Workers Need at Least 11 Hours Off Between Shifts

How much time off between shifts do workers need to get adequate sleep?

According to London-based CIRCADIAN, a provider fatigue risk management systems, shift schedule optimization services, and shift worker training, the answer is somewhere between 11 and 16 hours.

Citing a 1994 study that appeared in the journal Ergonomics, the firm noted there is a very high correlation with sleep duration and the length of time off between consecutive shifts. The 1994 study (by N. Kurumatani, et al.) concluded that individuals need at least 16 hours of time off to have a sleep duration of seven or eight hours.

More recent studies have shown that rest periods of 10 hours or less between consecutive shifts result in short sleep episodes, sometimes lasting only three to five hours. CIRCADIAN notes that one 1997 study published in the Chronobiology International concludes that the time off between the end of one shift and the beginning of the next one should thus be at least 11 hours.

In a separate report examining the limits of consecutive workdays and overtime, CIRCADIAN says it generally recommends limiting eight-hour shifts to a maximum of seven in a row, and 12-hour shifts to four or five in a row. The firm notes that, given differences in work environment, physical and mental work-related stress, and individual circumstances, it is difficult to recommend specific limits, and it is equally important to consider the number of hours worked per week. Studies show "long hours increase stress levels, both by increasing the demands of maintaining performance while facing increased fatigue levels, and by increasing the time a worker is exposed to other sources of workplace stress," CIRCADIAN says.

"There is growing evidence that excessive long hours directly correlate with health problems, as a result of the increased stress levels and chronic sleep deprivation and fatigue," the company adds. These health problems include cardiovascular and musculoskeletal issues, gastrointestinal disorders, and certain mental problems. CIRCADIAN cites a 1992 study in the Journal of Human Ergology (by T. Uehata) that analyzed the lifestyle of more than 200 people who had suffered a heart attack; the results showed 65 percent in the group regularly worked more than 60 hours per week, with some working more than 50 hours of overtime a month as well as half of their contracted holidays. CIRCADIAN notes that the annual overtime hours for shiftworkers has been steadily increasing over the past decade as businesses strive to do "more with less" and concludes that "[w]hen considering the amount of hours worked, it is thus important to take into account not only the regular hours, but also the overtime, mandatory or voluntary."

For more information on shiftwork, scheduling, and sleep patterns, visit www.circadian.com.

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