Napping at home and alertness on the job in rotating shift workers

Conditions surrounding self-selected napping and its association with waking function were examined in a quasi-experimental study at two worksites with workers on 8- and 12-hour rotating shifts. Nap frequency, sleep quantity, quality and timing were determined from daily questionnaires, and performance/alertness during the workshift was assessed with on-site computerized testing. Results indicated that most napping occurred prior to the first night shift of the week. Napping prior to the first shift supplemented an apparently adequate quantity of main sleep, whereas napping during the workweek compensated for a reduced quantity of main sleep. Sleep quality was rated higher on no-nap days than on nap days and higher prior to the first shift than during the workweek. These results generally support a compensatory view of napping. Worksite performance/alertness testing, however, indicated diminished alertness during the shift on nap days compared to no-nap days, which was not consistent with a compensatory view of napping. Decreased alertness on nap days may have been associated with poorer sleep quality or with differences in circadian rhythm adaptation on those days.