Circadian biological characteristics after shifting sleep and meal times

In order to examine differences among individuals and among variables related to the rate of shift of the circadian system, nine male students were studied for 72 h under controlled physical environmental conditions. During this 3-day test, they were subjected to a 12-hour shift in the times of sleep and meals. Differences in the rate of shift from day 1 to day 3 were observed for blood pressure and urinary cortisol, norepinephrine and dopamine, but not for other urinary variables or for heart rate, temperature and body weight. Inter-individual differences in the rate and/or direction of adjustment were seen primarily for blood pressure and heart rate. The experimental design used in this study may detect differences in the suitability of a subject for shift-work.