The epidemiology of diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) develops predominantly in childr en and young adults, bur may appear in all age groups. The incidence of IDD M differs greatly among populations, with Finland and Sardinia showing the greatest incidence rates (similar to 30-35% of cases annually per 100000 ch ildren up to age 14 years) and oriental populations showing the lowest rate s. IDDM is diagnosed more frequently in the winter months. The major geneti c susceptibility to IDDM is linked to the HLA complex on chromosome 6. Thes e genetic backgrounds interact with environmental factors (possibly certain viruses, foods and climate) to initiate the immune-mediated process that l eads to beta-cell destruction. Non-insulin dependent diabetes (NIDDM) is the most common form of diabetes. The prevalence of NIDDM varies enormously from population to population. T he greatest rates have been found in Pima Indians. The major environmental factors identified as contributing to this form of diabetes are obesity and reduced physical activity. NIDDM shows strong familial aggregation in all populations and is clearly the result of an interaction between genetic sus ceptibility and environmental factors. Before NIDDM develops, insulin conce ntrations are high for the degree of glycaemia and of obesity, reflecting t he presence of insulin resistance. As insulin resistance worsens, glucose l evels increase, with the appearance of glucose intolerance and, finally, of NIDDM, when insulin response cannot compensate for insulin resistance.