EFFECTS OF TIMED BRIGHT-LIGHT EXPOSURE ON SHIFT-WORK ADAPTATION IN MIDDLE-AGED SUBJECTS

Shift workers suffer from a constellation of symptoms that can severel y compromise their ability to perform optimally on-shift. The largest single factor contributing to shift-worker problems is sleep disturban ce, and there is little question that the primary cause of such sleep disturbance is circadian disruption. Recently, a number of studies hav e demonstrated that timed exposure to bright light can help facilitate adaptation to simulated shift-work schedules, at least in younger sub jects. The aim of the current study was to assess the effects of brigh t-light interventions in middle-aged individuals undergoing a simulate d shift-work regimen. Results indicate that although light was effecti ve in resetting the circadian clocks of these subjects by more than 6 hours, there was little effect on measures of on-duty alertness and pe rformance or on off-duty sleep. These findings suggest that middle-age d subjects may be less phase-tolerant than young subjects, and they ra ise questions concerning the utility of bright-light interventions in some shift-work populations.