Even “Normal” Vitamin B12 May Not Be Enough to Protect the Aging Brain
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Even “normal” levels of vitamin B12 may not be enough to protect the aging brain. UCSF researchers found that older adults with lower, but still technically normal, B12 showed slower processing speeds, more white matter damage, and cognitive weaknesses.
When “Normal” Vitamin B12 May Not Be Enough
Meeting the standard daily requirement for vitamin B12, which is essential for making DNA, red blood cells, and nerve tissue, may not provide enough protection for the brain, particularly in older adults. Actually,falling within the “normal” range could still increase the risk of cognitive problems.
Researchers at UC San Francisco studied healthy older adults and discovered that participants with lower B12 levels, even though still considered normal, showed neurological and cognitive weaknesses. These individuals had more damage in the brain’s white matter (the network of nerve fibers that allows different regions of the brain to communicate) and scored lower on tests measuring cognitive speed and visual processing compared with those who had higher B12 levels.
The study was published in Annals of Neurology.
Rethinking Vitamin B12 Guidelines
According to senior author Ari J. Green, MD, of UCSF’s Departments of Neurology and Ophthalmology and the Weill Institute for Neurosciences, the results raise concerns about whether current B12 recommendations are sufficient and suggest that guidelines may need to be revised.
“Previous studies that defined healthy amounts of B12 may have missed subtle functional manifestations of high or low levels that can affect people without causing overt symptoms,” said Green,noting that clear deficiencies of the vitamin are commonly associated with a type of anemia. “Revisiting the definition of B12 deficiency to incorporate functional biomarkers could lead to earlier intervention and prevention of cognitive decline.”
Vitamin B12 is a nutrient that the body cannot make on its own, so it must come from diet or supplements. The richest sources are animal products like meat, poultry, fish, eggs, and dairy.
Vitamin B12 Deficiency May Be Underestimated, Leading to Cognitive Decline in Older Adults
New research suggests current guidelines for vitamin B12 deficiency may be inadequate, potentially leading to preventable cognitive decline in older adults. A study published in February 2025 in Annals of Neurology found an association between even low-normal vitamin B12 levels and markers of central nervous system injury.
Researchers, led by Alexandra Beaudry-Richard from the Department of Neurology and the Department of Microbiology and Immunology at the University of Ottawa, and co-first author Ahmed Abdelhak, MD, PhD, of the UCSF Department of Neurology and the Weill Institute for Neurosciences, advocate for a re-evaluation of current B12 deficiency thresholds. They suggest clinicians should consider supplementation in older patients experiencing neurological symptoms, even if their B12 levels fall within the traditionally accepted “normal” range.
“Ultimately, we need to invest in more research about the underlying biology of B12 insufficiency, as it might potentially be a preventable cause of cognitive decline,” Beaudry-Richard stated.
The study, titled “Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous system Injury in Older adults,” https://doi.org/10.1002/ana.27200 examined the relationship between B12 levels and indicators of neurological damage. Since its publication, the findings have generated significant discussion within the medical community.
Several reviews have reinforced the link between low-normal B12 and subtle neurological damage, suggesting current guidelines may underestimate the brain’s actual B12 requirements. Experts are now calling for a revised cutoff for deficiency and a shift towards measuring biologically active B12 – specifically, holo-transcobalamin – rather than relying solely on total serum B12 levels.
This is because even “healthy” total serum levels may not reflect sufficient active B12 available to the brain, leaving older adults vulnerable to cognitive decline and white matter damage. Emerging evidence also points to a connection between low active B12 and elevated levels of neurodegeneration markers, such as tau protein, further supporting the need to redefine adequate B12 levels.
The research was funded by the westridge Foundation and the Canadian Institutes of Health and Research. The authors report no conflicts of interest.
Authors: Ahmed Abdelhak, MD, PhD (UCSF Department of Neurology and the Weill Institute for Neurosciences) and Alexandra Beaudry-Richard, and a full list of authors can be found in the original study.
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