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Milk and Prostate Cancer: The Evidence Mounts
By Neal D. Barnard, M.D.
Could milk cause prostate 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.
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.
References
1. World Cancer Research Fund/American Institute for Cancer
Re-search. 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.
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