My post last Friday concerned my ‘love-hate’ relationship with dairy products – I generally like the way they taste, but am also acutely aware that they can quite-often trigger health issues in myself and others. I first leaned this when the elimination of cow’s milk products 20-odd years ago eliminated my eczema too. Other symptoms and conditions that are often linked to dairy-sensitivity include asthma, gut symptoms and ENT issues including sinus/nasal congestion and catarrh.
One other condition that has been linked with dairy consumption is acne. I remember a few years ago a campaigning group in the U.S. would hand out information urging teenagers to eschew milk (and perhaps other dairy products) on the basis that they could cause acne. If I remember rightly, the literature was adorned by cartoon-type images of children with acne-afflicted skin drinking milk.
I was reminded on the supposed link between milk and acne by a comment that came after my post last Friday. The commenter asked me to comment. I thought I’d at least have a look to see if there was any literature at all on this. It turns out that indeed there is.
The evidence in this area comes from what are known as ‘epidemiological’ studies which look at associations between things, but cannot generally be used to prove that one thing is causing another. However, to prove a causal link would require studies in which individuals are fed dairy products or ‘placebo’ dairy products (foodstuffs that look and taste like dairy products but are not actually made from animal milk) to see what effect, if any, these have on individuals’ propensity to acne. The chances of such studies being done are, well, virtually zero. So, it makes sense to at least look at what the epidemiological evidence shows.
I can find three studies in the area, and all of them show some association between milk consumption and heightened risk of acne [1-3]. The first of these studies [1] found that those drinking the most milk were more likely to have acne, and that this association was highest for skimmed milk. This first study was a so-called ‘case control’ study, which essentially takes a snapshot of a factor (e.g. milk consumption) and a disease (e.g. acne) in time.
While these studies are of some value, they are generally considered inferior to so-called ‘cohort’ studies (sometimes referred to as ‘prospective’ studies) which assess, say, dietary habits and disease risk over time. The two remaining studies in the area are cohort studies. One [2] looked at girls, and the other [3], boys. In girls, consuming two or more servings of milk each day compared to less than one serving a week was associated with about a 20 per cent increased risk of acne. For boys, the apparent risk increase was of a similar magnitude (about 16 per cent).
If milk does cause acne, how does it do it? Milk, it turns out, has the ability to induce the secretion of the hormone insulin [4]. Insulin secretion can drive the secretion of a related substance known as insulin-like growth factor 1 (IGF-1). One effect of this is to raise testosterone levels (heightened levels of male hormones – androgens – can cause acne). It is, of course, possible that other characteristics of dairy products (e.g. hormones) might also affect acne risk.
Other foods that, in theory, might enhance acne risk through their effects on insulin/IGF-1 are those that release sugar relatively quickly into the bloodstream (high glycaemic index and high glycaemic load foods). Some evidence supports this association. For more on this, see here.
References:
1. Adebamowo CA, et al. High school dietary intake and teenage acne. J Am Acad Dermatol. 2005;52(2):207-14.
2. Adebamowo CA, et al. Milk consumption and acne in adolescent girls. Dermatol Online J. 2006 May 30;12(4):1
3. Adebamowo CA, et al. Milk consumption and acne in teenaged boys. J Am Acad Dermatol. 2008;58(5):787-93.
4. Hoyt G, et al. Dissociation of the glycaemic and insulinaemic responses to whole and skimmed milk. Br J Nutr 2005;93(2):175-177
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