Consumer Health = Journal

Consumer Health Journal=20

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Hormones in Milk Are Linked to=20 Cancer

March=20 2004

by Alison=20 Stewart

Studies link dairy = consumption to=20 ovarian and breast cancer in women and prostate cancer in men. = Milk, both=20 human and cow, has naturally-occurring growth hormones that can = become=20 cancerous in adults, whose bodies are supposed to have finished = their=20 growth spurts.

Biology

    One=20 reason milk consumption may lead to cancer risk is insulin-like = growth=20 factor, IGF-1 (not to be confused with bovine growth hormone, = rBGH). Milk=20 contains IGF-1 for good reason: milk is designed for babies, and = IGF-1=20 helps us grow. IGF-1 affects growth, as well as other functions, = and is=20 normally found in our blood. Higher levels of IGF-1, however, = appear to=20 stimulate cancer cells.

     = "IGF-1 in milk is a=20 growth factor," said Dr. Amy Joy Lanou, nutrition director = for the=20 Physicians Committee for Responsible Medicine. "Adult bodies are = no longer=20 growing. Lots of excess growth factors floating around are likely = to find=20 cancerous cells to act upon," Lanou=20 said.

     Cow's milk has IGF-1, = and=20 IGF-1 levels increase in cows treated with bovine growth hormone, = rBGH.=20 (Estimates range from twice as high to ten times higher.) Also,=20 pasteurization does not destroy IGF-1, but increases its = concentration=20 instead.

There is IGF-1 in cow's milk = that is=20 identical to the IGF-1 found in humans already, which could lead = to the=20 ease with which we absorb it from milk. IGF-1 is found in higher=20 concentrations in the bodies of people who consume dairy=20 products.

Study=20 Analysis

"IGF-1=20 appears to be a very good indicator of cancer risk," said Dr. = Colin=20 Campbell, nutritional biochemistry professor at Cornell=20 University.

Though=20 diets high in calories or in animal proteins also boost IGF-1 = levels, milk=20 seems to be worse than other foods. A 1999 study showed that = adding three=20 eight-ounce servings of milk per day to the diet for 12 weeks = caused a 10=20 percent increase in IGF-1 levels. ("Dietary changes favorably = affect bone=20 remodeling in older adults" Journal of American Dietetic=20 Association, 1999). In 1997, a similar study had similar = results in=20 teenage girls. ("Milk intake and bone mineral acquisition in = adolescent=20 girls," British Medical Journal, 1997).

And in=20 terms of cancer causation, in pre-menopausal women, a 1998 study = found=20 that women with highest concentrations of IGF-1 had more than = twice the=20 risk of breast cancer as those women with lowest levels. = Interestingly,=20 there was no relationship between IGF-1 concentrations and breast = cancer=20 risk in post-menopausal women. ("Circulating concentrations of=20 insulin-like growth factor-1 and risk of breast cancer," = Lancet,=20 1998).

There are=20 conflicting results in other studies, however. A 2002 study = ("Intake of=20 Dairy Products, Calcium, and Vitamin D and Risk of Breast Cancer,=20 Journal of the National Cancer Institute, September 2002) = found an=20 association between intake of low-fat dairy products and a reduced = risk of=20 breast cancer. This could be because women who use low-fat dairy = products=20 are more likely to be health-conscious overall, or it could be = that some=20 forms of dairy help reduce cancer risk.

= Ovarian cancer=20 may also be linked to dairy consumption, but for a different or = additional=20 reason.

Our bodies break down = milk sugar,=20 lactose, into galactose. Enzymes then break the galactose into = more usable=20 sugars. When a woman's dairy consumption overloads the enzyme's = ability to=20 break down the galactose, it may build up in the blood or affect a = woman's=20 ovaries, according to the PCRM ("Women and Cancer," = source,=20 PCRM).

The PCRM=20 explains how a 1989 study of hundreds of women with ovarian cancer = found=20 that the difference between them and a similar age and demographic = group=20 of women who did not develop ovarian cancer was their dairy = intake,=20 particularly their intake of yogurt and cottage cheese. = ("Galactose=20 Consumption and Metabolism in Relation to the Risk of Ovarian = Cancer,"=20 Lancet, 1989.)

The=20 problem wasn't the fat in milk -- it was the sugar in milk, so the = bacteria in the yogurt and cottage cheese actually increased the=20 conversion of lactose to galactose.

In=20 addition to breast and ovarian cancer, prostate cancer may also be = linked=20 to dairy consumption. Neal Barnard, president of the PCRM, = analyzed 23=20 studies relating to prostate cancer and milk consumption.=20

Barnard found that 6 out = of 12=20 case-control studies and 5 out of 11correlation studies found = significant=20 associations between dairy intake and prostate cancer. Men with = the=20 highest levels of dairy intake were between 1.3 and 2.5 times more = likely=20 to get prostate cancer than those with the lowest consumption. = (link to article).

As with=20 breast cancer, increased IGF-1 levels from dairy may increase = prostate=20 cancer risk. In a 1998 study, men with the highest levels of IGF-1 = had=20 more than four times the risk of prostate cancer than men with the = lowest=20 levels of the growth factor. ("Plasma insulin-like growth factor-I = and=20 prostate cancer risk," Science, 1998)

Another=20 reason milk may be linked to prostate cancer is the calcium in the = milk --=20 the same calcium we're trying to get into our bones through our=20 diet. This calcium may decrease the body's supply of a form = of=20 vitamin D that helps to protect against prostate cancer, according = to a=20 2000 press release from the Harvard School of Public Health = ("Higher=20 Intake of Dairy Products May be Linked to Prostate Cancer Risk").=20

The press=20 release explains a study that found a moderately higher risk of = prostate=20 cancer from high dairy intake. The researchers also discovered = that men=20 who drank more that six glasses of milk each week had lower levels = of the=20 vitamin D that could protect against cancer than did men who drank = fewer=20 than two glasses.

__________

To comment = on this=20 article, contact astewart@consumerhealt= hjournal.com

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