Figure 1. Study schedule.

Dark bars represent the scheduled sleep episodes. Subjects completed a 39-day protocol with a baseline ‘sleep replete’ condition with 3 weeks of 10 h/day of time in bed (TIB) at home, then 6 days with ≥10 h TIB per day. Sleep opportunities were then spread across the circadian cycle on a 28-h “forced desynchrony” (FD) protocol, with 6.5 h TIB (equivalent to 5.6 h per 24h) and 21.5 h of monitored wakefulness for 3 weeks. A subsequent period of 10 days of circadian re-entrainment with sleep recovery (10 h TIB/24 h) with the sleep period adjusted to the same circadian phase as the baseline sleep condition by modification of the duration of the wake period after the last FD day. Standardized breakfast meal responses (B); daily fasted blood samples for assessment of glucose, insulin, cortisol (F); core body temperature minimum (white X). Time from midpoint of sleep to start of breakfast (grey horizontal arrow) was maintained by choosing a day in the last week of sleep restriction plus circadian disruption such that the standardized meal occurred during this exposure at the same circadian phase as baseline within 4 h (0.7 ± 1.8 h), resulting in an average exposure duration of 19.2 ± 2.8 24-h days (range 15-22 days).