Circadian Sleep Disorders Network - Advocating for people with misaligned body clocks
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Disclaimer: I am not a medical doctor. These are my personal opinions. You should not use the information on this web page for diagnosing or treating a medical or health condition on your own. All decisions regarding patient care should be made with your healthcare provider.

Vitamin B12 and Circadian Sleep Disorders

by James Fadden

Has vitamin B-12 been proven to help CRDs? The short answer is no, but it's a complicated story.

The interest in B-12 for CRDs came about because of one patient. He was one of the earliest reported cases of N24 and the first one that appeared to be successfully treated [1]. He was the first N24 patient treated at the US National Institute of Health. Basically what happened was, this patient was somewhat hypothyroid. Since low thyroid function can lead to B-12 deficiency he decided, in his own, to take a B-12 supplement and found that shortly after his N24 resolved and it came back if he stopped the B-12 The NIH doctors were not sure how widely applicable that finding was, or if it was a fluke or a placebo effect.

However doctors in Japan were very interested in the B-12 approach to N24 and tried it with several N24 patients with variable success. In one survey 2 out of 10 N24 patients were helped. There was some interest in Japan and the US about how it might work and some work was done on that. For example B-12 might increase the effect of light. However, eventually, double-blind placebo-controlled studies were done and in those B-12 was not significantly better than placebo [2,3]. There was a "trend" toward improvement with B-12 in one study, but a trend that does not reach statistical significance is, well...not significant. A total of 50 patients with DSPS and 6 with N24 were studied. The studies used a form of B-12 called methylcobalamin, which is believed to be more effective than the more common cyanocobalamin (although I think the original NIH patient used cyanocobalamin). But even this allegedly more effective form did not exceed placebo. The Japanese doctors decided B-12 was "therapeutically insufficient" as a single treatment.

Since there are a few cases of N24 that seemed to benefit from B-12 it can't be completely ruled out that some people with CRDs might benefit from taking B-12. So it might be worth trying if nothing else works. But given the failure of B-12 in placebo controlled studies I would not consider it is proven to help CRDs.

In general B-12 is viewed as an energizing substance. Some of this reputation may be undeserved. People with B-12 deficiency are certainly lacking in energy (due to anemia and nerve damage) and so giving them a shot of B-12 will certainly energize them. As a result it became common for doctors to give people B-12 as kind of a tonic to boost their energy. Since B-12 deficiency is not rare that often works. Whether it really does help do that in people who are not B-12 deficient to start with is not clear. It could be a placebo effect. But, deserved or not, it does have a reputation as an energizing substance.

In one study on normal subjects B-12 (as methylcobalamin) did lower melatonin levels and reduce sleep time, consistent with a stimulating effect. Another study showed intravenous B-12 to raise body temperature both day and night in normal volunteers, and also increase slow wave sleep, which usually results from higher body temperature [4,5].

In rats under free-running conditions B-12 increases sleep time and makes the period longer (i.e. makes N24 worse). And in a breed of dogs with narcolepsy B-12 causes cataplexy.

The usual oral dose of B-12 is 1,000mcg (1mg). This is actually far more than the body needs which is more like 2-6 mcg. The reason for the high dose is that a few people do not absorb B-12 well and so the dosage is designed to take that into account. Very few people actually need that high dose, but in most cases taking extra does no harm.


  1. Kamgar-Parsi B, Wehr TA, Gillin JC. Successful treatment of human non-24-hour sleep-wake syndrome. Sleep. 1983;6(3):257-64.
  2. Takahashi K, et al. Double-blind test on the efficacy of methylcobalamin on sleep-wake rhythm disorders. Psychiatry Clin Neurosci. 1999 Apr;53(2):211-3.
  3. Okawa M, et al. Vitamin B12 treatment for delayed sleep phase syndrome: a multi-center double-blind study. Psychiatry Clin Neurosci. 1997 Oct;51(5):275-9.
  4. Itoh H,et al. Sleep facilitating effects of Vitamin B-12, in Meier-Ewert K and Okawa M. Sleep-Wake Disorders. New York, NY: Plenum Press; 1997: 175-182.
  5. Uchiyama M, Mayer G, Okawa M, and Meier-Ewert K, Effects of vitamin B12 on human circadian body temperature rhythm, Neurosci Lett. 1995 Jun 2;192(1):1-4
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