title: Light-induced melatonin suppression at night after exposure to different wavelength composition of morning light.
abstract: Bright nocturnal light has been shown to suppress melatonin secretion. However, bright light exposure during the day might reduce light-induced melatonin suppression at night. The human circadian system is sensitive to short wavelength light. This study evaluated the preventive effect of different wavelengths of daytime light on light-induced melatonin suppression at night. Twelve male subjects were exposed to various light conditions (dim, white, and bluish white light) between the hours of 09:00 and 10:30 (daytime light conditions). They were then exposed to light (300lx) again between 01:00 and 02:30 (night-time light exposure). Subjects provided saliva samples before (00:55) and after night-time light exposure (02:30). A two-tailed paired t-test yielded significant decrements in melatonin concentrations after night-time light exposure under daytime dim and white light conditions. No significant differences were found in melatonin concentrations between pre- and post-night-time light exposure with bluish-white light. Present findings suggest that daytime blue light exposure has an acute preventive impact on light-induced melatonin suppression in individuals with a general life rhythm (sleep/wake schedule). These findings may be useful for implementing artificial light environments for humans in, for example, hospitals and underground shopping malls to reduce health risks.
authors.affiliation: Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan. Electronic address: kozaki@design.kyushu-u.ac.jp.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kozaki
authors.affiliation: Graduate School of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan.
authors.forename: Ayaka
authors.initials: A
authors.lastname: Kubokawa
authors.affiliation: Graduate School of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan.
authors.forename: Ryunosuke
authors.initials: R
authors.lastname: Taketomi
authors.affiliation: Graduate School of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Hatae
mesh_terms: D002940:Circadian Rhythm; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D012463:Saliva / Q000378:metabolism*; D055815:Young Adult
chemical_list: D008550:Melatonin
keywords: Daytime; Light; Melatonin; Night-time; Wavelength