Does Cow's Milk Cause Early Puberty?

Au Pairs and Nannies Can Serve More Than Just Organic Milk

A debate has been raging for years over whether girls are now reaching puberty earlier than ever before. The debate escalated in 1997, when the journal Pediatrics published a study of 17,000 girls by Dr. Marcia Herman-Giddens of the University of North Carolina that found outward signs of puberty that precede menstruation — budding breasts and pubic hair — were hitting younger. Now scientists are trying to unravel why.

Nannies, au pairs, and mothers constantly say that cow's milk is to blame. This theory that hormones (steroids) in cows milk causes early puberty is merely hypothesized, but not proven. (Not that someday it might be clinically studied and proven).

In fact, the man-made bovine growth hormone that is blamed on early development in girls does not survive pasteurization. That's right. The steroid is destroyed before children drink the milk!

Plus, the Food and Drug Administration (FDA) scientists have concluded that eating foods with slightly higher levels of rbGH does not affect human health. This is because the amount of rbGH that is in milk or milk products as a result of treatment of the animals is insignificant compared to the amount of growth hormone that is naturally produced by our bodies.

Also, rbGH is a protein hormone and is digested into smaller fragments (peptides and amino acids) when eaten.

The rbGH hormone used on dairy cattle is effective in promoting growth in cows, but does not work in humans. Scientists know that rbGH is not recognized as a hormone by human cells.

Some speculate that good nutrition may lead to early puberty. Others speculate chemicals in plastics could cause early breast development.

But, so far the only cause that has been proven is that high mass body weight produces more estrogen causing overweight girls to start puberty earlier than other girls.

The reason that fat is the top theory is that the fatter you are, the more your body can convert adrenal hormones into the female sex hormone estrogen.

Overweight children's blood harbors more insulin, which also influences maturation.

Scientists even are studying whether the protein leptin, produced by fat cells, influences glands that produce sex-related hormones. See "Fat cell metabolism in different regions in women. Effect of menstrual cycle, pregnancy, and lactation," by M Rebuffe-Scrive in The Journal of Clinical Investigation.

"It does not mean that every overweight girl is going to enter puberty earlier, but on average they do," says Herman-Giddens, the study's author and child health specialist.

"It has been long known that if you are overweight as you grow up, you are more likely to begin puberty early," said Aviva Must, Ph.D., associate professor of Public Health and Family Medicine at Tufts University School of Medicine in Boston and lead author of the study, published in the September issue of the journal of Pediatrics. "Girls who are overweight are more likely to have early menarche, or start their period, before age 12."

But Dr. Must also explains that although overweight girls are more likely to start their periods earlier than their peers who are at or below normal weight, early menstruation is not by itself a risk factor for later obesity, according to the study.

Elizabeth Chang, staff writer for the Washington Post, wrote in her Oct. 7, 2003 article "Tempest in a Glass: Synthetic Hormones in Milk Don't Speed Puberty, Say Experts:"

"Could hormones meant to make cows give more milk lead to early puberty, as some parents fear? On its face, it sounds plausible enough. But government and pediatric health experts say there are no scientific data to back up such an assertion. For one thing, they say, rBGH [man-made bovine growth hormone] does not survive pasteurization. And even if it did, they add, it has absolutely no effect on human growth...

For years, pediatricians have viewed age 11 as the mean age of breast development... In 1997 a landmark analysis of 17,000 U.s. girls led by University of North Carolina professor Marcia Herman-Giddens showed that many American girls were beginning to show secondary sexual characteristics between ages 9 and 10... But the changes documented in Herman-Giddens's study cannot be attributed, even in part, to artificial bovine growth hormone for one important reason: The data for her study were collected in 1992 and 1993, before rBGH was available for dairy herds in the United States. Another problem with the rBGH and early puberty theory: Children today drink markedly less milk than they did a generation or two ago."

The American Council on Science and Health stated in their June 2001 publication "The Role of Milk in Your Diet:"

"Experts aren't sure whether girls really are entering puberty earlier. If they are, the most likely explanation is that today's girls are heavier than their mothers were at the same age. Puberty tends to occur earlier in heavier girls.

There is no research demonstrating that milk or dairy products play a role in early puberty. Milk has always contained hormones in very small amounts; their presence is not a result of any changes in animal husbandry practices. Today's girls drink less milk than their mothers did. Thus, it seems very unlikely that milk is responsible for any change in the age at which girls enter puberty."

The benefits of drinking milk far outweigh the risks. Although there have been no clinical studies proving that cow's milk encourages early puberty in girls, the fact remains future studies may. Plus, serving children organic milk certainly does not hurt them. Nannies, au pairs, and parents do not need to be scared to serve children cow's milk.

Do you serve children only organic milk?