Some early research has explored vitamin B12 supplementation in relation to sleep regulation and circadian rhythm disturbances, though the evidence is limited to small observational and case-based reports.
A brief report published in the Japanese Journal of Psychiatry and Neurology (1991; 45(1): 165–166) described five patients, ages 14 to 60, with a range of sleep-related conditions, including insomnia, delayed sleep-phase syndrome, non–24-hour sleep–wake rhythm disorder, and depression. Participants received vitamin B12 at a dose of 4.5 mg per day, divided into three doses.
During the treatment period, serum vitamin B12 levels increased two- to fourfold. The authors reported improvements in sleep-related symptoms in these cases, though no standardized sleep metrics or control group were used.
Additional observations were presented at the World Congress of Biological Psychiatry in 1991. In this report, eight individuals aged 12 to 63 with sleep–wake rhythm disorders were evaluated. Two participants had non–24-hour sleep–wake rhythm disorder, four had delayed sleep-phase syndrome, and two had insomnia. Vitamin B12 was administered at a dose of 1.5 mg three times daily.
Improvements were reported in individuals with sleep–wake rhythm disturbances, in those with insomnia, and in one participant with delayed sleep-phase syndrome. In one case where vitamin B12 alone did not produce improvement during the first month, adjunctive phototherapy (2,500 lux for two hours each morning) was introduced and was associated with improvement in sleep symptoms.
Notably, the authors observed that participants who responded to vitamin B12 supplementation were not necessarily deficient at baseline. They also reported that sleep–wake rhythm disturbances often recurred days to weeks after discontinuation of vitamin B12 therapy.
These reports represent early, small-scale investigations into a possible relationship between vitamin B12 and circadian rhythm regulation. They were not designed to establish efficacy, determine optimal dosing, or assess long-term outcomes, but they helped generate interest in the potential role of B12 in sleep–wake biology.
