0222 Effects of Simulated Regular and Irregular Sleep-Wake Timing on Dark-Light Schedules

Abstract Introduction Irregular sleep-wake patterns have been associated with later circadian phase, lower academic performance, and many adverse health outcomes. It remains unknown whether the irregular sleep-wake patterns themselves or their associated dark-light patterns drive these effects. We designed an inpatient protocol to assess the effect of regular and irregular sleep-wake/dark-light patterns on multiple outcomes. Methods Our 26-day inpatient study included: (i) one 24-hour baseline day (8-hour sleep:16-hour wake; sleep scheduled from 00:00-08:00); (ii) 21 days on a randomized Early Regular (ER), Late Regular (LR), or Irregular (IR) sleep-wake/dark-light schedule; (iii) a 30-hour interval of 90-minute “ultradian days”; and (iv) a final 24-hour recovery day (8-hour sleep:16-hour wake). Each randomized schedule (both sleep-wake and light levels) was generated from 7-day sleep-wake schedules collected during an observational study in college students. Light levels were changed at the beginning of each hour during scheduled wake to 4, 50, 90, 450, or 2,500 photopic lux, based on hourly light bins measured by wrist actigraphy, and set to 0 lux during scheduled sleep. Schedules were selected for regularity as defined by a Sleep Regularity Index above 80 (ER and LR schedules) or below 60 (IR schedule). Regular schedules were classified as Early or Late based on sleep midpoint timing. All schedules (3 ER, 4 LR, 4 IR) were selected to have similar sleep durations within a 7-day interval (average 6.5-9 hours per 24-hours). Each 7-day interval was repeated three times to create each final 21-day schedule. Results Morning light exposure (area under the curve AUC of photopic illuminance between 06:00-12:00) was significantly higher for ER compared to LR (p=0.0002) and IR (p=0.002) but not different between LR and IR (p=0.42). Evening light exposure (AUC of photopic illuminance between 18:00-00:00) was significantly lower on ER compared to LR (p=0.004) but not different between ER and IR (p=0.09) or LR and IR (p=0.18). Conclusion The selected early-timed regular, late-timed regular, and irregular schedules had differences in morning and evening light exposure, independent of sleep duration or regularity. This protocol can be used to investigate the impact of these differences on multiple circadian and neurobehavioral outcomes. Support (if any) NIH-R01HL128538