Synthetic Hormone In
Milk Raises New Concerns
By Susan Gilbert
NY Times
It was the confluence of two important events that made Carol Baxter start buying organic milk about five and a half years ago. Her oldest daughter had just turned 1 and soon would move from breast milk to cow's milk. And American dairy farmers had just received approval to inject their cows with recombinant bovine growth hormone, a genetically engineered hormone that increases milk production.
Ms. Baxter, who lives in Palisades, N.Y., knew of environmental groups' claims that treated cows got more infections and needed more antibiotics, which could then enter their milk. And she learned that some scientists had raised the possibility of an increased cancer risk in people who drank the milk. "Milk is such an important part of a child's diet," she said. "I didn't want my child to be a guinea pig."
The Food and Drug Administration has long dismissed such concerns. In the journal Science in 1990, two agency scientists concluded that "no toxicologically significant changes" were seen in rats that ingested the hormone. The agency's approval of the hormone in 1993 rested on the strength of that 90-day rat study, which was commissioned by Monsanto, the manufacturer.
Safety questions about the hormone never went away among health-conscious consumers, and recently the old questions have resurfaced in light of new research and a fresh examination of the rat study.
Last week, the Canadian government said that it would not approve the synthetic hormone. Canadian scientists reviewed unpublished data from the study and found health effects that had not been cited in the Science report. Canada's decision leaves the United States the only major country to permit use of the synthetic hormone.
In its analysis of the Monsanto rat study, the Canadian scientists found that 20 percent to 30 percent of the rats that ingested high doses of the hormone developed antibodies to it, a sign that it was active in the bloodstream. And some of the male rats developed cysts on their thyroids and abnormalities in their prostates.
In December, after the Canadian researchers released their findings, Sens. Patrick Leahy and James Jeffords, both of Vermont, asked Health and Human Services Secretary Donna Shalala to investigate whether the =46DA overlooked evidence in the case. Dr. Shalala has not yet responded.
In addition, in December, 21 dairy farmer associations and consumer groups in the United States said they would file suit against the FDA for failing to require additional safety studies of the hormone. "The 90-day rat study doesn't show that recombinant bovine growth hormone is a human health hazard," said Dr. Michael Hanson, a research associate for the Consumer Policy Research Institute, a division of the Consumers Union, one of the groups. "But neither does it show that there is no possibility of any health hazard, as FDA claimed. It's clear that FDA has grossly misled us."
The agency is writing a response to the concerns, said Dr. Stephen Sundlof, director of its Center for Veterinary Medicine. He acknowledged that the agency had not reviewed the antibody data in the approval process "for reasons I can't explain."
He said the agency had seen the information on the thyroid and prostate effects, but considered them "biologically meaningless" because they were no more prevalent in rats fed high doses of the hormone than in those fed low doses. Ordinarily, if a substance like a drug affects the body, the effects increase as the dose increases. "Consumers have no reason to be concerned about the milk," he said.
Monsanto said its product, called Posilac, is safe. Extensive evaluations have established that the hormone supplements for cows do not change the composition and wholesomeness of milk, Dr. David Kowalczyk and Dr. Robert Collier, Monsanto scientists, wrote in a statement released Jan. 12. The scientists point out that the United Nations Joint Expert Committee on Food Additives, which determines the safety of residues from veterinary drugs in foods, affirmed in March that the growth hormone was safe.
Besides the Canadian investigation, two studies published last year rekindled longstanding worries about a possible increased risk of cancer from consuming milk from hormone-treated cows. Reports from two continuing Harvard-based studies, the Physicians' Health Study and the Nurses' Health Study, found that insulin-dependent growth factor 1, a protein that is elevated in the milk of hormone-treated cows, is a strong risk factor for breast cancer and prostate cancer.
Researchers in the study say this protein circulates naturally in the human body at such high levels that the added amount in treated milk is unlikely to be noticed. Also, it occurs in breast milk in higher amounts than in the milk of hormone-treated cows. And, the researchers say there is no evidence that consuming the substance in food contributes to cancer risk.
Last January, scientists with the Physicians' Health Study reported in Science that men with the highest levels of IGF-1 in their blood were four times as likely to develop prostate cancer as men with the lowest levels. In May, scientists with the Nurses' Health study reported in The Lancet that premenopausal women with high levels of IGF-1 had up to a seven-fold increase in breast cancer risk over those with low levels. They said the findings suggest "that the relation between IGF-1 and risk of breast cancer may be greater than that of other established breast-cancer risk factors," except for family history and dense breast tissue.
Dr. Michael Pollack, who was involved with both studies, noted that the difference between the IGF-1 in milk from untreated cows and treated cows is relatively small. Levels range from 1 to 9 nanograms per milliliter of milk from untreated cows and 1 to 13 nanograms per milliliter of milk from treated cows, the FDA said. And because levels in human milk are slightly higher, "if there's a biological difference, one would be most concerned with human milk," said Pollack, a professor of medicine and oncology at McGill University
He said that, according to Canadian scientists, the amount of IGF-1 that people consume in cow's milk is less than 1 percent of the total amount of IGF-1 that naturally circulates in the body, regardless of what people eat.
Still, he said he could not rule out the possibility that daily exposure to the small additional amounts of IGF-1 in milk over a lifetime could increase a person's cancer risk. "It's a hypothetical concern," he said.
=46or one thing, scientists cannot tease out the human health risk of IGF-1 from foods until they know how much of it remains active in the body after digestion. But that point is also in dispute.
"When you consume any peptide, like IGF-1, very little of it is absorbed in an active form," said Dr. Carolyn Bondy, chief of the developmental endocrinology branch of the National Institute of Child Health and Human Development. Dr. Bondy's research found a connection between abnormal mammary gland growth in female monkeys and high levels of IGH-1 given to the monkeys, but these IGF-1 levels were far greater than people get from drinking milk, she said.
Even though the increased amount of IGF-1 in treated milk is small, Hanson said the possible health effects could not be dismissed. He cited a 1995 study in the Journal of Endocrinology showing that the breakdown of IGF-1 in rats is slowed in the presence of casein, a protein in milk. "If casein increases the half life of IGF-1, the effects could be dramatic," he said.
Several experts agree with the Consumers Union and the other parties in the planned lawsuit against the FDA that more testing is needed to establish whether bovine growth hormone supplementation is safe. "More studies need to be done," said Dr. Marion Nestle, director of the department of nutrition at New York University, who opposed the approval of the hormone as a representative on the drug agency's advisory panel that approved it.
"The science on the effects of oral ingestion of IGF-1 is incomplete," the American Medical Association said in a statement last month, in response to a reporter's questions.
In the climate of uncertainty, one thing is for sure. Many consumers want milk without added hormones and antibiotics. Sales of organic milk nearly doubled to almost $31 billion in 1997, from about $16 million in 1996, according to dairy industry figures.
And Wendy Gordon, executive director of Mothers and Others for a Livable Planet, said demand was strong for its list of milk manufacturers, organic and nonorganic, whose dairies pledge not to use the synthetic hormone.