Hypertension, insulin, and proinsulin in participants with impaired glucose tolerance

The association of insulin resistance and hyperinsulinemia to blood pressure has remained controversial. We examined the association of insulinemia to hypertension and blood pressure using baseline measurements for participants of the Diabetes Prevention Program (DPP). The DPP is a multicenter randomized controlled trial of 3819 participants with impaired glucose tolerance, and is designed to evaluate interventions for the delay or prevention of type 2 diabetes. The relationship between hypertension and insulinemia is described overall and by ethnicity. The effects of demographics (age and gender), adiposity, and glucose on the relationship are also presented. Asian Americans and African Americans had a similarly high prevalence of hypertension as did whites; American Indians had a lower prevalence of hypertension. Among participants not on antihypertensive medications, systolic blood pressure was significantly (but weakly) correlated with fasting insulin (r=0.12), homeostasis model assessment of insulin resistance (HOMA IR; r=0.13), and fasting proinsulin (r=0.10) when adjusted for age and gender (all, P<0.001). Systolic blood pressure showed similar correlations to fasting insulin in each ethnic group. After further adjustment for body mass index, the association of fasting insulin to systolic and diastolic blood pressures weakened considerably but remained significant (systolic: r=0.06, P=0.002; DBP: r=0.06, P<0.001). We conclude that a weak but significant association between insulin, (and proinsulin and HOMA IR) and blood pressure exists but is largely explained by overall adiposity. This association is similar among ethnicities, with the possible exception of Hispanics. The relation between insulin concentrations and blood pressure explains relatively little of the ethnic differences in hypertensive prevalence.