title: Vitamin B12 enhances the phase-response of circadian melatonin rhythm to a single bright light exposure in humans.
abstract: Eight young males were subjected to a single blind cross-over test to see the effects of vitamin B12 (methylcobalamin; VB12) on the phase-response of the circadian melatonin rhythm to a single bright light exposure. VB12 (0.5 mg/day) or vehicle was injected intravenously at 1230 h for 11 days, which was followed by oral administration (2 mg x 3/day) for 7 days. A serial blood sampling was performed under dim light condition (less than 200 lx) and plasma melatonin rhythm was determined before and after a single bright light exposure (2500 lx for 3 h) at 0700 h. The melatonin rhythm before the light exposure showed a smaller amplitude in the VB12 trial than in the placebo. The light exposure phase-advanced the melatonin rhythm significantly in the VB12 trail, but not in the placebo. These findings indicate that VB12 enhances the light-induced phase-shift in the human circadian rhythm.
authors.affiliation: Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Hashimoto
authors.forename: M
authors.initials: M
authors.lastname: Kohsaka
authors.forename: N
authors.initials: N
authors.lastname: Morita
authors.forename: N
authors.initials: N
authors.lastname: Fukuda
authors.forename: S
authors.initials: S
authors.lastname: Honma
authors.forename: K
authors.initials: K
authors.lastname: Honma
mesh_terms: D000328:Adult; D002940:Circadian Rhythm / Q000187:drug effects*; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000502:physiology*; D010919:Placebos; D014805:Vitamin B 12 / Q000494:pharmacology*
chemical_list: D010919:Placebos; D008550:Melatonin; D014805:Vitamin B 12