Plasma cortisol levels increase with age in obese subjects

In order to assess the influence of age, sex, and body mass on plasma cortisol concentrations, we measured the 24-hour Integrated Concentration (IC) of cortisol (F) in 36 obese subjects (16 males, 20 females) aged 5.3-56.4 years, BMI = 35.5 +/- 7.3 kg/m2 and compared with 119 nonobese subjects, body mass indices (BMI) 21.2 +/- 2.7 kg/m2, aged 8.8-66.2 years (55 males, 64 females). Subjects were nondiabetic, normotensive, without history of psychiatric illness, and otherwise in good health. IC studies were performed using a continuous blood withdrawal methodology, and IC-F was assayed from the 24 hour pooled sample by a protein binding method. The effect of age and gender on IC-F was analyzed by multivariate regression. In the nonobese group there was no effect of age or sex on IC-cortisol levels, the mean IC-F = 173.8 +/- 44.1 nmol/L. A statistically significant but weak negative effect of BMI on IC-cortisol (r=-.18, p<0.05) was present. In the obese subjects there was a significant increase in IC-cortisol levels with age IC-F(nmol/L) = 2.76 x age(years) + 85.0 (r2=.36, p<0.0001). IC-cortisol levels tended to be lower in obese males than females when controlled for age (p<0.05). We conclude that in nonobese subjects IC-F levels are independent of age and gender. However, there is a significant increase of IC-cortisol levels with age in obese individuals. The observed increase of IC-cortisol with age may contribute to metabolic complications of obesity.