Vitamin B12

Authored by Laya Rajan and Robert Chen • 
July 10, 2016
 • 4 min read

Take Home Points

  • Vitamin B12 is a naturally occurring water-soluble compound, essential for generating new red blood cells, maintaining neurologic function, and DNA synthesis.

  • A B12 deficiency can cause neurological symptoms such as memory loss, irritability, and a reversible form of dementia.

  • Cyanocobalamin is the primary form used in most nutritional supplements, which is processed to an active form in the body.

  • Vitamin B12 has been shown to improve working memory with consistent use.

Name: Vitamin B12, also known as cyanocobalamin, cobalamin, methylcobalamin, 5-deoxyadenosylcobalamin, adenosylcobalamin, cobamamide, dibencozide, hydroxocobalamin

Source: Naturally found in meat, fish, eggs, and dairy products.

Structure: Vitamin B12 is found in the cyanocobalamin form, which gets converted to methylcobalamin and hydroxocobalamin, which are the active forms that can have effects in the body.

The structure of vitamin B12. The structure of vitamin B12.

Effects on the Brain

Vitamin B12 has been shown to have beneficial effects on cognitive function as well as general health of neurons. The functional forms of B12, methylcobalamin and hydroxocobalamin, have been shown to improve memory, as well as neurogenesis, maintenance of neuronal structure and axon growth.


No significant findings to date.


In healthy adults 50-75, an antioxidant blend including 720 mcg methylcobalamin resulted in improved memory after 4 months of daily use.1

Supplementation with methylcobalamin contributes to improvements in working memory as measured by the Names-Learning paired association test.

Supplementation with methylcobalamin contributes to improvements in working memory as measured by the Names-Learning paired association test (NLT).

Supplementation with methylcobalamin contributes to improvements in working memory as measured by the Word Recall Task Supplementation with methylcobalamin contributes to improvements in working memory as measured by the word-recall test (WRT).

Mood and Emotion

B12 deficiency has been reliably correlated with melancholic depression symptoms.2. After adjusting for other factors such as chronic disease conditions, scientist concluded that B12 probably plays a causative role. A study has also shown that levels of B12 in the blood were also predictive of depression in the study population of over 3000 people.


No significant findings to date.


No significant findings to date.


No significant findings to date.

Side Effects

There are no major side effects if taken in safe quantities.

Mild side effects:

  • Diarrhea
  • Swelling

Rare but serious side effects:

  • Shortness of breath
  • Headache
  • Exhaustion
  • Flushed skin
  • Irregular heartbeat

##Safety Vitamin B12, and specifically methylcobalamin and cyanocobalamin, are approved as a dietary supplement component (generally recognized as safe)

##Mechanism of Action Vitamin B12 in most supplements is in the cyanocobalamin form. This is broken down into an active form, and then processed further. Most importantly, B12 is absorbed in the gut by binding to a protein called intrinsic factor. See below for a detailed diagram of this process.

Cobalamin absorption and conversion in the bloodstream and cells. From: Obeid, R., Fedosov, S. N., & Nexo, E. (2015). Cobalamin coenzyme forms are not likely to be superior to cyano‐and hydroxyl‐cobalamin in prevention or treatment of cobalamin deficiency. Molecular nutrition & food research.

##Effects on Disease States

Alzheimer's Disease

In a study involving 10 patients with Alzheimer's disease, methylcobalamin was found to improve various intellectual functions such as memory, emotional control, and interactions with other people.3

Increasing amounts of evidence suggest that methylcobalamin can be useful for lowering homocysteine, a biomarker for inflammation that is elevated in cases of Alzheimer's disease.4

Studies have shown that dietary supplementation of B vitamins including vitamin B12 are associated with lower levels of inflammatory biomarkers for vascular dementia such as thromboxane, homocysteine, and isoprostane (See Figure 1).5


Supplementation with vitamin B6 and B12 is associated with decreases in levels of inflammatory biomarkers for vascular dementia such as homocysteine, thromboxane and isoprostane.

