Stress and exposure to elevated glucocorticoid (GC) levels cause changes in the hypothalamic-pituitary-adrenal (HPA) axis that affect cognitive and adaptive aging. Physiological responses to stress-including elevations in cortisol-are also moderated by individual differences in psychosocial and other biological factors. Identification of risk and protective factors associated with aging is a public health priority. Toward that end, we will examine HPA response to acute and sustained stressors, and its association with chronic stressors via salivary cortisol measures in the longitudinal assessment of a large sample of middle aged twins. Cognitive research on cortisol has focused on hippocampal dysfunction and episodic memory. However, there are disproportionate age-related abnormalities in prefrontal cortex and associated executive functions, and high concentrations of GC receptors in prefrontal cortex. We propose that cortisol-related cognitive dysfunction in aging will be associated with executive function as well as episodic memory deficits. We will also measure testosterone, DHEA, and genotype the GRK3 gene. Testosterone and DHEA decrease with age whereas cortisol tends to increase; even when cortisol does not increase with age, symptoms of hypercortisolemia may still be manifested. Thus, the ratio of cortisol to DHEA or testosterone (rather than absolute level of cortisol) may be a useful index of functionally elevated cortisol. GRK3 plays a role in regulating the CRF receptor; we will examine whether the P-5 variant of GRK3 is, associated with GC hypersecretion during stress and a lower threshold for stress-induced responses. The proposed study builds on our NIA-funded study, which we refer to as the Vietnam Era Twin Study of Aging (VETSA). The VETSA is assessing 720 twin pairs from the Vietnam Era Twin Registry (360 pairs at age 51+/-1; 360 pairs at age 56+/-1) with planned follow-up every 5 years. An extensive, daylong assessment includes neurocognitive, personality/psychosocial and health/medical measures, and blood samples for genotyping. Key advantages are beginning in midlife (before substantial age-related declines), and having only 2 large, narrow age cohorts to maximize power to detect within-person change over time. This study will begin in VETSA year 3 and include 480 VETSA twin pairs. We will compare at-home and in-lab cortisol, testosterone, and DHEA measures, thereby employing a relatively novel approach to provide comparison to typical (at-home) basal levels. Using multivariate twin analytic approaches, we will determine the extent of genetic, and shared and unique environmental factors influencing cortisol in midlife as well as their association with other key measures.
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