Impact of Age on Cortisol Secretory Dynamics Basally and as Driven by Nutrient-Withdrawal Stress*

The present study tests the clinical hypothesis that aging impairs homeostatic adaptations of cortisol secretion to stress. To this end, we implemented a short-term 3.5-day fast as an ethically acceptable metabolic stressor in eight young (ages 18–35 yr) and eight older (ages 60–72 yr) healthy men. Volunteers were studied in randomly ordered fed vs. fasting sessions. To capture the more complex dynamics of cortisol’s feedback control, blood was sampled every 10 min for 24 h for later RIA of serum cortisol concentrations and quantitation of the pulsatile, entropic, and 24-h rhythmic modes of cortisol release using deconvolution analysis, the approximate entropy statistic, and cosine regression, respectively. The stress of fasting elevated the mean (24-h) serum cortisol concentration equivalently in the two age cohorts [i.e. from 7.2± 0.35 to 11.6 ± 0.71 μg/dL in young men and from 7.7 ± 0.39 to 12.6 ± 0.59 μg/dL in older individuals (P < 10−7)]. The rise in integrated cortisol output was driven mechanistic...