Acnegenic effect of milk not a myth

National report - Results from an analysis of data from the Nurses Health Study II (NHS II) cohort provide conclusive evidence of a positive association between the development of severe acne and intake of milk, says F. William Danby, M.D.

The mechanism underlying that association is postulated to involve effects on the pilosebaceous follicle of hormones and other bioactive molecules found in milk, and its clinical implication is that a "no milk" diet may be considered as a therapeutic intervention for acne.

"While results from studies conducted during the 1930s and 1940s pointed to an association between milk intake and acne, they were too small to demonstrate a statistically significant effect. The NHS II data provides enough power to prove the relationship, and there is biological plausibility for it because milk is a complex substance containing many hormones that make things grow. However, dietary restriction trials are the only way to test the hypothesis," says Dr. Danby, who is a lecturer, department of medicine, section of dermatology, Dartmouth Medical School, Hanover, N.H.

Dr. Danby was a coauthor of the study (J Am Acad Dermatol. 2005;52:207-214) investigating the association between milk and acne and encouraged its undertaking by Walter Willett, M.D., Dr.PH, and his colleagues at the Harvard School of Public Health. NHS II has data on approximately 116,000 women, of whom about 40 percent (47,355) completed a validated, semi-quantitative food-frequency questionnaire about diet during their high school years. The information from that survey was used to divide the participants into seven groups based on frequency of milk intake. Using the lowest intake group (<1 glass/week) as the reference group, multivariate analyses were performed to determine prevalence ratios of physician-diagnosed severe acne with increasing milk intake.

Women in the highest total milk intake group (>3 glasses/day) were found to have a statistically significant, 22 percent increased prevalence of severe acne compared with the reference group. An even stronger association was found between severe acne prevalence and skim milk intake - in that analysis, there was a 44 percent increased rate among women in the highest versus lowest intake groups.

Supporting data

Papers are now being prepared for publication from two other studies that provide corroborating evidence of an association between milk intake and the development of severe acne. Those studies analyzed data from the male and female participants of the Growing Up Today Study, who represent the sons and daughters of the NHS II subjects. The children included in those studies were in the 9- to 15-year-old age range, and so, not surprisingly, an effect of milk on acne risk is best demonstrated in the female cohort.

"Age of acne onset is typically later among boys, and so we hope to continue to follow them and analyze the data again when they are older," Dr. Danby says.

Multimodal mechanisms

Dr. Danby and his colleagues postulate that milk influences acne development through direct and indirect effects of its components on the pilosebaceous follicle. Milk contains a large number of steroid hormones and other bioactive compounds that may promote formation of comedones and inflammatory acne lesions by stimulating sebum production and hyperkeratinization of the pilosebaceous follicle. In addition, they may have acnegenic effects secondary to their ability to increase plasma IGF-1 levels.

However, Dr. Danby also believes that genetic susceptibility plays a role in acne development caused by dietary milk intake. He proposes that all individuals have their own genetically determined "acne threshold" hormone level, which, if exceeded, leads to the development of acne. The threshold level may be passed when endogenous hormone levels rise, such as due to stress or menstrual cycle variations, or as a result of exogenous exposure from milk.

Milk avoidance

Removing milk from the diet is one strategy to avoid passing the hormone acne threshold, and Dr. Danby suggests a six-month dairy-free trial to evaluate the benefits of milk restriction. In his patients, dairy-free means absolutely no milk, cheese, butter or ice cream.

"The trial must be of sufficient duration to remove the stimulus and allow resolution of sebaceous gland activity along with the secondary inflammation and infection," he explains.