Shiftworkers report worse sleep than day workers, even in retirement

The aim of this study was to explore how the level of shiftwork exposure during an individual's working life might be related to subjectively reported sleep quality and timing during retirement. Telephone interviews regarding past employment and sleep timing and quality (among other variables) were conducted using a pseudo-random age-targeted sampling process. Subjective sleep quality was assessed using a telephone version of the Pittsburgh Sleep Quality Index. Timing of reported habitual bedtimes and rise-times were assessed using the Sleep Timing Questionnaire. Questions measuring morningness and subjective health were also given. Retired seniors (aged >65 years, n = 1113) were studied. Analysis was by analysis of variance, with shiftwork exposure in three bins [0 (n = 387), 1-15 (n = 371) and >15 years (n = 355)], gender (n = 634 male, 479 female) and former occupation [in two broad categories, 'managerial' (n = 437) versus 'other' (n = 676)] as factors. In retired shiftworkers, relative to retired day workers, past exposure to shiftwork was associated with higher (worse) PSQI scores by 1.0 units (1-15 years) and 0.6 units (>15 years) (main effect P = 0.005). There were also main effects of gender and former occupation (males and managerials reporting better sleep), but neither variable interacted with shiftwork exposure. The timing of current mean habitual bedtimes and rise-times (and also the variance around them) were very similar for the three shiftwork exposure groups. The shiftwork exposure effect did not appear to be mediated by either morningness or current health. Prior exposure to shiftwork would appear to be related to currently reported sleep problems during retirement.