Figure 1.

Study Protocol and Phase of SCN-Driven Hormone Rhythms

(A) In order to maximize circadian entrainment prior to beginning the study protocol, participants maintained a self-selected pre-laboratory light-dark and sleep-wake pattern based on their habitual routine for 10 days. During the last week of the pre-laboratory period they ate breakfast (B) 30 min after wake, lunch (L) 5.5 hr after wake, and dinner (D) 10.5 hr after wake. Participants then entered the laboratory on day 0. During days 0–3, participants remained on their self-selected sleep-wake cycle. They slept in individual bedrooms in darkness (0 lux; black bars) and were awake in bright room light (∼500 lux in direction of gaze) during the day. Waking time was spent in communal areas (white bars) and in individual rooms (dotted bars). Isocaloric meals (B, L, D) were given 0.5, 5.5, and 10.5 hr after waking up, matching the week of pre-laboratory meal timing. On day 4, participants began a 37-hr constant routine in individual rooms (<8 lux; gray bars). Participants had a standard night’s sleep on day 5, before 6 more days of the sleep-wake and light-dark cycles (days 6–11). Conditions were equal to days 1–3 except for a 5-hr delay in all meal times. A second constant routine then commenced on day 12. Immediately before and after each constant routine, participants were kept in a constant routine-like environment but allowed to move within their rooms (hatched bars).

(B and C) Concentration of melatonin (B) and cortisol (C) in hourly plasma samples collected in constant routine conditions. Black circles with solid lines represent data following early meals (0.5, 5.5, and 10.5 hr after waking up). White squares with dashed lines represent data following a 5-hr delay in each meal. Two-way repeated-measures ANOVA revealed a significant effect of time (melatonin: F_{(31, 279)} = 19.00, p < 0.001; cortisol: F_{(31, 279)} = 20.31, p < 0.001), but no significant effect of meals (melatonin: F_{(1, 9)} = 2.97, p = 0.119; cortisol: F_{(1, 9)} = 2.27, p = 0.166) or meal × time interaction (melatonin: F_{(31, 279)} = 0.13, p = 0.124; cortisol: F_(31, 279) = 1.39, p = 0.090). Data are mean ± SEM, n = 10. Statistical significance is defined as p < 0.01 (following Bonferroni correction for analysis of a total of five rhythmic plasma markers).

See also Figures S1 and S2.