What role does B12 play in sleep?

Vitamin B12 (cobalamin) is essential for methylation and myelin synthesis, processes that influence neurotransmitter production (serotonin, melatonin) and nerve function—both relevant to sleep regulation. B12 deficiency can cause fatigue, neuropathy, and cognitive disturbances that impair sleep quality. However, direct evidence that B12 supplementation improves sleep in individuals with adequate levels is weak. Some studies suggest B12 may help regulate circadian rhythms via melatonin synthesis, but findings are inconsistent. Overall, B12's role in sleep is indirect and context-dependent. If deficiency is suspected, a blood test is recommended before supplementing. The evidence is primarily mechanistic rather than from robust clinical trials.