The controversial link between drinking cows' milk during infancy and the risk of developing diabetes may have been strengthened by a new study that finds that exposure early in life to cow's milk may increase the lifetime risk of developing diabetes in high risk children.
In children diagnosed at a young age with diabetes, insulin autoantibodies are particularly present and are believed by some researchers to be the primary event in the process leading to type 1 diabetes.
Exposure to cows' milk has previously been shown to cause the body to mount an immune response to insulin in some children and may precipitate the development of these autoantibodies, but the link has been disputed by at least one major study.
In the current study Dr Johanna Paronen from University of Helsinki, Finland, and colleagues studied infants with relatives who had diabetes. The authors analysed the development of insulin specific T cell responses, the emergence of insulin binding antibodies by enzyme immunoassay, as well as the development of insulin autoantibodies by radioimmunoassay, in relation to exposure to cows' milk and family history of type 1 diabetes.
All the infants included in the study had a first degree relative with type 1 diabetes and therefore were at an increased genetic risk of developing the disease (Diabetes 2000;49:1657-65).
The infants were randomised to receive either cows' milk or a non-cows' milk hydrolysed casein based formula while also being breast fed for the first 6 to 8 months of life. According to the protocol, all infants were supposed to receive either cows' milk or formula for a minimum of two months.
Breast feeding was encouraged, and the mothers were asked to add cows' milk or formula to their infant's diet at age 6 months at the latest, although most infants included in the study had received supplementation much earlier.
After correcting for differences in the timing of the introduction of supplemental milk between the randomisation groups, researchers found that at the age of 3 months, both cellular and humoral responses to bovine insulin were higher in infants exposed to cows' milk than in infants fully breast fed. IgG antibodies to bovine insulin were also higher in infants who received cows' milk than in infants who received the formula at 3 months of age.
Additionally, these responses were also higher for those receiving cows' milk than for 14 infants whose mothers decided to continue exclusive breast feeding past 8 months, therefore never adding cows' milk or formula to their baby's diet.
The results show that at 3 months of age, infants who had been fed cows' milk had a significantly higher immune response to bovine insulin than did infants who received the other formula or were breast fed, the authors reported. The groups showed no differences, however, in reactivity to human insulin at that age.
"Our observations raise the issue of whether oral exposure to foreign insulin plays a role in the autoimmune process leading to type 1 diabetes," Dr Paronen and colleagues wrote. It could be that in some predisposed children, early exposure to cows' milk could trigger an immune reaction to insulin.
"The initiation of insulin-specific T-cells by dietary insulin in the gut immune system may carry a risk for an autoimmune process progressing ultimately to clinical type 1 diabetes," they concluded.