Exposure to bright light during evening class hours increases sleep quality and mood among working college students

Abstract

The sleep–wake cycle (SWC) is a biological rhythm influenced by internal and external informations, as environmental and psychological factors and work/study times. Recent studies show that bright light over specific hours of the day might act as SWC synchronizer, reducing working college students’ sleepiness. The aim of this study was to evaluate the effects of exposure to bright light on sleep quality, mood and easiness of sleep and to wake up during evening hours among working college students. The subjects were healthy 21–24 years old young men attending night classes and working during the day. Over three weeks the subjects filled activities protocols, which include four analog visual scales (VAS: sleep quality, mood and easiness to sleep and wake up), wore actigraphs and registered their sleepiness levels three times each night (19:00 h, 20:30 h and 22:00 h) using Karolinska Sleepiness Scale (KSS). At second and third weeks the subjects, divided in two groups, were exposed to bright light (8.000 lux) for 20 min at 19:00 h or 21:00 h in a crossover design. Salivary melatonin samples were collected prior and after exposure. Pearson Correlation tests were performed. Melatonin onset points (20:00 h and 21:30 h) were defined at 4 pg/mL salivary concentrations. After variables relativization, statistical differences were found when comparing the week prior intervention and 19 h intervention week (prior and intervention weeks means, respectively): 7.1/ 7.3 pts for easiness of sleep (r = 0,69; p < 0.01); 3.9/4.5 pts for easiness to wake up (r = 0,66; p < 0.01); 5.7/6.7 pts for sleep quality (r = 0,74; p < 0.01) and 6.1/5.4 pts for mood (r = 0,66; p < 0.01). No differences were found for VAS values over the 21 h exposure week. Despite the sample size and literary evidences on different time and duration of intervention (one hour at least, in the middle of the day), the results of this study point out to a better perception of sleep quality, easiness of sleep and to wake up, and worse perception of mood with reduced exposure and in the evening hours. Support: CNPq (501766/2007-3; 500782/2008-3; 472153/2006-4; 307919/2006-4); CAPES, FAPESP (07/04648-4; 06/59053-2), FAPERJ (E-26/102.965/2012), PIBIC-CNPq.