Vegan Society Briefing

Milk and Breast Cancer (1 of 7)

Stephen Walsh, November 2001.

Summary

In August and September 2001 there were claims in the press that drinking milk could reduce the risk of breast cancer. Dairy Council nutrition manager Anita Wells said, "To discover that life-long milk drinkers have a reduced risk of breast cancer is an exciting step forward." "Good health starts with dairy," said Greg Miller, executive vice president of nutrition and scientific affairs for the National Dairy Council.

These claims were triggered by a prospective study of premenopausal women in Norway, published on 15 September 2001 in the International Journal of Cancer. This study found a significantly reduced risk of breast cancer in women who reported high milk consumption both as adults and as children compared with women who reported low milk consumption both as adults and as children. The risk of breast cancer among the high milk group appeared to be about half the risk in the low milk group.

If this had been one of many studies finding similar results, the claim of a protective effect would have some credibility. However, considering other prospective studies on breast cancer and dairy products shows that this is not so. One study found a significant increase in risk with milk consumption and another found a significant increase in risk with cheese consumption. A Finnish study agreed with the recent Norwegian study that there was a protective association with milk products. Two other studies found no significant association, with one finding a tendency to a beneficial effect and the other finding a tendency to an adverse effect. The authors of the most recent study state, "The contradicting results may indicate that any association between milk and breast cancer is not a strong one." This seems a fair conclusion. Indeed, if a true effect exists there is no reason to assume it will prove to be beneficial. The suggestion that consuming milk reduces breast cancer risk is therefore unjustified.

Some reports latch on to a constituent of dairy fat - conjugated linoleic acid (CLA) - as a likely explanation for the suggested beneficial effect, suggesting that milk fat might benefit health. Neither of the two prospective studies which found a beneficial association of milk with breast cancer showed a link with milk fat. The more likely explanation for any beneficial effect, if one exists, is the calcium and vitamin D content of the milk. Even if CLA showed some benefits, it must be recognised that it is only a small part of dairy fat and that breast cancer is only one aspect of health. Milk fat is highly saturated and promotes elevated cholesterol, which is strongly linked with heart disease. Milk fat is therefore a very unlikely choice as a health food. Calcium and vitamin D can of course be obtained from many sources other than dairy products.

Consuming milk increases levels of a growth hormone, IGF-1, in the body. Increased IGF-1 levels are strongly implicated in prostate cancer, colorectal cancer, premenopausal breast cancer and lung cancer. The effect of milk on IGF-1 may be due to absorption of IGF-1 from the milk or may simply be due to the high protein and zinc content of the milk.

For those concerned with their risk of breast cancer and with their overall health there are useful recommendations to consider. Weight gain in adult life increases breast cancer risk. Physical activity helps in maintaining a steady weight and also has additional benefits in reducing risk. Olive oil provides a healthful alternative to saturated fats. Alcohol consumption increases risk of breast cancer, even at moderate levels, but this increase in risk can be effectively countered by high folate intakes. As moderate alcohol intake is associated with reduced risk of heart disease, increasing folate intake may be a better option than cutting out alcohol altogether. Folate is found in green leafy vegetables and many other plant foods and can also be obtained from folic acid supplements. Adequate B12 may be needed to get the full benefit of folate. Adequate calcium and vitamin D may also be beneficial.

There is a lot we can do to take control of our health for the better, including reducing risk of breast cancer. Green leafy vegetables, olive oil and physical activity can all be expected to be beneficial. Drinking cow's milk doesn't appear on the list.

Good information supports health. Pass it around.

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