Fig 1.
Schematic representation of the experimental protocol for morning (A) and evening (B) light exposure. Participants arrived in the early evening of Day 1 (not shown) and began dim light < 20 lux (light grey shading) on Day 2 during 16 hours of wake and < 3 lux (dark grey shading) during 8 hours of sleep. Fixed isocaloric meals were given 1, 5, and 11 hours after wake. On both Days 2 and 3, questionnaires (VASH and KSS) were collected hourly during wake and blood was drawn (black circles) at 30-minute intervals 0.5–4.5 hours after wake for morning light exposure participants (A) and 10.5–14.5 hours after wake for evening light exposure participants (B). Participants were exposed to 3 hours of blue-enriched light (hashed shading on Day 3) starting 0.5 hours after wake for morning light exposure participants (A) and starting 10.5 hours after wake for evening light exposure participants (B) compared to dim light (Day 2). Participants were discharged on Day 4 (not shown). Abbreviations: VASH–visual analogue scale for hunger, KSS–Karolinska Sleepiness Scale.
Table 1.
Participant demographics and characteristics shown as M±SD or No. (%).
Fig 2.
Hunger in dim versus blue-enriched morning and evening light.
Subjective hunger composite scores (A-B) and component scores (C-J) during dim light (dotted line) compared to blue-enriched light (solid line) for morning (left panels; n = 9) and evening (right panels; n = 10) participants. Grey shading indicates specified light exposure condition; M denotes meal given 1 or 11 hours after wake for morning and evening participants, respectively. Results are plotted as mean ± standard error.
Table 2.
Change from baseline (prior to start of light exposure) in leptin and ghrelin measures, between conditions (dim versus blue-enriched light) within each group and between groups (morning versus evening).
Fig 3.
Glucose, insulin, and HOMA-IR in dim versus blue-enriched morning and evening light.
Glucose levels (A-B), insulin levels (C-D), and homeostatic model assessment of insulin resistance (E-F) during dim light (dotted line on line plots and grey bar on bar graph) compared to blue-enriched light (solid line on line plots and black bar on bar graph) for morning (n = 9; n = 8 for insulin and HOMA-IR) and evening (n = 10) participants. Grey shading on line plots indicates specified light exposure condition; M on line plots denote meal given 1 or 11 hours after wake for morning and evening participants, respectively. Results are plotted as mean ± standard error. *p<0.05, **p<0.01.
Table 3.
Glucose, insulin, HOMA-IR, and cortisol between conditions (dim versus blue-enriched light) within each group and between groups (morning versus evening).
Fig 4.
Sleepiness and cortisol in dim versus blue-enriched morning and evening light.
Subjective sleepiness (A-B) and cortisol levels (C-D) during dim light (dotted line) compared to blue-enriched light (solid line) for participants in the morning (n = 8 for sleepiness and n = 9 for cortisol) and evening (n = 9 for sleepiness and n = 10 for cortisol) groups. Grey shading indicates specified light exposure condition; M denotes meal given 1 or 11 hours after wake for morning and evening participants, respectively. Results are plotted as mean ± standard error.