Modeling cortisol rhythms in a population-based study.

The aim of these analyses was to develop and describe easily implementable, yet information rich, approaches for analysis of the temporal profile of cortisol in human populations. A typical waking profile of cortisol in a sample of women aged 15-44 was parameterized by a piecewise linear regression model, implemented as a mixed model to accommodate repeated observations among individuals. The model was extended to distinguish characteristic cortisol profiles of obese women from those of non-obese women. Sharp inflection points for the diurnal profile of cortisol were noted at 30 and 75 min past awakening. Obese women showed a slight tendency to have a less sharply rising and declining response to awakening than non-obese women.