Methylcobalamin is active B12. Methylcobalamin is the only one that passes the blood brain barrier and is needed to make melatonin (from the pineal gland). Sublingual methylcobalamin is acitive B12. It can potentially alter the circadian rhythm.


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The relationship between insufficient sleep and diseases has increased the interest in the role of diet and nutrition in sleep. Several studies that assessed sleep quality and sleep-wake disorders using sleep diaries or questionnaires have reported contradictory associations with vitamin B12 (cobalamin) [1, 2, 3].

Cyanocobalamin is metabolized to methylcobalamin upon absorption from the intestinal tract. Of the two forms of vitamin B12, only methylcobalamin passes the blood brain barrier and is important for the synthesis of melatonin, a major hormone that regulates sleep [18, 19, 20]. Interestingly, animal studies which involved direct injection of both forms of vitamin B12 into the third ventricle of the brain provided some indication that cyanocobalamin has no direct effect on sleep [21]. For future studies of cyanocobalamin supplementation on sleep, consideration should be given to including an analysis of changes in melatonin concentrations. Future studies should also include a control group, screen for physical health, control for diet, alcohol use and exercise, and exclude persons with mental illnesses/depression and stress.