Vegan Society Briefing

Milk and Breast Cancer (6 of 7)

Stephen Walsh, November 2001.

Reducing breast cancer risk and promoting health

In contrast to the statements from dairy industry representatives, milk does not seem to be the answer to breast cancer. Calcium and vitamin D may have a beneficial role. However, even these do not rank in the established dietary recommendations for reducing breast cancer incidence.

Walter Willett, a nutritional epidemiologist with the Harvard School of Public Health and the American Institute for Cancer Research makes the following recommendations for avoiding breast cancer [15].

• Avoid weight gain in adult life.
  
• Limit alcohol intake to moderate amounts.
  
• Ensure sufficient folate (or supplementary folic acid) intake to avoid the excess risk associated with even moderate amounts of alcohol.
  
• Replace saturated fat with olive oil.

Willett does not mention milk, though high-fat dairy products are implicitly rejected in favour of olive oil as they are a major source of saturated fat. Willett does not suggest a direct adverse role for saturated fat in breast cancer, but rather a benefit to health from replacing it with olive oil, a particularly healthful source of monounsaturated fat. The recommendation of olive oil as opposed to rapeseed/canola oil or other oils high in monounsaturated fats is deliberate: there is specific evidence for a benefit from olive oil over and above its major constituent fats. The recommendation to substitute olive oil for saturated fat appears to be based on evidence for positive benefits of olive oil in relation to breast cancer and the fact that substituting olive oil for saturated fat will improve blood cholesterol levels and thus reduce risk of heart disease.

Willett does not recommend completely eliminating alcohol, as moderate intakes of alcohol appear to have beneficial effects on heart disease. He notes that the adverse effects of alcohol in promoting breast cancer appear to be completely eliminated by high folate intake, allowing the benefit to be obtained without the damage. Folate is particularly well supplied by green leafy vegetables but is present in many other plant foods as well. In supplements it usually takes the form of folic acid. Some of the effects of folate are dependent on the presence of adequate vitamin B12, so vegans should ensure an adequate B12 intake (about 3 micrograms per day) to ensure that they get the full benefit of folate.

Willett takes a sceptical stance towards soy products due to recent evidence that they can stimulate proliferation of breast tissue, potentially increasing the risk of breast cancer. The overall effect of increased soy intake is more likely to be adverse in postmenopausal women than in premenopausal women due to interactions with oestrogen. He therefore suggests that "soy products should be used in moderation if started during midlife, perhaps no more than a few times a week, until further data are available". Typical Japanese and Chinese consumption is about 10g of soy protein (about 300ml (half a pint) of soya milk or 100g (4oz) of tofu) per day, consumed with apparent lack of adverse effects. Indeed, both these populations show low levels of breast cancer. However, their consumption of soy is from an early age and this is likely to be relevant. Overall it seems prudent not to exceed Japanese levels of consumption significantly, particularly if soy consumption is started late in life.

One of the more surprising observations is the comment that in the largest prospective study on dietary fat and breast cancer to date (pooling results from multiple studies) women consuming less than 15% fat showed double the risk of breast cancer [16]. No details of the particular diet characteristics of this group are given, but this observation adds to reasons for caution about very low fat diets.

A review paper by Timothy Key and Naomi Allen [17] provides an alternative summary of risk factors for breast cancer, concluding that obesity in postmenopausal women and alcohol consumption are the only well established diet-related risk factors for breast cancer. They conclude, "Current dietary advice should be to avoid obesity, limit alcohol intake and to maintain a varied diet."

Willett makes some more general observations on diet and cancer in [18]. He emphasises the need to make choices that are beneficial for both cancer and heart disease - we can only eat one diet.

Willett does not regard the evidence against meat as clear enough to make a strong recommendation regarding breast cancer. However, he notes that the evidence against red meat in relation to colorectal cancer is much stronger.

While the evidence for fibre and whole grains in relation to cancer is weak, Willett comments that there is stronger evidence in relation to heart disease, diabetes and diverticular disease and this justifies a recommendation that increased cereal fibre consumption is likely to be beneficial for health.

Willett also emphasises that physical activity reduces risk of colorectal and breast cancer directly, as well as by reducing weight.

Finally, Willett estimates that remaining lean (BMI < 25), taking at least 30 minutes a day of moderate physical exercise, avoiding excessive alcohol consumption, getting plenty of folate, not smoking, and consuming red meat less than three times a week could reduce colorectal cancer by 70%.

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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