Study suggests current vitamin B12 guidelines may not protect aging brain

The Story

A study from UC San Francisco published in *Annals of Neurology* found that healthy older adults with lower levels of active vitamin B12, even within the normal range, showed slower thinking, delayed visual processing, and more white matter damage on brain scans. The research involved 231 participants without dementia, with an average age of 71. The authors suggest current B12 deficiency definitions may be too broad for brain health and call for updated guidelines.

Key Facts

• The study was published in *Annals of Neurology* and led by senior author Ari J. Green, MD, of UCSF.
• Researchers enrolled 231 healthy participants through the Brain Aging Network for Cognitive Health (BrANCH) study; none had dementia or mild cognitive impairment.
• The average participant age was 71; average blood B12 level was 414.8 pmol/L, above the U.S. minimum cutoff of 148 pmol/L.
• The study focused on the biologically active form of B12 rather than total B12.
• After adjusting for age, sex, education, and cardiovascular risk factors, lower active B12 was linked to slower processing speed on cognitive tests, delayed visual responses, and a higher volume of white matter lesions on MRI.
• White matter lesions are areas of brain injury linked to cognitive decline, dementia, and stroke risk.
• Co-first author Alexandra Beaudry-Richard, MSc, stated that clinicians should consider supplementation in older patients with neurological symptoms even if B12 levels are within normal limits.
• The study does not prove that lower active B12 directly causes cognitive decline.
• A 2025 comprehensive review concluded that B12 deficiency remains a modifiable risk factor for neurological and cognitive problems.
• A 2025 systematic review and meta-analysis of randomized trials found a very small benefit in global cognitive function from B vitamin supplementation.
• A 2025 Mendelian randomization study using total serum B12 found no clear evidence of protection from psychiatric disorders or cognitive impairment in the general population.

Conflicting Reports

No conflicting reports identified in the source article.

Still Unclear

• Whether lower active B12 directly causes cognitive decline or is merely associated.
• Whether universal B12 supplementation is beneficial for all older adults.
• Whether current testing methods using total B12 miss people whose brains are already affected despite normal results.

Misconceptions

The article addresses the misconception that meeting the current minimum standard for vitamin B12 is sufficient to protect the aging brain. It also notes that the definition of B12 deficiency may be too blunt for brain health and that clear deficiencies are commonly associated with anemia, but subtle functional changes can occur without overt symptoms.

Key Figures

• Ari J. Green, MD – senior author, UCSF Departments of Neurology and Ophthalmology, Weill Institute for Neurosciences
• Alexandra Beaudry-Richard, MSc – co-first author, UCSF Department of Neurology and University of Ottawa
• Ahmed Abdelhak, MD, PhD – co-first author, UCSF Department of Neurology and Weill Institute for Neurosciences

Sources

• https://www.sciencedaily.com/releases/2026/05/260522031001.htm — Primary Source