SKINIPEDIA - Skin Encyclopedia: Milk Consumption and Acne
Milk consumption and acne in adolescent girls - CONCLUSIONS
Study by Clement A Adebamowo, Donna Spiegelman, Catherine S Berkey, F William Danby, Helaine H Rockett, Graham A Colditz, Walter C Willett, Michelle D Holmes, Dermatology Online Journal
Conclusions
In this prospective study of US girls whose ages ranged from 9 to 15 years in 1996, we found that greater consumption of milk was associated with higher prevalence of acne. We did not find an association with dairy fat. This suggests that the fat content of milk is not important in comedogenicity. This finding is consistent with the result of our previous study of US female nurses who reported on their high school diet and prevalence of physician-diagnosed severe teenage acne. In that study, we found a positive association with intake of total and skim milk.
Milk intake may affect acne severity through the Insulin-like Growth Factor-1 (IGF-1) pathway. In two large cross-sectional studies, milk consumption was positively associated with higher plasma IGF-1 levels and in both studies, this was predominantly an association with skim milk. In a randomized clinical trial of the effect of milk intake on bone remodeling, intakes of skim and low fat milk were associated with increased serum IGF-1 levels in both sexes. It is not clear whether the increased IGF-1 is endogenous—released in response to milk intake—or exogenous IGF-1 from milk. Human and bovine IGF-1 share the same amino acid sequences and several milk proteins, including IGF-binding proteins (IGFBPs) protect IGF-1 from digestion in the gut. Animal studies have shown that milk borne IGF-1 can be absorbed after oral intake [24]. IGF-1 directly stimulates basal keratinocytes' proliferation. Although both serum androgens and IGF-1 levels rise at puberty, the period of maximum prevalence of acne and the course of the condition follow the levels of IGF-1 more closely than levels of androgens. There is also a stronger correlation in women between acne lesions and IGF-1 compared to androgens.
Milk intake may influence comedogenesis because it contains several bioactive molecules that can act on the pilosebaceous unit including androgens, 5α-reduced steroids and other steroid hormones. Many of these bioactive molecules survive processing and in the case of cheese, fermentation results in the production of more testosterone from precursors in milk. The level of androgens in milk has generally been considered low and first-pass metabolism in the liver may further reduce its bioavailability compared to the daily endogenous production in young children and adolescents. However, recent studies have questioned the methodology and assays on which estimates of daily production rates of endogenous steroid hormones in pre-pubertal children are based. Dietary intake may be a more significant source of androgens than previously thought. Milk also contains estrogens, some of which are produced in the lactating bovine mammary gland and are direct suppressors of sebaceous gland function.
Some hormones in milk are carried by whey proteins, including α-lactalbumin, which also have intrinsic biological functions. Animals fed α-lactalbumin-enriched whey protein show increased will and capacity to engage in physical activities, gains in lean body mass, improved efficiency of exercise training, and decreased percentage body fat mass; all of which are similar to the effect of androgens. In addition, α-lactalbumin undergoes pressure-induced conformational alteration, possibly because of centrifugation stresses during processing; this leads to changes in biological function. Whey proteins are also added to low fat and skim milk to simulate the consistency of whole milk. These proteins might therefore play a role in acne. We note an inverse association with cream cheese, which may be due to reverse causation because girls with acne may avoid cream cheese in the belief that it is associated with acne. The group of girls who regularly eat cream cheese may also be too small to draw conclusions. Alternatively, the fermentation phase of cheese production is associated with changes in the relative concentration of bioactive molecules in cheese that may explain this finding.
Vitamin D, present in milk because of fortification, plays an important role in epidermal differentiation by inhibiting the proliferation of keratinocytes and this could possibly affect acne risk [39]. However, supplemented vitamin D was not associated with acne prevalence in this study (PR = 1.02, 95% CI = 0.96, 1.08 for highest compared to lowest quartile of intake, p-value for test for trend = 0.81). This suggests that vitamin D was not responsible for the observed association with milk consumption.
Although some of the girls in this study did not respond to the questionnaire that included the question on acne, we do not think that this is likely to bias our result because this is a prospective study and response rate was not appreciably related to milk consumption or to teenage acne. We did not have an opportunity to validate the self-report of teenage acne but other studies have shown that young people's perception of acne severity is closely related to objective clinical assessment. Our sensitivity analysis also shows that our results are robust to different ways of classifying acne in our study population. We did not exclude girls whose acne may be part of the symptom complex of an underlying clinical disorder because we did not have data on this; had we, the association with milk consumption may have been stronger. Our questionnaire did not specify a body location for the acne. However, truncal acne, with absence of a facial component occurs in less than 5 percent of sufferers.
The dietary assessment that we used has been well validated and the use of energy-adjustment corrects for over- or under-reporting of overall dietary intake. We computed Mantel-Haenszel prevalence ratios, a method that intrinsically controls for main effects and higher order interactions of all confounders, whether these confounders are relevant or not. It leads to loss of statistical power and gives a conservative estimate of effect. For example, the odds ratio (95% CI; p-value for test of trend) from the multivariate logistic regression analysis adjusted for age at baseline, height and energy intake comparing the highest (2 or more servings per day) to lowest (<1 serving per week) categories of skim milk intakes in 1996, were 2.27 (1.47, 3.52; <0.001).
In conclusion, our study suggests that milk may have biological effects in the consumer. Because milk contains androgenic hormones and other bioactive molecules, moderation of milk intake may be useful as part of the management of teenage acne. Furthermore, this finding raises the possibility that other hormone-sensitive glands may be affected by the hormonal constituents of milk. Because of the potential detrimental effect of milk products on acne, breast cancer [42], and prostate cancer, these relationships should be evaluated further.