The Dark Side of Milk

  • 5 Jul 2009
  • Reading time 5 mins
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Should milk be a staple food? Does it increase cancer risk? Here I interview top scientist Professor Jeff Holly.

Q: What is IGF?

PJH: IGF stands for ‘Insulin-like Growth Factor’. As with the hormone insulin, it is a small protein. It is one of the most highly concentrated of the protein hormones in blood. Blood contains around a thousand times higher amounts of IGF than most other protein hormones and it has profound effects on stimulating growth and metabolism. It is present in all of us and is clearly a key hormone, influencing many aspects of our health. IGFs, for example, mediate the effects of growth hormone on childhood growth. There are two types, IGF-1 and IGF-II, but these are always present with one of six other proteins, IGFBP-1 to -6, and they activate a number of tissue receptors including IGF-1R, IGF-IIR and the insulin receptor. Unravelling their complex roles is one of the frontiers of endocrinology.

Q: How does drinking milk influence our IGF levels?

PJH: Milk contains lots of hormones and growth factors including IGF, although when we drink it most of these are digested. Only a very small amount, protected in the gut by the milk protein casein, makes it into our bloodstream. This isn’t, however, the only way in which milk creates an increase in blood levels of IGF. The cocktail of hormones, small proteins and amino acids in milk stimulates our own production of IGF, the net result being that IGF-1 levels in the blood increase as a result of drinking milk. To put this in context, if you were aged 20 to 30, you might normally have something like 170 ng/mL of IGF-1 in the blood. If your diet is high in dairy products you might have a level of 200 to 210 ng/mL. If you don’t drink milk your level might be 130-140ng/mL. IGF-1 levels are highest in teenage years, at the height of teenage sexual development, then decline rapidly in adulthood. In this graph, for example, you see the IGF-1 levels in men, aged 50-70, according to milk consumption. Those who have a pint or more of milk per day, compared to those with less than half a pint a day, have increased their IGF by about 25 ng/ml. This is a highly significant increase.

Q: Does this increase in IGF from milk drinking increase cancer risk? The full content of this report is only viewable by 100% Health Club members.

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