Vitamin B12 enhances the phase-response of circadian melatonin rhythm to a single bright light exposure in humans

Neurosci Lett. 1996 Dec 13;220(2):129-32. doi: 10.1016/s0304-3940(96)13247-x.


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.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Circadian Rhythm / drug effects*
  • Humans
  • Light*
  • Male
  • Melatonin / physiology*
  • Placebos
  • Vitamin B 12 / pharmacology*


  • Placebos
  • Melatonin
  • Vitamin B 12