Hostility and urine norepinephrine interact to predict insulin resistance: The VA normative aging study

OBJECTIVE: Previous research has produced mixed results pertaining to the association between hostility and insulin resistance. These inconsistent findings may be the result of a lack of studies examining potential moderators of this relationship and inconsistent measures of insulin resistance and/or hostility. We hypothesized that hostility may interact with circulating norepinephrine (NEPI) levels, indexed by 24-hour urine concentrations, to affect insulin resistance. METHODS: Six hundred forty-three men (mean age = 63.1 years) free of diabetic medications completed the Minnesota Multiphasic Personality Inventory and participated in a laboratory assessment. The Cook-Medley Hostility (Ho) and 24-hour urine NEPI were used to predict insulin resistance defined by the homeostatic model assessment (HOMA) index, 2-hour postchallenge glucose (PCGL), and insulin levels (PCIL) after controlling for nine common covariates. RESULTS: Multiple regression showed that the two-way interaction between Ho and NEPI significantly predicted HOMA and PCIL, but not PCGL, after controlling for covariates. Simple regression slopes of Ho on HOMA and PCIL were explored and indicated that, at higher levels of NEPI, higher Ho was associated with higher HOMA (β = 0.14, p < .05). Ho was not a significant predictor of HOMA at mean and lower levels of NEPI. Similar results were obtained for PCIL, but not PCGL. Cynicism, but not other subscales of Ho, was similarly related to insulin resistance and NEPI. CONCLUSION: Individuals with high stress and high hostility were more likely to have insulin resistance. It is important to study moderators in the relationship between hostility and insulin resistance.