Vascular Disease

A study of 113 50-75 year olds without dementia showed a significant decrease in serum homocysteine levels over 4 months as a result of 720 micrograms of B12 given daily. A high level of homocysteine increases risk for injury to blood vessels, which can lead to cardiovascular diseases. This suggests that B12 may have a vascular protective effect.1

Peripheral Neuropathy

Peripheral neuropathy is nerve damage that occurs outside of the brain. It frequently occurs in hands and feet, and can cause pain, tingling, weakness, and numbness. A recent meta-analysis of 1221 peripheral neuropathy patients found that combining methylcobalamin and lipoic acid resulted in drastic improvements in nerve function. This suggests that there may be a synergistic effect of lipoic acid along with methylcobalamin, and deserves further study.6. Another study found that methylcobalamin combined with prostaglandin E1 was an effective treatment for peripheral neuropathy caused by diabetes.7

Interestingly, a study in rats found that methylcobalamin facilitates regrowth of nerves .8Although studies in animal models do not always translate to humans, this is motivation to continue exploring whether B12 can help repair nerve damage in humans.

Herpetic Neuralgia

A study involving 98 patients with herpetic neuralgia (pain related to infection with herpes zoster virus, commonly known as shingles), showed that taking injections of methylcobalamin reduced pain significantly.9

How to take

Take 1 mg in capsule form is an appropriate daily dose for those who are at risk for deficiency. For an acute effect on cognitive performance The Mayo Clinic recommends taking 50-100mcg.

  1. Summers, W. K., Martin, R. L., Cunningham, M., DeBoynton, V. L., & Marsh, G. M. (2010). Complex antioxidant blend improves memory in community-dwelling seniors. Journal of Alzheimer's Disease, 19(2), 429.

  2. Timelier, H., van Tuijl, H.R., Hofman, A., Meijer, J., Kiliaan, A.J., Breteler, M.M. Vitamin B12, folate, and homocysteine in depression: the Rotterdam Study. Am J Psychiatry. 2002 Dec;159(12):2099-101.

  3. Ikeda, T., Yamamoto, K., Takahashi, K., Kaku, Y., Uchiyama, M., Sugiyama, K., & Yamada, M. (1991). Treatment of Alzheimer-type dementia with intravenous mecobalamin. Clinical therapeutics, 14(3), 426-437.

  4. McCaddon, A., & Hudson, P. R. (2010). L-methylfolate, methylcobalamin, and N-acetylcysteine in the treatment of Alzheimer's disease-related cognitive decline. CNS spectrums, 15(S1), 2-5.

  5. Clarke, R., Harrison, G., & Richards, S. (2003). Effect of vitamins and aspirin on markers of platelet activation, oxidative stress and homocysteine in people at high risk of dementia. Journal of internal medicine, 254(1), 67-75.

  6. Jiang, D. Q., Li, M. X., Wang, Y., & Wang, Y. (2015). Effects of prostaglandin E1 plus methylcobalamin alone and in combination with lipoic acid on nerve conduction velocity in patients with diabetic peripheral neuropathy: A meta-analysis. Neuroscience letters, 594, 23-29.

  7. Deng, H., Yin, J., Zhang, J., Xu, Q., Liu, X., Liu, L., ... & Ji, A. (2014). Meta-analysis of methylcobalamin alone and in combination with prostaglandin E1 in the treatment of diabetic peripheral neuropathy. Endocrine, 46(3), 445-454.

  8. Liao, W. C., Wang, Y. J., Huang, M. C., & Tseng, G. F. (2013). Methylcobalamin facilitates collateral sprouting of donor axons and innervation of recipient muscle in end-to-side neurorrhaphy in rats. PloS one, 8(9), e76302.

  9. Xu, G., Lv, Z. W., Feng, Y., Tang, W. Z., & Xu, G. X. (2013). A Single-enter Randomized Controlled Trial of Local Methylcobalamin Injection for Subacute Herpetic Neuralgia. Pain Medicine, 14(6), 884-894.

Editor's Choice
Emails worth reading.

Once a week, we'll send you the most compelling research, stories and updates from the world of human enhancement.