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Healthy foods like salmon, seafood, vegetables, lean red meat and oats

Vitamin B12 and Mental Health: An Expert Series

By James Greenblatt, M.D.+

As a nutrient, vitamin B12 has several important roles, including contributing to the maintenance of healthy brain function. As a partner to folate, vitamin B12 is also important for transferring and supplying what are called “single carbon units” or methyl groups. Transferring methyl groups through the process of methylation is critical for the formation of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), neurotransmitters and the protective casing or sheath that surrounds nerve cells called myelin.


As a player in normal cognitive functioning, vitamin B12 has a role in supporting mental health. A deficiency in vitamins is known to be associated with low mood and cognitive A recent analysis even suggests that vitamin B12 supplementation may support positive mood, especially in those individuals that are.1


Along with potentially supporting emotional health, vitamin B12 can be critical for supporting healthy cognitive function. Studies on supporting cognitive health due to low vitamin B12 are prevalent in the published research.2 Due to these benefits, an international consensus statement published in 2018 recommends B-vitamin supplementation for maintaining brain health and cognitive function when appropriate.3


A mother and daughter smiling together


Part of the benefits of vitamin B12 for supporting normal brain function likely stem from its effects on homocysteine. Homocysteine is an amino acid formed in the body during normal functioning. Typically, levels of homocysteine are kept low by vitamins B12, folate and vitamin B6. However, if levels of these B vitamins are inadequate, homocysteine levels can build up.


Clinical studies show that vitamin B12 is vital in the metabolism of homocysteine. Vitamin B12 is required by the enzyme that converts homocysteine back to methionine.4 Vitamin B12, in combination with vitamin B6, folate, and betaine can provide a highly bioavailable combination of nutrients integral to maintaining healthy homocysteine metabolism and cardiovascular health.5


Another key factor in vitamin B12’s ability to support normal brain function is its role in neurotransmitter production. Vitamin B12, like folate, is needed for the production of serotonin, norepinephrine and dopamine. Standard for regular low mood often target these neurotransmitters. As such, serotonin is often described as the “feel good” neurotransmitter of the brain. By supporting production of these neurotransmitters, vitamin B12 plays a significant part in normal brain function.


Vitamin B12 is found in a number of foods, although mostly of animal origin, including liver, seafood, beef, dairy products and eggs. Vegetarians often do not get enough vitamin B12 and typically need to supplement the vitamin. For supplementation, the active forms of vitamin B12 are often preferred, including methylcobalamin and adenosylcobalamin, although hydroxycobalamin is readily converted as well.


As a nutrient, vitamin B12 plays a crucial role in normal brain function that supports mental health. Research suggests benefits that may be relevant for helping to support both healthy cognition and mood.


Importance of Vitamin B12 and the role in the maintenance of healthy brain function.


Ask The Expert


Should I take vitamin B12?


Dr Greenblatt- It depends. Having low B12 is quite common and while standard labs may help in identifying individuals who may need the vitamin, they don’t directly measure levels reaching the brain. Vegans and vegetarians typically need supplementation, and it likely should be considered for individuals in need of support for emotional wellbeing and cognition.


I am a vegan and heard seaweed is a good source of vitamin B12. Is that true?


Dr Greenblatt- Some data suggests that nori, a type of seaweed, shiitake mushrooms and soy yogurt might provide vitamin B12. However, studies of long-term consumption of these foods for maintaining adequate levels in humans have not been performed. It may be worth considering supplementation or the consumption of fortified foods to maintain adequate Vitamin B12 levels.


Does vitamin B12 support a healthy mood?


Dr Greenblatt- Vitamin B12 helps to maintain a normal mood. If a person is not consuming adequate vitamin B12, supplementation may be of benefit.


Can you get too much vitamin B12?


Dr Greenblatt- Vitamin B12 supplementation is typically well tolerated with minimal, or only mild, side effects. While there is no official upper limit of safety, there are cases of side effects from higher doses of the vitamin. Side effects can include feeling wired or excessive energy, headache, nausea, diarrhea, skin rash and fatigue. If you are taking high doses and think you are having side effects, stop supplementation and consult with your primary care doctor. In some cases, switching forms of the vitamin may reduce or eliminate concerns.


Meet Our Expert


Picture of James M. Greenblat

A pioneer in the field of integrative medicine, James M. Greenblatt, MD, has treated patients since 1988. After receiving his medical degree and completing his psychiatry residency at George Washington University, Dr. Greenblatt completed a fellowship in child and adolescent psychiatry at Johns Hopkins Medical School. Dr. Greenblatt currently serves as the Chief Medical Officer at Walden Behavioral Care in Waltham, MA and serves as an Assistant Clinical Professor of Psychiatry at Tufts University School of Medicine and Dartmouth College Geisel School of Medicine.


An acknowledged integrative medicine expert, educator, and author, Dr. Greenblatt has lectured internationally on the scientific evidence for nutritional interventions in psychiatry and mental illness. Through three decades of practice and research, Dr. Greenblatt is a leading contributor to helping physicians and patients understand the role of personalized medicine for mental illness. To learn more about the author, please visit


+Our Medical Consultants are retained advisors to Pure Encapsulations.




1. Borges-Vieira JG, Cardoso CKS. Nutr Neurosci. 2022;1-21. doi:10.1080/1028415X.2022.2031494


2. Sashindran VK, Aggarwal V, Khera A. Med J Armed Forces India. 2022;78(1):94-98. doi:10.1016/j.mjafi.2020.11.003


3. Smith AD, Refsum H, Bottiglieri T, et al. J Alzheimers Dis. 2018;62(2):561-570. doi:10.3233/JAD-171042


4. Halsted CH, et al. Proc Natl Acad Sci USA. 2002 Jul 23;99(15):10072-7.


5. O'Leary F, Samman S. Nutrients. 2010 Mar;2(3):299-316. doi: 10.3390/nu2030299. Epub 2010 Mar 5. PMID: 22254022; PMCID: PMC3257642.