CHANGES IN CORTISOL SECRETION DURING SHIFTWORK - IMPLICATIONS FOR TOLERANCE TO SHIFTWORK

The present study was conducted to determine the size of changes and t he time point of those changes in biological rhythms during night-shif t and whether they are associated with tolerance to shiftwork. The adr enal hormone cortisol has frequently been investigated in the field of shiftwork since it follows a pronounced circadian variation and has b een demonstrated to be affected by night-work. However, studies are re stricted with respect to sample size, number of measurements or durati on of sampling periods. Therefore, a sample of 24 night-shift workers was investigated in a cardiac emergency unit for seven nights. Saliva samples were collected frequently for determination of cortisol. A tot al of 28 cortisol measurements in each subject were made in order to d ecide whether the circadian rhythm changed, and if so at which time po int. A clear reversal of circadian function could be observed for the total group (mean cortisol concentrations) after the fifth night. Howe ver, inspection of individual patterns revealed that six out of 24 sub jects did not change in circadian function. These subjects exhibited l ower durations of and less consistency in recovery sleep across the fo llowing days after night-work. With respect to personality dimensions a pattern associated with neuroticism can be observed in subjects with out appropriate changes in cortisol rhythm. However, owing to the smal l sample size of non-adapters these results are preliminary and should be replicated with larger samples. The overall relationship between n euroticism and low adaptability has been discussed.