The SF-36 component summary scales and the daytime diurnal cortisol profile

Higher daytime cortisol output has been associated with higher levels of perceived stress and worse mental and physical health outcomes. Hypothalamic-pituitary-adrenal (HPA) axis dysregulation, such as elevated secretion of daytime cortisol, occurs in many mental and physical illnesses. However, the nature of the association between functional health status and daytime cortisol production has not been established.

Healthy adult volunteers (n=68, 45 females) provided saliva samples 3, 6, 9 and 12 h after waking, for two consecutive days, in everyday settings. Bivariate correlations between log salivary cortisol concentrations were calculated, and the SF-36 component summary scores were calculated. Latent growth curve modeling was used to model the daytime profile and adjust for covariates (age, sex and waking time).

Higher PCS scores were not associated with cortisol three hours after waking (cortisol intercept), or the diurnal decline (cortisol slope). Higher MCS scores were correlated with faster cortisol decline across the day (r=-.31, P<.01) but not with cortisol intercepts. In a latent growth curve model adjusting for age, sex and waking time, the association was no longer statistically significant.

Large scale epidemiological studies involving salivary cortisol would benefit from measuring SF-36 component summary scores. Cortisol intercepts and slopes may be differentially related to the PCS and MCS, although greater statistical power is needed to test this hypothesis more fully. Associations between daytime cortisol and the PCS or MCS could reflect the regulatory competence of bodily systems, common causes or unmeasured confounding factors.