The normalization of the cortisol awakening response and of the cortisol shift profile across consecutive night shifts—An experimental study

Jun 24, 2010Psychoneuroendocrinology

How the body's morning stress hormone response returns to normal during back-to-back night shifts

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Abstract

The cortisol awakening response (CAR) increased gradually across four consecutive night shifts, reaching baseline levels after 3 days for men and 4 days for women.

The study involved 18 students, evenly split by gender, who worked alternating morning and night shifts.
A 2-hour bright light pulse helped advance the circadian system by 5 hours.
Cortisol levels during night shifts showed a gradual decline, correlating with increases in the CAR.
The CAR may be influenced by the anticipation of upcoming work demands, beyond just circadian adjustments.

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This study tested the hypothesis that the cortisol awakening response (CAR) and the cortisol shift profile normalize with successive night shifts due to the shift of the circadian system. 18 students (9 women, 9 men, 19-29 years), worked first four consecutive morning- and then four consecutive night shifts. Each work shift was preceded by an 8-h sleep opportunity meaning that the sleep-activity cycle was advanced by 8 h. The advance of the circadian system was promoted by a 2-h bright light pulse at the end of each night shift and quantified by 24-h phase assessment procedures (PA) before and after the four day shifts and again after the four night shifts. Saliva samples were taken 0, 15, 30, 45, and 60 min post-awakening, hourly during each work shift and each PA. During the night shift sequence, the CAR, indicated by the area under curve with respect to increase (AUC(I)), increased gradually across the 4-day sleep periods. Baseline levels were reached after 3 days in men and 4 days in women. The increase of the CAR was associated with a gradually increasing decline of cortisol levels during the night shifts. This adjustment was--at least not only--related to the advance of the circadian system which was 5 h. A contributor to the increase of the CAR might be the anticipation of the upcoming demands of the following work shifts.

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The normalization of the cortisol awakening response and of the cortisol shift profile across consecutive night shifts—An experimental study

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