Different β-Casein Fractions in Icelandic Versus Scandinavian Cow's Milk May Influence Diabetogenicity of Cow's Milk in Infancy and Explain Low Incidence of Insulin-Dependent Diabetes Mellitus in Iceland

Abstract

Objectives. To compare children with insulin-dependent diabetes mellitus (IDDM) with controls in Iceland regarding their consumption of cow's milk in infancy, and to investigate the β-casein fractions in Scandinavian and Icelandic cow's milk. The A1 variant of β-casein has been shown to be diabetogenic in animal studies, and suggestions have been made that the B variant of β-casein acts similarly. Differences in the relative proportions of β-casein fractions might explain the lower incidence of IDDM in Iceland than in Scandinavia. Methods. A retrospective case–control study on IDDM patients and matching controls was performed in Iceland to compare their diets in infancy. Fifty-five children with IDDM born in Iceland over a 16-year period and randomly collected controls (n = 165) were recruited to the study. Mothers of the children answered questions on breastfeeding habits and on when cow's milk products were introduced. Samples of cow's milk from randomly selected milk batches from the largest consumption areas in Iceland and Scandinavia were collected. The milk samples were freeze-dried and their β-casein fractions were analyzed using capillary electrophoresis. Results. No significant difference was found between IDDM patients and controls in the frequency and duration of breastfeeding or the first introduction of cow's milk products. The analyses of milk samples showed that the percentage of the A1 and B variants of β-casein in Icelandic milk was significantly lower than in the milk from the Scandinavian countries. Conclusions. Cow's milk consumption in infancy is not related to IDDM in Iceland. The lower fraction of A1 and B β-caseins in Icelandic cow's milk may explain why there is a lower incidence of IDDM in Iceland than in Scandinavia.