New York Times, May 30, 2006
RISE IN RATE OF TWIN BIRTHS MAY BE TIED TO DAIRY CASE
[Rachel's introduction: Monsanto has always claimed that its bovine growth hormone (known variously as rBGH, rBST and bovine somatotropin), injected into cows to make them give more milk, would have no effect on humans drinking the milk. Now a study indicates that women who drink Monsanto-modified milk (about 1/3 of all milk in the U.S.) are five times as likely to give birth to twins (compared to those drinking normal milk). Twin births can endanger the health of both the mother and the babies.]
By Nicholas Bakalar
American women who eat dairy products appear to be five times as likely to give birth to fraternal twins as those who do not, according to a new study, and one explanation may lie in dairy products from cows injected with synthetic growth hormone.
Dr. Gary Steinman, an assistant clinical professor of obstetrics at the Albert Einstein College of Medicine, reached that conclusion by looking at the medical records of 1,042 mothers who were vegans consuming no dairy products and comparing them with those of mothers who regularly ate dairy products.
His findings appear in the May issue of The Journal of Reproductive Medicine. Eating dairy products increases blood levels of insulinlike growth hormone, or I.G.F., and it is this increased hormone level that is associated with increased rates of multiple ovulation.
In a study published in 2000 and cited in the findings, vegan women had concentrations of I.G.F. that were 13 percent lower than those in women who regularly consumed dairy products.
Multiple births are associated with increased health risks for mothers and infants, but Dr. Steinman said he was not prepared to use these findings as the basis for advising women about diet before pregnancy.
"Since this is the first time diet has been implicated in an important role for determining twinning rate," Dr. Steinman said in an e-mail message, "it must be confirmed by others before rigid recommendations can be made concerning health care."
Insufficient diet in general lowers the rate of twin births, but Dr. Steinman said he had found evidence that the rate was directly related to levels of growth hormone.
"The more I.G.F., the more the ovary is stimulated to release additional eggs at ovulation," he said.
Animal studies, in rats and mice as well as in cattle, have convincingly demonstrated that increased serum levels of growth hormone are associated with increased ovulation.
All cow's milk has bovine growth hormone in it, naturally produced by the animal's pituitary gland. Many dairy farmers inject their cattle with recombinant bovine somatotropin, a synthetic version of the naturally occurring hormone. This increases size and milk production, but it has another effect: cows with higher growth hormone levels produce more twins.
The consumption of any dairy products increases blood levels of insulinlike growth hormone in humans, and consuming milk from cows that have been injected with synthetic growth hormone can have a correspondingly larger effect.
About one-third of American dairy cows are in herds where the hormone is used, said a spokesman for Monsanto, the only manufacturer of synthetic bovine growth hormone in the United States.
The evidence that eating dairy products increases the chances of multiple ovulation is suggestive, but not conclusive. Many factors, dietary and other, affect the rate of twin births. A study this month in Lancet, for example, suggests that the B vitamin folic acid may increase the survival of embryos in in vitro fertilization procedures, resulting in more twin births.
Fraternal twins run in families, so genetics also plays an important role. And the recent rise in the birth rate of twins is at least partly attributable to delayed childbearing, as older mothers are more likely to have twins.
The rate of twin births has also increased significantly since 1975, when assisted reproductive technology came into wide use. But these factors alone, Dr. Steinman said, do not explain the continuing increase in the rates in the United States since 1994, when recombinant bovine somatotropin was approved for sale.
In 2003, the United States had 3 sets of twins per 100 live births -- more than twice the rate of Britain, where growth hormone injection is banned. (Triplets and higher multiple births raise this figure to 3.18.)
Dr. Steinman suggested that one significant reason for the large difference was the recombinant bovine somatotropin.
"I am not claiming to be the first to show that variations in dietary amounts can affect the twinning rate," Dr. Steinman said. "What is new is specifying what in the diet may have this effect and how."
Copyright 2006 The New York Times Company