Cortisol secretion in saliva and hair: methodological considerations and relationships with state and trait well-being
Cortisol secretion follows a distinct circadian rhythm characterised by a nadir in early sleep, gradually increasing concentrations during late sleep, peak levels at 30-45 minutes post awakening (the cortisol awakening response: CAR) and a declining pattern thereafter. Salivary cortisol enables determination of the diurnal pattern within the domestic setting, although the measurement presents methodological challenges that need to be addressed. Further, the diurnal pattern of cortisol has been studied in relation to trait and state ill-being, rather than well-being. Consequently the focus of this programme of research was to explore relationships between the diurnal pattern of cortisol secretion and measures of both state and trait well-being and to examine the impact of electronically determined participant adherence to protocol within the domestic setting. In the first instance healthy, psychopathology-free young females were investigated but the work was extended to investigate the impact of aging on associations between cortisol secretion and well-being in healthy older females. Data from healthy female participants demonstrates for the first time that moderate delays (on average 8 minutes) between awakening and the start of saliva sampling (previously considered tolerable) result in erroneous over-estimation of CAR magnitude and earlier timing of the CAR peak. This minimal level of non-adherence was not detected by self-reported awakening time, suggesting that electronic monitoring of awakening is essential in CAR research. The effects of moderate delays on the CAR measurement were explored in a detailed study, the first to sample salivary cortisol secretion at five minute intervals in the immediate post-awakening period. Over-estimation of the CAR magnitude and earlier peak were attributed to an observed approximate ten minute time lag between awakening and the start of the cortisol rise. In contrast non-adherence to the sampling protocol across the day did not impact on measurement of the diurnal cortisol measures when measured at 3-12 hours post-awakening. In healthy young females neither state nor trait well-being/ill-being were associated with the CAR when using data strictly monitored for non-adherence during saliva sampling in the post-awakening period. Additionally, state and trait well-being were not associated with the diurnal decline or mean levels of cortisol across the day. These null findings could be attributed to the age of the sample. Previous associations between well-being and diurnal cortisol patterns have been observed mostly in middle-aged and older adults. The new method of cortisol assessment in hair samples provided a retrospective trait measure of cortisol secretion, without the problems of non-adherence to protocol. No associations between three months hair cortisol secretion with well-being/ill-being were observed in young healthy females, in line with the results reported above using salivary cortisol. However, in the older sample associations between hair cortisol and trait well-being were evident. Higher levels of trait well-being were associated with higher hair cortisol, independently of ill-being, providing support for cortisol as an ‘energiser’ in healthy older female participants. Together these findings provide evidence for the neurotoxicity hypothesis of cortisol secretion; well-being did not exert effects on cortisol secretion in early adulthood but effects were evident in late adulthood in healthy psychopathology-free female samples. The unique contribution of this programme of research lies in its consideration of methodological issues in the measurement of cortisol and well-being and its focus on positive psychology rather than the traditional psychopathology in relation to cortisol.
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