Spot the culprit: How milk can trigger acne
For decades scientists have searched for the causes of acne. Now a study has identified one of the key triggers: milk. Sanjida O'Connell finds out how a pinta causes pimples
Tuesday, 8 May 2007
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Julianne never suffered from spots as a teenager, but by the time she was 28 she had terrible cystic acne along her jawline and across her neck. An American, she had travelled to Europe to learn to become a cook and a sommelier.
She decided to open a deli as well as a restaurant back in the States, so before she returned home she toured Europe, sampling every cheese she could find. As she recounted her story to the dermatologist Bill Danby, something clicked: "Oh my God, it's the cheese," she said. For six months, she cut out all dairy products. During that time she became 85 per cent free of acne, and her skin has continued to improve.
Milk has been anecdotally linked to acne for almost a century but, so far, few scientists have agreed on the real cause of acne and even fewer believe that diet plays a major role. Danby, who runs a private practice in Manchester, New Hampshire, and also works at Dartmouth Medical School, believes that milk does indeed cause acne - and that he knows what the mechanism could be.
Acne can affect anyone at any age, but it usually peaks at between 16 and 18, when up to 98 per cent of the population of Western countries is affected. A link between diet and acne has been suggested because acne is less common in other countries but increases when a Western diet is adopted. As well as being socially excruciating, acne is costly - £2bn is spent each year treating it.
Danby, who has long held that there is a link between diet and acne, persuaded Dr Walter Willett and his colleagues at the Harvard School of Public Health in Boston to look into the matter. The team studied more than 47,000 women who are part of a research project called the Nurses Health Study II.
The women were asked to complete questionnaires relating to their diet as teenagers and to say whether they had ever been diagnosed with severe acne. The study found no link between food such as chocolate and chips and acne, but found one between women who had acne and those who had drunk a lot of milk.
But why should milk, such an essential bone-building nutrient, be bad for our skin? Willett believes it's because of the hormones in the milk, and Danby has taken this argument a step further. What most dermatologists usually agree on is that the male hormone testosterone (also found in women), changes to dihydrotestosterone (DHT) in the sebaceous glands, the oil-producing glands in the skin. Acne is produced when the hormone causes too many of the cells that line the duct of the gland to be produced too quickly. Unable to separate from each other, they stick together and form a plug in the pore - the first visible sign of acne.
Of course, everyone will respond differently to hormones. As Danby says: "The ability to develop acne is partly genetic and partly the result of hormone exposure. I tell my female patients that genetics are the key to the fact that Paris Hilton has lots of money and no zits and my patients have lots of zits and no money. It is all genetics."
The milk most of us drink is produced by cows for their calves. To ensure maximum milk yields cows are inseminated days after giving birth to their calves, which are taken away. A dairy cow will spend most of its life being milked and being pregnant at the same time.
So milk is full of hormones: not only ones intended to help the calf grow, but also those produced by the placenta to aid the cow's pregnancy. They include DHT, and other hormones that are the pre-cursors to DHT. In other words, the hormones teenagers naturally produce are plentiful in milk. It of course contains other growth-enhancing hormones too - as Danby says: "Milk is, after all, specifically designed to make things grow."
Another worrying hormone, as far as acne is concerned, is IGF-1. This "growth factor" peaks at age 15 in girls and 18 in boys, coinciding with peak acne levels. IGF-1 is thought to works with testosterone and DHT to cause acne. IGF-1 is present in cows' milk anyway, but levels rise by 10 per cent when cows are given injections of recombinant bovine growth hormone (rBGH) to increase milk yield. Drinking organic milk is not a solution because the cows are still pregnant while lactating, so they have the same hormones in their milk as non-organic cows.
Danby's solution is to eliminate dairy from the diet - after all, he says, the Perricone diet is practically dairy-free. Nicholas Perricone, an American dermatologist who has launched a range of skin products, has also developed a skin-food diet based on eating large amounts of wild salmon.
However, Perricone's London-based nutritionist, Christopher Lee, disagrees with Danby: "A diet high in sugars and saturated fats is rich in free-radical-causing agents, which will exacerbate acne. But acne is triggered by hormones and is not caused by diet."
Saturated fats may play a role, but the Harvard Nurses study found that acne was most closely linked to skimmed milk. The researchers hypothesise that it is not the fat that is the problem, but the hormones, which may be altered. For instance, to give skimmed milk a creamier texture, whey is often added, and the protein in whey can make other hormones more reactive.
The Dairy Council isn't convinced, saying the study is flawed because, first, it asked participants to remember what they ate a decade ago and, second, it shows a link between milk and acne, which is not the same as proving that milk causes acne.
Dr Judith Bryans, the director of the Dairy Council, says: "Science does not support links between acne and dairy foods," and argues that, "unnecessary exclusion of dairy from the diet can compromise nutrient intakes. This is especially important for teenagers who are most likely to suffer with acne, and for whom the bone-building nutrients found naturally in dairy foods are so important."
To address this, another long-term study is about to be published, looking at the Harvard Nurses' teenage children, who should have no problem remembering what they're eating and how many spots they have.
Danby agrees with the Dairy Council that the link between acne and milk is unproven: "My dermatological colleagues insist, with justification, on a full double-blind randomised controlled trial. But so far it has been impossible to arrange such a trial. Double-blinding dairy intake is essentially impossible because we have no hormone-free dairy we could feed people as a 'placebo'."
However, in defence of his dairy-free stance, he adds: "Objectively, human consumption of large volumes of another species' milk, especially when that milk comes mainly from pregnant cows during the human's normally post-weaned years, is essentially unnatural."
