ORLANDO (FRONTLINE MEDICAL NEWS) – A greasy hamburger and fries and a chocolate milkshake may all earn the finger of blame when teens fret over acne. But which of these foods is the real culprit?

A growing body of data suggests it may be the milk – especially if it’s fat-free milk, according to Andrea Zaenglein, MD , who spoke at the annual meeting of the American Academy of Dermatology. Skim milk has been at the center of a long-simmering acne controversy, said Dr. Zaenglein, professor of dermatology and pediatric dermatology at Pennsylvania State University, Hershey.

A 2005 Nurses Health Study II analysis, comprising 47,355 women, refocused attention on the issue. The women all had physician-diagnosed severe acne as teenagers in 1989. In 1998, they filled out food frequency questionnaires, recalling, among other things, how much milk they drank as teens and the type of milk they drank. After controlling for a number of variables, the study found that whole milk intake increased the risk of acne by 16% and skim milk by 44% ( J Am Acad Dermatol. 2005 Feb;52[2]:207-14 ).

The same association was seen in a subsequent study of 4,273 teen boys, published in 2008. There was a 10% increased risk for acne associated with intake of whole or 2% milk, a 17% increased risk for 1% milk, and a 19% increased risk for skim milk ( J Am Acad Dermatol. 2008 May;58[5]: 787-93 ).

A prospective study of about 6,000 girls found similar risks associated with all types of milk: a 19% increased risk for whole milk, 17% for low-fat milk, and 19% for skim milk ( Dermatol Online J. 2006 May 30;12[4]:1 ).

These and other data prompted Dr. Zaenglein and her colleagues at Penn State to conduct their own study, a case-control study of 225 teenagers aged 14-19 years, with moderate or no acne. “We took teens with acne and compared them to acne-free controls. The difference is, we tried to find a better dietary measurement,” than a food frequency recall, which is an unvalidated tool susceptible to recall errors, she said. Instead, they conducted phone interviews to gather 24-hour food intake recall data on three separate occasions ( J Am Acad Dermatol. 2016 Aug;75[2]:318-22 ).

They found positive associations with total dairy and with nonfat dairy, but not with whole-fat or low-fat dairy. “The association was driven by the nonfat dairy,” Dr. Zaenglein said. “When we took nonfat [dairy] out of the total dairy, the association there was no longer significant.” They also found no significant association with body mass index, glycemic index, or glycemic load, she added.

“You have to wonder, what could this association between dairy – and skim milk in particular – be? Could dairy actually be involved in the pathogenesis of acne?” There are a number of proposed mechanisms, none of which have ever been confirmed, she said. “Could it be related to steroids? Milk is a very bioactive substance with estrogens and other hormones, but these are fat soluble and would be removed in skim milk.”

Another theory suggests that insulinlike growth factor-1, either in milk or endogenously stimulated by its consumption, may make a contribution. “People who are passionate about this have published prolifically about the activation of this pathway,” Dr. Zaenglein said, “but it remains speculative.”

She added, there are a plethora of studies showing milk’s benefits in many other areas, including the benefits exerted by milk’s medium-chain fatty acids on cardiovascular health, glycemic control, insulin regulation, and even obesity.

Finally, dairy’s importance to bone health in the United States can’t be ignored. In fact, dairy products are the most commonly recommended foods for ensuring adequate calcium intake in children, teens, and young adults.

“It’s really hard to make a firm recommendation to eliminate dairy, because, in this country, it makes up a good portion of the calcium teens need during their bone-building years, and kids are already at high risk for not meeting these requirements.”

National nutritional guidelines recommend 1,300 mg of calcium every day, which can be accomplished in three to five servings of dairy. “An 8-ounce glass of milk has 300 mg. Yogurt, cheese, and calcium-fortified juice are all highly accepted by teens. But, to get that same amount from vegetables, for example, you’d have to eat 3 cups of cooked kale. That’s a lot of kale,” Dr. Zaenglein said.

She had no relevant financial disclosures.

On Twitter @alz_gal