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More research suggests that certain children may be vulnerable to diabetes later in life after exposure to cow's milk while very young.
The Finnish study looked at children who already have one close relative with type I diabetes.
Previous research has suggested that children exposed to the insulin which can naturally be contained in cow's milk may develop antibodies to insulin.
Insulin is the naturally-produced chemical which helps animals, including humans, reduce excess levels of blood sugar.
Diabetics either have lost the ability to produce their own insulin, or have developed bodies on which insulin has too little effect.
How children lose the ability to produce their own insulin - rendering them reliant on injections for life - is still a matter of much debate among doctors.
It is believed that the body's own immune system suddenly turns on the cells in the pancreas gland which produce the chemical, destroying them, but what makes them decide to attack is unknown.
Dr Johanna Paronen from the University of Helsinki looked at "high risk" infants who had been either given formula feed with cow's milk since birth, or given a combination of breast feeding and non-bovine formula.
At three months old, those given cow's milk had immune systems which reacted far more strongly to bovine insulin.
The levels of immune system antibodies to bovine insulin and human insulin tended to be higher in the group of infants fed only cow's milk.
The researchers wrote: "Our observations raise the issue of whether oral exposure to foreign insulin plays a role in the autoimmune process leading to type I diabetes.
"It is possible that in some genetically susceptible children, a continuous, even small-dose early exposure to bovine insulin in cow's milk may lead to loss of tolerance to insulin."
Interestingly, where the child had a diabetic mother, rather than a diabetic father, this effect was less marked.
The researchers suggested that exposure pre-natally to both diabetes, and any insulin treatment, might decrease the risk.
However, a spokesman for Diabetes UK said: "Various research studies have looked into the theoretical link between drinking cow's milk and the onset of Type 1 diabetes.
"Whilst some evidence appears to support the theory it is not conclusive, and there is just as much evidence against the theory."
She added that while breast feeding was to be recommended in general, there was not enough evidence for women who could not breast feed to stop using formula feeds and cow's milk.