Cortisol measurements in the workplace as stress indicators

Introduction
The cortisol hormone, a biomarker of stress, may be associated with physical and mental health outcomes. This study aims at evaluating various methods of cortisol measurements and their daily variations on working days and resting days

Methods
In an ongoing research project, saliva samples were collected on 132 workers in 13 workplaces in Canada. Consenting workers provided 5 saliva samples a day (awakening, 30 minutes after awakening, 2 pm, 4 pm, bedtime) repeated 3 times (Saturday, Tuesday, Thursday) over a week, to provide measures at work and during resting times and settings. Salivary cortisol concentrations were determined by radioimmunoassay. All samples were assayed in duplicates. 28% of workers were females, mean age was 41.9 (SD=9.49; range 20-63) and average work-hours per week were 40.05 (SD=6.52, ranged 8-68). Multilevel regression models were estimated with saliva samples at level-1, days at level-2 and workers at level-3. These results were compared with three conventional methods, the MESOR, the diurnal curve and the cortisol awakening response (CAR)

Results
Controlling for gender and age, results show significant cortisol concentration variations at samples, days and workers levels. Cortisol increases from awakening to 30 minutes after awakening and then declines sharply. Cortisol increases linearly from non-working day to work days and work hours interact with days. Gender and age had neither main effects nor interaction effects. As for the conventional methods, these latter methods provide comparable results for the overall between day differences.

Discussion
Overall, these preliminary results suggest that work hours act as a stressor associated with variation in cortisol concentration. Cortisol increases in relation to work time and the daily duration of work. Multilevel regression analyses provide as precise information as the conventional methods and cortisol measurements provide useful information on the weekly duration of work and the following recuperation during resting days.