title: Effectiveness of a red-visor cap for preventing light-induced melatonin suppression during simulated night work.
abstract: Bright light at night improves the alertness of night workers. Melatonin suppression induced by light at night is, however, reported to be a possible risk factor for breast cancer. Short-wavelength light has a strong impact on melatonin suppression. A red-visor cap can cut the short-wavelength light from the upper visual field selectively with no adverse effects on visibility. The purpose of this study was to investigate the effects of a red-visor cap on light-induced melatonin suppression, performance, and sleepiness at night. Eleven healthy young male adults (mean age: 21.2±0.9 yr) volunteered to participate in this study. On the first day, the subjects spent time in dim light (<15 lx) from 20:00 to 03:00 to measure baseline data of nocturnal salivary melatonin concentration. On the second day, the subjects were exposed to light for four hours from 23:00 to 03:00 with a nonvisor cap (500 lx), red-visor cap (approx. 160 lx) and blue-visor cap (approx. 160 lx). Subjective sleepiness and performance of a psychomotor vigilance task (PVT) were also measured on the second day. Compared to salivary melatonin concentration under dim light, the decrease in melatonin concentration was significant in a nonvisor cap condition but was not significant in a red-visor cap condition. The percentages of melatonin suppression in the nonvisor cap and red-visor cap conditions at 4 hours after exposure to light were 52.6±22.4% and 7.7±3.3%, respectively. The red-visor cap had no adverse effect on performance of the PVT, brightness and visual comfort, though it tended to increase subjective sleepiness. These results suggest that a red-visor cap is effective in preventing melatonin suppression with no adverse effects on vigilance performance, brightness and visibility.
authors.affiliation: Department of Human Science, Faculty of Design, Kyushu University, Japan. higu-s@design.kyushu-u.ac.jp
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Higuchi
authors.forename: Tomomi
authors.initials: T
authors.lastname: Fukuda
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kozaki
authors.forename: Masaya
authors.initials: M
authors.lastname: Takahashi
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Miura
mesh_terms: D000704:Analysis of Variance; D021081:Chronobiology Disorders / Q000517:prevention & control*; D003020:Clothing; D018592:Cross-Over Studies; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism* / Q000528:radiation effects; D012463:Saliva / Q000737:chemistry; D013057:Spectrum Analysis; D013647:Task Performance and Analysis; D014851:Wakefulness / Q000502:physiology; D014940:Work Schedule Tolerance / Q000502:physiology*; D055815:Young Adult
chemical_list: D008550:Melatonin