Influence of insulin, sympathetic nervous system activity, and obesity on blood pressure: The Normative Aging Study

Objective: To examine the association of insulin and sympathetic nervous system activity with blood pressure elevation in a cross-sectional study of 752 nondiabetic male participants of the Normative Aging Study, aged 43-90 years. Methods: Testing included a physical examination, medical history, fasting and post-carbohydrate insulin and glucose levels determinations, an anthropometric examination, and 24 h urine collection for catecholamine level determination. Total obesity was represented by body mass index, central obesity by the abdomen circumference:hip circumference ratio, and sympathetic nervous system activity by 24 h urinary excretion of norepinephrine. Results: Systolic and diastolic blood pressure (SBP and DBP, respectively) were positively related to body mass index, abdomen:hip ratio, norepinephrine excretion, and insulin levels in univariate analyses. The relationship between insulin level and SBP and DBP persisted after adjustment for body mass index, abdomen:hip ratio, norepinephrine, age, smoking, physical activity level, and antihypertensive medication use. The norepinephrine level was related to SBP and DBP after adjustment for insulin level, age, smoking, physical activity level, and antihypertensive medication use, and these relationships remained marginally significant after further adjustment for body mass index and abdomen:hip ratio. In contrast, neither body mass index nor abdomen:hip ratio were related to blood pressure after adjustment for insulin level. Among participants in the lowest tertiles both of insulin and of norepinephrine levels, 10% were hypertensive, compared with 35% in the highest tertiles of these variables. In a multiple logistic regression model, insulin level, norepinephrine level, and an interaction term for insulin level with norepinephrine excretion were independent predictors of hypertension Conclusions: The results suggest that insulin level and sympathetic nervous system activity are associated with hypertension among middle-aged and elderly men.