Effects of Major Depression, Aging and Gender upon Calculated Diurnal Free Plasma Cortisol Concentrations: a Re-Evaluation Study

Abstract

Depression, aging and female gender are associated with increased diurnal concentrations of total plasma cortisol. For the physical effects of hypercortisolemia, however, it is generally assumed that free rather than total plasma cortisol concentrations are of importance. Herein, we report a mathematical approach to determine free plasma cortisol concentrations on the basis of total cortisol, corticosteroid binding-globulin (CBG) and albumin plasma concentrations. This approach was used to re-evaluate two sets of data in order to estimate the effect of depression as well as the effect of aging and gender upon free plasma cortisol concentrations. Comparing male depressed patients with healthy controls, we found 24-hour free cortisol minima (MIN: 4.1 ± 1.8 vs. 1.6 ± 1.1 nmol/l, p < 0.0001), mean (MEAN: 25.5 ± 6.7 vs. 10.4 ± 2.7 nmol/l, p < 0.0001) and maximal (MAX: 85.3 ± 23.3 vs. 45.2 ± 15.8 nmol/l, p < 0.0001) concentrations to be significantly increased in depressed patients. In general, the impact of depression upon total plasma cortisol were not only maintained, but stronger regarding free plasma cortisol. Also, age was associated with free plasma cortisol MIN (F1.30= 10.8, p < 0.003) and free plasma cortisol MEAN (F1.30 = 8.9, p < 0.006). All effects of age upon total plasma cortisol were generally also found in free plasma cortisol, though with less impact. No effect of gender upon any of the given free plasma cortisol outcome variables was found. Taken together, our re-evalution clearly shows not only depression but also aging to be associated with increases in free plasma cortisol concentrations. This finding is in line with the observation that in both conditions medical problems triggered and/or maintained by glucocorticoids (e.g. osteoporosis) are frequently seen.