated ones take longer to get from the gut into the blood.
Veenstra’s team concludes that compared with free estrogens, milk’s conjugated ones “are likely to have longer half-lives.”
Overall, skim milk had the smallest quantity of free estrogens. However, the conjugated type that dominated skim milk’s profile, 2-hydroxyestrone, is known to be one of the most reactive and potentially risky of the metabolites, notes Xia Xu, a toxicologist on the NCI team. That metabolite’s concentration in fat-free milk was second only to buttermilk’s.
Dermatologist F. William Danby, who teaches at Dartmouth Medical School, also worries about other sex hormones in milk—the “male” androgens.
While estrogens may fuel tumor growth in reproductive tissues, certain androgens—ones that Danby refers to as 5alpha-reduced androgens—“have the capacity for increasing the number of estrogen receptors.” In the January/February Dermato-Endocrinology, Danby notes that milk contains at least one receptor-proliferating androgen: 5alpha-pregnanedione.
Extra receptors, he explains, permit more estrogen—including any from milk—to unlock the cellular machinery that can turn tumor growth on. In other hormone systems, when excess hormone shows up, the body often cuts back on its production. Because the body has had relatively little evolutionary time to adapt to dietary sources of the 5alpha-reduced androgens, Danby says, no such feedback system has evolved.
“And this is probably the most important thing,” he says. Milk-derived hormones “are being poured into a system that didn’t anticipate them”—at least in adulthood.
One of the most provocative aspects of the milk story is its impact on insulinlike growth factor 1. Many studies have linked elevated concentrations of IGF-1 with cancer risk. Not only is milk a rich source of the substance, but people who drink milk also end up with more IGF-1 in their blood.