Identifying patterns in cortisol secretion in an older population. Findings from the Whitehall II study.

Alterations in the patterning of diurnal cortisol secretion are associated with poor health in clinical populations with 'flat' patterns a particular risk. Flatter patterns in cortisol secretion may reflect impaired negative feedback in the hypothalamic-pituitary-adrenal axis. The correlates of discrete clusters of patterns in the diurnal secretion of cortisol have not been well described in large community dwelling populations. We describe discrete clusters of patterns of cortisol secretion and examine the correlates of these patterns using a latent variable mixture modelling approach. Analyses use data from 2802 participants with complete information on cortisol secretion, age, walking/gait speed, stress, waking up time and sleep duration. Cortisol was assessed from six saliva samples collected at waking, waking plus 30 min, 2.5h, 8h, 12h and bedtime. We find two patterns ("curves") of diurnal cortisol secretion. These curves are described as 'normative' [prevalence 73%] and a 'raised' [27%] curve differentiated by a lower cortisol awakening response in the normative group, a higher diurnal cortisol and 'flatter' pattern of release in the raised group. Older age, being male, a smoker, stress on the day of sampling, slower walking speed and shorter sleep duration increased the odds of being in the raised curve, relative to the normative curve. In conclusion, two patterns of cortisol secretion occur in middle aged men and women. Raised pattern of secretion, which occurs in 27% of our participants is associated with demographic variables, adverse health behaviours, psychosocial environment and impaired physical functioning.