by Neal D. Barnard, M.D.Could milk cause prostate cancer? The question has come up repeatedly in recent months, as billboards portraying New York City Mayor Rudolph Giuliani with a milk mustache carried the words, "Got Prostate Cancer?" The outraged mayor countered that milk had nothing to do with his newly diagnosed disease, which also killed his father. For the public, this was completely new territory. Does drinking milk actually contribute to cancer?
Here are the facts: Major studies suggesting a link between milk and prostate cancer have appeared in medical journals since the 1970s. Two of six cohort studies (research studies following groups of people over time) found increased risk with higher milk intakes. Five studies comparing cancer patients to healthy individuals found a similar association. One of these, conducted in northern Italy, found that frequent dairy consumption could increase risk by two and one-half times.1
In 1997, the World Cancer Research Fund and the American Institute for Cancer Research concluded that dairy products should be considered a possible contributor to prostate cancer. And yet another research study came out in April 2000 pointing to a link between dairy and prostate cancer: Harvard's Physicians' Health Study followed 20,885 men for 11 years, finding that having two and one-half dairy servings each day boosted prostate cancer risk by 34 percent, compared to having less than one-half serving daily.2
A Smoking Gun?
Researchers are looking, not only at whether milk increases cancer risk, but how. The answer, apparently, is in the way milk affects a man's hormones. Dairy products boost the amount of insulin-like growth factor (IGF-I) in the blood. In turn, IGF-I promotes cancer cell growth.3-5 A small amount is normally in the bloodstream, but several recent studies have linked increased IGF-I levels to prostate cancer and possibly to breast cancer as well.
Milk does other mischief. Its load of calcium depletes the body's vitamin D, which, in turn, may add to cancer risk. Most dairy products are also high in fat, which affects the activity of sex hormones that play a major role in cancer.
And it would come as no surprise that milk might affect the growth of cancer cells. After all, its biological purpose is to support rapid growth in all parts of a calf's body. After the age of weaning, calves (like all mammals) have no need for milk at all, and there is never a need to drink the milk of another species.
Researchers are investigating whether dairy products might be culprits in other forms of the disease. Ovarian cancer, in particular, may be linked to galactose, a sugar produced from the milk sugar lactose. Yogurt, cheese, "lactose-free" milk, and other dairy products contain substantial amounts of galactose.
Other parts of the diet affect cancer risk, too. Meat and fatty foods in general are implicated in increased risk, while tomatoes, watermelons, and other bright red fruits contain lycopene, which reduces cancer risk.
The bottom line: While researchers will study the causes of cancer for years to come, health-conscious families may well want to trade dairy—and all animal products—for a healthy, vegan diet rich in vegetables, fruits, whole grains, and legumes. When to make the switch? Evidence suggests that the earlier in life healthy diet habits begin, the better your protection.
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What?! Does Everything Cause Cancer?
As a matter of fact, no. Whole grains, beans and other legumes, vegetables, and fruits are cancer fighters. Plant foods are low in fat, high in fiber, and loaded with protective cancer-fighting nutrients. But animal products—meat, dairy, eggs—are linked to several forms of the disease. They contain plenty of fat to harbor cancer-causing chemicals and to drive up the levels of cancer-promoting hormones in your body. They have no fiber that would normally sweep carcinogens from your digestive tract and are low in cancer-fighting antioxidants. And under cooking temperatures, the creatine, amino acids, and natural sugars in meat can actually turn into cancer-causing chemicals.
A cancer-prevention diet includes plenty of:
Vegetables: sweet potatoes, carrots, broccoli, spinach, asparagus
Fruits: strawberries, kiwi, melon, bananas, apples
Whole grains: breads, cereal, oatmeal, pasta, rice
Legumes: beans, peas, lentils
The most healthful diets eliminate meat, dairy products, eggs, and fried foods. To make the transition easy, you may wish to use rice milk, soymilk, meat substitutes, or egg substitutes.
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References
1. World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition, and the Prevention of Cancer: A Global Perspective. American Institute for Cancer Research, Washington, D.C., 1997, p. 322.
2. Chan JM, Stampfer MJ, Ma J, Ajani U, Gaziano JM, Giovannucci E. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. Presentation, American Association for Cancer Research, San Francisco, April 2000.
3. Cohen P. Serum insulin-like growth factor-I levels and prostate cancer risk—interpreting the evidence. J Natl Cancer Inst 1998;90:876-9.
4. Cadogan J, Eastell R, Jones N, Barker ME. Milk intake and bone mineral acquisition in adolescent girls: randomised, controlled intervention trial. BMJ 1997;315:1255-60.
5. Heaney RP, McCarron DA, Dawson-Hughes B, et al. Dietary changes favorably affect bone remodeling in older adults. J Am Dietetic Asso 1999;99:1228-33.
