Stress, strain, and other intervening variables in shiftwork were studied. Measurement of oral temperature of 133 experienced shift workers (SW) indicated that the circadian rhythm of temperature remained unchanged during the first night shift. No inversions were observed until the seventh night shift. One group of researchers found only flattening of circadian rhythm, while another group found a tendency toward increase. Transference of minimum body temperature rhythm was not evident on the 12th night shift day in one study nor on the 21st consecutive night shift day in another study. Reentrainment was achieved more quickly but only partially with experimental shift work as compared to field conditions. In comparing nurses who worked part time or 16 full time night shifts, it was observed that full timers showed long term adjustment. Sleep, appetite, and gastrointestinal disturbances were reported for SW and continuous night workers in many industries by several researchers. Clear differentiation between various groups could not be made because of wide overlap in findings. No increases in mortality of night SW were observed, but workers who gave up shiftwork prematurely had a higher mortality ratio. Gastric ulcers were found among 10 to 30 percent of SW who had given up shiftwork, 2.5 to 15 percent of SW doing night shift, and 5 percent of SW not working night shift. Shift work showed no effect on cardiovascular diseases, neurological disturbances, and psychiatric illness, however, it caused social disturbances. The authors state that single night shifts are better than consecutive night shifts, that at least 24 hours of free time should be allowed after each night shift, that length of shift should be related to type of work, that shift system cycles should not be too long, and that as many free weekends as possible should be arranged.
The Twenty-Four Hour Workday: Proceedings of a Symposium on Variations in Work-Sleep Schedules, Division of Biomedical and Behavioral Science, NIOSH, U.S. Department of Health and Human Services, Cincinnati, Ohio, DHHS (NIOSH) Publication No. 81-127