Psychosocial environment and health: methodological variability of the salivary cortisol measurements

Salivary cortisol offers a novel approach to understand the relationship between psychosocial environment and health. This study examines the intra-individual relationships among indicators of the cortisol circadian rhythm and investigates the influence of determinants affecting the day-to-day variability of the cortisol measures. Over three weekdays, 87 healthy subjects (63 females and 24 males) collected saliva samples at seven time points to assess the cortisol awakening response (CAR), and to evaluate the post morning cortisol profile. The generalized estimating equations method was used to explore the relations between repeated cortisol measures and potential determinants (sociodemographic, health, and sampling factors) influencing salivary cortisol levels. Younger age, being smoker, and sampling on a working day were associated with higher at awakening and total cortisol excretion in the morning period. Higher overall cortisol excretion and cortisol increase in the first hour of the day were found for adherents to sampling procedure. Higher educational level was found associated with greater total cortisol excretion in the morning and post morning period, while a flatter diurnal slope was found in smokers. Results are consistent with the knowledge that the circadian cortisol rhythm is differentially determined by situational factors and that results obtained in the early morning hour are of crucial importance corroborating the evidence that the CAR is a highly state-dependent phenomenon. These data indicate that many confounding factors need to be controlled when using salivary cortisol as biomarker of the mind-health interrelationship.