Introduction Night work is associated with shorter sleep and greater chronic disease risk compared with day work, and older shiftworkers report even greater difficulty sleeping compared with younger workers. We tested a sleep and circadian rhythm intervention to examine whether it improved sleep duration and cortisol, a marker of physiological stress.

Methods 26 healthy adults (57.6±3.9 y) who were not shiftworkers participated. Four laboratory Day shifts were followed by four Night shifts. Participants slept at home and maintained ~8 hour sleep schedules for a week before study and on Day shifts. After the first Night shift, participants were randomised into groups with different sleep instructions: control ad lib sleep (n=9); 8 hour evening sleep plus a light intervention (n=9); 8 hour evening sleep (n=5). The evening sleep groups were instructed to get into bed between 1–2 pm and remain in bed attempting to sleep for 8 hour. Sleep was monitored by actigraphy. At the start of the 4th Day shift and end of the 4th Night shift, a blood sample was taken for cortisol assay.

Results The sleep duration and cortisol level of the groups were not different at baseline. The 8 hour evening sleep groups showed similar sleep durations following night and day shifts, while the control group had shorter sleep (p<0.001). At the end of the 4th Night shift, the 8 hour evening sleep groups had significantly lower cortisol levels compared with the control group (p<0.02).

Discussion Our preliminary data indicate an 8 hour scheduled evening sleep episode after night shifts results in longer sleep in older shiftworkers, and this was associated with lower cortisol levels. While this remains to be tested in actual night workers, it suggests that the sleep intervention may have implications for improved health outcomes in older shiftworkers.

Grants R01AG044416, UL1TR001102, T32HL007901 from the NIH; Dancook University (to JHK).