Two new studies have confirmed the theory that drinking cow's milk as an infant raises a person's risk of developing diabetes.
Coming on the heels of an analysis of 20 other studies that reached the same conclusion, the suspected link now is "very solid," says Dr. Hans-Michael Dosch, a professor of pediatrics and immunology at the Hospital for Sick Children in Toronto.
"We recommend that if at all possible, breast-feeding in the first three or four months is the best thing you can do for your baby," Dr. Dosch says. "Most of the increased risk of developing diabetes due to cow's milk is restricted to the first three to four months of life."
Dr. Dosch published a study two years ago showing that bovine serum albumin, a protein in cow's milk, closely resembles a protein that sits on the surface of insulin-producing cells in the pancreas.
The resemblance is so close, in fact, that the result is a case of mistaken identity on the molecular level -- the body's infection-fighting immune system is tricked into thinking that the cells on the pancreas are actually foreign tissue.
Dr. Dosch has theorized that the mistaken identity prompts the body to mount an immune attack to destroy the proteins, in the process destroying the insulin-producing cells and turning the person into a diabetic.
The new studies, both published in this month's issue of the journal Diabetes Care, confirm that infants who consume cow's milk are at increased risk of developing diabetes.
In the first study, researchers from Australia and Colorado examined about 90 percent of all children who developed insulin-dependent diabetes in New South Wales, Australia, over an 18-month period in 1990 and 1991. Each child was compared to two healthy children of the same sex and age.
Those who were exclusively breast-fed during their first three months of life had a 34 percent lower risk of developing diabetes than those who were not breast-fed, the study found. Children who were given cow's milk-based formula in their first three months of life were 52 percent more likely to develop the disease than those not given cow's-milk formula.
The study also found that children who had developed an infection after age 9 were nearly three times more likely to become diabetic than children who had not developed any infection.
Attending day care before age 3, and drinking a lot of cow's milk after age 9, also appeared to increase the risk of developing diabetes.
While the increases in risk may sound high, the risk remains exceedingly low. On average, insulin- dependent diabetes affects fewer than one in 250 people in the United States. Even at that, most people born in the United States since the 1940s have been fed cow's milk-based formula before they were 3 months old.
Even for family members of people with diabetes, the risk of developing the disease is quite low. If a mother has insulin-dependent diabetes, her baby's risk of developing it is only about 1 percent. If a father has it, the baby's risk is still only 6 percent to 9 percent. If one identical twin develops it, the risk that the other twin will also develop it is still only about 30 percent.
Dr. Dosch agreed that because the risk of developing diabetes is generally quite low, it would not make sense to avoid feeding an infant with a cow's milk-based formula merely to prevent diabetes. But for many other health benefits, breast-feeding is .. widely recommended as the preferred way to feed a newborn, he said.
For mothers who are unable to breast-feed, infant formulas are available that do not seem to raise the risk of developing diabetes, Dr. Dosch says. In studies on animals, Nutramigen, a formula specially made by Mead-Johnson for infants with allergies, protects against the risk of developing diabetes, he says.
But it and similar specialty formulas are more expensive than FTC ordinary formulas, he adds.
The other new study, led by researchers at the University of Rome, compared the risk of diabetes in nine regions of Italy based on the consumption of milk by children in those regions.
The study found an almost perfect fit between how much milk the children in each region drank and how high their risk of developing diabetes was. Statistically speaking, milk consumption and the incidence of diabetes was 84 percent correlated.
"It's amazing," Dr. Dosch says. "I was surprised that there is such a clear-cut effect in one country. It suggests a closer correlation than we had previously assumed."
While the risk associated with cow's milk-based formula is relatively low in any individual child, on a society-wide basis there may be great benefit from eliminating bovine milk albumin from an infant's diet, Dr. Dosch says. Some dairy producers are already trying to develop a way to eliminate it from milk, he adds.