There is now consistent and substantial evidence that the higher the milk consumption of a country, the greater their breast and prostate cancer risk. The highest risk of cancer death is found in Switzerland, Norway, Iceland and Sweden, countries that are among the biggest consumers of milk. In stark contrast, in most Asian countries the risk is minimal.  In such countries, where the diet consists mainly of wholegrains, vegetables, fruits, tofu, soya milk and other soya products – and where milk is not a normal part of the diet – people are generally healthier, and breast and prostate cancers are much rarer than in the US and Europe.
The problem with milk
The connection between milk an increased risk of cancer has been known for some time. Back in 1937, a group of 4,999 children in the UK took part in a long-term study recording their dietary habits year on year. Some 65 years later, those with a high dairy intake during childhood were found to have tripled their odds of having colorectal cancer.  There was a weaker association with prostate cancer risk and no association, in this study, with increased breast cancer risk. According to the National Cancer Institute (NCI), 19 out of 23 studies have shown a positive association between dairy intake and prostate cancer: “This is one of the most consistent dietary predictors for prostate cancer in the published literature… In these studies, men with the highest dairy intakes had approximately double the risk of total prostate cancer, and up to a fourfold increase in risk of metastatic or fatal prostate cancer relative to low consumers.” 
Another large study involving 63,550 people in Britain, known as the EPIC study (European Prospective Investigation into Cancer and Nutrition), found no clear association between milk consumption and breast cancer, but it did find a trend towards a higher risk for premenopausal women partial to butter, and also in those with high intakes of processed meats.  To date it appears that countries that are virtually milk-free have the lowest risk, and that, among Western countries, low milk intake means a low risk of colorectal cancer and prostate cancer in particular.
What’s in milk? Why would milk increase risk? Milk contains 38 different hormones and growth promoters. After all, that’s its job: to make cells grow. But one in particular is attracting a lot of attention. It’s called insulin-like growth factor, or IGF-1. It’s a naturally occurring hormone, found both in cow’s milk, breast milk and your blood. The more milk you drink, the higher your level. What this hormone does is stimulate growth. Blood levels of IGF-1 peak during adolescence, stimulating development of breasts in girls or the prostate in boys, then levels rapidly drop off as you get older. Not so if you keep guzzling milk and cheese. Milk not only contains IGF-1, a small part of which is absorbed into your blood, but it also stimulates the body to produce more of its own. It simply does what it’s meant to do – stimulate growth. It also stops overgrowing cells from committing suicide, a process called apoptosis. While you are a rapidly growing baby this is good news. But when the only overgrowing cells are cancer cells, this is especially bad news, because IGF-1 has also been found to directly stimulate the growth of cancer cells, with high levels being linked to an increased risk of breast, prostate, colon and lung cancer. [5a][5b]
Having a high IGF-1 level as a pre-menopausal woman just about doubles your risk of cancer overall. 
Studies on high IGF-1 levels
A Harvard University study showed that men who had the highest levels of IGF-1 had more than four times the risk of prostate cancer compared with those who had the lowest levels.  Two other major Harvard studies have shown that milk-drinking men have 30 to 60% greater prostate cancer risk than men who generally avoid dairy products. [8a][8b] In one of these, involving more than 20,000...