The Zit List

In years past diet was thought to be a significant factor in the onset of acne, particularly in teenagers. As research continued, however, dietary factors were largely discounted. That was based on the discovery that acne formation involved two primary mechanisms: an excess level of sebum, a fatty secretion that both moisturizes the skin and clogs skin follicles, and a type of bacteria called P. acnes that feeds on the excess sebum. Sebum formation is promoted by androgens, such as dihydrotestosterone (DHT) and DHEA. The bacteria produce irritating by-products that lead to inflammation and subsequent blocking of the skin follicles.

A recent study suggests that diet may be a factor in acne flare-ups after all.1 A longitudinal study of 47,355 nurses begun in 1989 looked at female health and diet habits. The women answered questions about their diets during their high school years, and the effects of various foods on the incidence of acne was examined in that population. The foods included typical teen favorites, such as french fries, pizza and chocolate.

Skim, or fat-free, milk showed the highest relationship to acne, as did instant-breakfast drinks, cream cheese and cottage cheese, as well as saturated fat and trans fat. Supplemental vitamin D showed a relationship to acne, yet the natural form of the vitamin found in food did not.

What is it about milk that may lead to breakout? The authors suggest that the culprit is the hormonal content of milk’estrogens, progesterone, androstenedione, 5-alpha-androstenedione and DHT. Milk also contains glucocorticoids, insulinlike growth factor 1 and other active peptide hormones. The big controversy is whether those substances survive the digestive process. Some studies show that native milk proteins, including casein, appear to promote hormone uptake by protecting them from the usual enzymatic digestive process.

Milk also contains testosterone in amounts that vary from 0.02 to 0.15 micrograms per liter. The average young girl produces about 32 micrograms a day of testosterone in her body. Testosterone, however, would not be a likely factor in acne because all oral testosterone undergoes rapid first-pass metabolism in the liver. Indeed, the behavior of oral-dose testosterone led to the development of oral anabolic steroids, which are forms of the hormone structurally altered to resist initial liver breakdown.

Milk’s content may be a more significant problem. Studies show that IGF-1 can be absorbed orally by newborns, but there is scant evidence to show that adults can absorb it orally. As a long string of amino acids in a specific sequence, IGF-1 should degrade like any other protein supplement. On the other hand, some studies show that native milk proteins shield IGF-1 from digestion, and what’s absorbed drives the effects of other hormones, such as glucocorticoids and androgens, that are linked to acne incidence.

High serum levels of IGF-1 and androgens show up in adults who have acne. In teens the primary hormonal culprit is DHEA, an adrenal androgen secreted by both sexes. Many formerly acne-free women who use DHEA food supplements report developing it.

The finding that skim milk shows a greater relationship to acne than whole milk leads the authors to suggest that its metabolism may somehow increase the bioavailability of factors in milk that promote acne. Whole milk may be a lesser factor because of its higher estrogen content, but it’s hard to understand how skim milk could have more active hormones, since so many are removed with the fat content of milk. If anything, the processing of skim milk would tend to inactivate hormones.

The study raises some interesting questions. The authors contend that milk products contain active hormonal factors that survive digestion, though that’s never been shown to occur in adults. If milk did contain active hormones, such as androgens and IGF-1, it would affect diseases related to them. For example, breast and prostate cancers are accelerated by IGF-1, which promotes rapid cell division, and cancer is a disease of uncontrolled cell division and mutation.

And another thing: If milk does contain active pro-hormones, shouldn’t it fall under the ban on pro-hormone food supplements that went into effect last January? A good argument against the ban is that those hormones exist naturally in milk and aren’t added. That, however, was the same rationale that enabled pro-hormone supplements to be sold in the first place: They, too, occurred in natural forms in many foods.

The dairy industry has thus far remained silent on the issue of milk and acne. Doubtless it’s reluctant to change the advertising slogan from ‘Milk is for every body’ to ‘Milk is for every pimple.’ IM

1 Adebamowo, C.A., et al. (2005). High school dietary diary intake and teenage acne. J Am Acad Dermatol. 52:207-14.