Vitamin B12 and Brain Health: Memory, Nerves, Cognition

Regenerative and Vitality

May 23, 2026 · Dr. Andrew Vargas

Vitamin B12 is central to a healthy nervous system, to forming red blood cells, and to making DNA in new cells.

Your body cannot produce Vitamin B12, so you have to eat it and absorb it. Absorption can be impaired by autoimmune disease, by medications such as omeprazole and metformin, or simply by age-related changes in how the GI tract works.

Deficiency can be hard to correct with over-the-counter supplements. Intramuscular injections (vitamin "shots") are a standard route when levels need bringing up quickly.

Very low B12 can cause anaemia, and in more severe cases it impairs spinal cord function. Back in 2010, the VITACOG study reported that giving B vitamins to patients with mild cognitive impairment (MCI), which brings homocysteine down, appeared to slow how quickly cognitive impairment and dementia advanced.

So what actually counts as low?

The current threshold for B12 deficiency sits at roughly 150 picomoles per litre of blood, though recent work has questioned whether that is the right line.

A February 2025 study from UCSF researchers, published in the Annals of Neurology, suggested that unhealthy neurologic changes were occurring even at "normal" B12 values, where those values sat towards the lower end of the range.

A separate 2025 study from Boston University found that in middle-aged and older adults, higher average B12 levels were associated with slower cognitive decline, an effect size roughly equivalent to being six months younger.

Worried about your own risk of cognitive decline? Want to be tested or treated for B12 deficiency, or raise another vitamin concern? Our team at Ivy en Rose can help.

Reference

Smith AD, Smith SM, de Jager CA, Whitbread P, Johnston C, Agacinski G, Oulhaj A, Bradley KM, Jacoby R, Refsum H. Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial. PLoS One. 2010 Sep 8;5(9):e12244. doi: 10.1371/journal.pone.0012244. PMID: 20838622; PMCID: PMC2935890.

Beaudry-Richard, A., Abdelhak, A., Saloner, R., Sacco, S., Montes, S.C., Oertel, F.C., Cordano, C., Jabassini, N., Ananth, K., Gomez, A., Keihani, A., Chapman, M., Javvadi, S., Saha, S., Staffaroni, A., Songster, C., Warren, M., Boscardin, J.W., Kramer, J., Miller, B., Miller, J.W., Green, R. and Green, A.J. (2025), Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous System Injury in Older Adults. Ann Neurol, 97: 1190-1204.

https://doi.org/10.1002/ana.27200

Marino FR, Rogers G, Miller JW, et al. Higher vitamin B12 from mid- to late life is related to slower rates of cognitive decline. Alzheimer's Dement. 2025;21:e70864.