Salivary Morning Cortisol and Sleep Quality in Healthy Subjects
Objectives: The aim of this study was to determine the normal inter-day variations of salivary awakening cortisol in healthy adult individuals and to explore its relationship with sleep quality as measured by Sleep cycle alarm clock.
Methods: Sleep quality
Fifteen adult subjects, 9 females and 6 males, (mean age 38.73±5.18 years), with no previously diagnosed sleep disorders, were included in the study. Subjects were asked to download the free version of the app Sleep cycle alarm clock (Northcube AB 8 Göteborg, Sweden) onto their iPhones through the App Store. All subjects were required to use the app for a minimum of 5 nights at home before participating in the study. After they had used the app for a minimum of 5 nights, subjects used the app for three consecutive nights. Sleep quality < 81% was considered as poor sleep quality .
Morning Salivary Awakening Cortisol Assessment
Five millilitres of whole unstimulated saliva was collected into a graduated tube (50 ml, self-standing centrifuge tubes, Ratiolab, Germany).Subjects were asked to collect saliva immediately after waking up during three consecutive days. Saliva aliquots, (1 ml), were stored at −80°C until analysed. Saliva samples were thawed and centrifuged prior to analysis (1000xg, 5 min). Salivary free cortisol levels were determined using a competitive ELISA kit (Demeditec Diagnostics GmbH, Germany).
Results: Intra-individual variability for morning cortisol was 15-42%. Objective poor sleepers (sleep quality < 81%) had significantly lower salivary awakening cortisol than good sleepers.
Conclusions: Our study shows that the poor sleep quality, measured by Sleep cycle alarm clock for iPhones was associated with decreased salivary awakening cortisol.