Hematocrit and the incidence of type 2 diabetes in the pima indians.

S everal prospective studies have shown that a high hematocrit (or hemoglobin) predicts type 2 diabetes (1–6). However, the reasons for this association have not been fully explored. Hematocrit has been positively correlated with hyperinsulinemia and conditions associated with insulin resistance such as high blood pressure, elevated serum triglycerides, low HDL cholesterol, and central obesity and could therefore be associated with insulin resistance (7,8). On the other hand, hematocrit is also a major determinant of blood viscosity (9). An elevated blood viscosity is thought to contribute to the development of insulin resistance by reducing blood flow to skeletal muscle, thereby interfering with insulin-mediated glucose uptake in this tissue (10). The aim of this study was to examine the association between hematocrit and type 2 diabetes incidence in the Pima Indians and to determine whether any association between hematocrit and diabetes incidence was altered by adjustment for fasting insulin.