The Weekly Newsmagazine of Science
Volume 155, Number 26 (June 26, 1999)
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By N. Seppa
Many studies have linked cows' milk consumed by babies to subsequent diabetes, but some researchers still doubt that it causes the disease. The association is based on animal experiments, they note, or indirect evidence (SN: 10/19/96, p. 249), such as studies in which parents of diabetic children try to recollect when their babies first started drinking milk-based formula.
Now, Finnish researchers have avoided the vagaries of poor recall by studying children from birth. In so doing, they have added to the case against cows' milk.
By monitoring babies in diabetes-prone families, the scientists find that infants getting formula that includes cows' milk are more likely later to develop the immune reactions associated with juvenile-onset, or type I, diabetes than are babies getting a substitute. The scientists reported the findings this week in San Diego at the 59th Annual Scientific Sessions of the American Diabetes Association.
The researchers tracked, until age 8 months, 173 newborns in Finland who had a close relative with type I diabetes. To augment their mothers' milk, half of these babies received milk-based formula and the rest got a formula in which the cows' milk proteins had been broken into fragments called peptides. The two formulas taste and smell the same, so parents and researchers didn't know which one a baby was drinking.
Babies' immune systems largely ignore cows' milk proteins that have been chopped up. However, contact with one intact protein in cows' milk, bovine insulin, may set off a destructive process, suggest immunologist Outi Vaarala and her colleagues at the University of Helsinki. The immune system would attack pancreas islet cells that make human insulin, which resembles bovine insulin, and would produce antibodies.
At 2 years of age, 10 of 89 children getting cows' milk formula had formed antibodies associated with type I diabetes. However, only 3 of 84 babies receiving the treated milk showed these antibodies, says Hans K. Akerblom, a pediatrician at the University of Helsinki.
These autoimmune antibodies, or autoantibodies, are made by immune B cells and appear to dispose of damaged pancreatic islet cells, says Hans-Michael Dosch, an immunologist at the Hospital for Sick Children in Toronto. The antibodies indicate that bovine insulin might be spurring an immune system T-cell reaction against the child's own islet cells, he says. Insulin regulates sugar metabolism in the body.
Research had already determined that having one type of autoantibody to insulin indicates that a baby has roughly a 4 in 10 chance of contracting type I diabetes within the next decade, says study coauthor Suvi M. Virtanen, a nutritional epidemiologist at the University of Tampere in Finland. Having more types of these autoantibodies is a sign of greater risk; having three imparts an 80 to 90 percent likelihood of getting type I diabetes. In this study, 3 of the 10 children in the cows' milk group who had diabetes-related autoantibodies showed one type of such antibody, and the rest had two or more.
The precise cause of diabetes remains unclear. The children in the study were genetically predisposed to it, but most will never get the disease. Something in the environment or diet may trigger it.
Some researchers suggest that changing a predisposed child's diet might derail the disease. However, the proteins and calcium in cows' milk impart great benefits, Akerblom says. "None of this [research] is strong enough ... to start changing habits about how mothers raise children," he warns.
Dosch agrees but notes that the evidence against cows' milk is piling up. As an example, he cites research from Puerto Rico. There, fewer than 5 percent of mothers breast-feed their children. Instead, nearly all use formula made from cows' milk. Meanwhile, type I diabetes incidence in Puerto Rico is roughly 10 times the rate seen in Cuba, where breast-feeding is nearly universal.
Such findings suggest that the problem may be cows' milk ingested in the first few months of life. After all, Dosch says, "we are the only species that drinks another species' milk. It's a weird thing. We have not evolved to be exposed to [bovine insulin] protein."
From Science News, Vol. 155, No. 26, June 26, 1999, p. 404. Copyright © 1999, Science Service.
Copyright © 1999 Science Service