Meeting the minimum requirement for vitamin B12—a crucial nutrient for DNA synthesis, red blood cell production, and nerve function—may not be sufficient, especially as we age. In fact, new research suggests that even levels within the so-called “normal” range could increase the risk of cognitive decline.
A study led by researchers at UC San Francisco found that older adults with lower—but still normal—B12 levels exhibited neurological and cognitive deficiencies. These individuals showed signs of damage to the brain’s white matter, which is responsible for communication between different brain regions. Additionally, their cognitive test scores reflected slower thinking and visual processing speeds compared to those with higher B12 levels.
The findings, published on February 10 in Annals of Neurology, raise important questions about current B12 guidelines. According to the study’s senior author, Dr. Ari J. Green of UCSF’s Departments of Neurology and Ophthalmology and the Weill Institute for Neurosciences, the recommended thresholds for B12 intake may be outdated.
“Previous studies may have overlooked subtle yet meaningful effects of B12 levels on cognitive function,” said Green. “While severe B12 deficiency is well known for causing anemia, our research suggests that even milder deficiencies—within the normal range—could contribute to cognitive decline. Updating the definition of B12 deficiency to include functional biomarkers could enable earlier interventions.”
The Link Between B12, Cognitive Function, and Brain Lesions
For the study, researchers examined 231 healthy adults with an average age of 71, all of whom had no diagnosed dementia or mild cognitive impairment. Participants were recruited through UCSF’s Brain Aging Network for Cognitive Health (BrANCH) study.
Their average blood B12 concentration was 414.8 pmol/L—well above the U.S. minimum of 148 pmol/L. To better understand B12’s impact, researchers analyzed its biologically active component, which is a more precise measure of the vitamin’s availability in the body.
The results were striking: those with lower active B12 levels demonstrated slower cognitive processing, an effect that worsened with age. They also showed delays in responding to visual stimuli, indicating a general slowdown in brain function. MRI scans further revealed a higher volume of lesions in their white matter—changes that have been linked to dementia, cognitive impairment, and stroke.
A Potentially Widespread Issue
Although the study focused on older adults, co-first author Alexandra Beaudry-Richard, MSc, believes the implications could be broader. “Lower B12 levels may impact cognitive function more significantly than previously thought and could affect a larger proportion of the population than we realize,” she said. Beaudry-Richard is completing her doctorate at UCSF’s Department of Neurology and the University of Ottawa’s Department of Microbiology and Immunology.
She suggests that clinicians consider B12 supplementation for older adults experiencing neurological symptoms, even if their levels fall within the normal range. “Ultimately, we need to invest in more research to understand the biology of B12 insufficiency. It may be a preventable cause of cognitive decline,” she added.
The Takeaway: Time to Reevaluate B12 Guidelines?
This study underscores the need to reassess current B12 recommendations, particularly for older adults. While traditional deficiency thresholds are based on overt symptoms like anemia, the new findings suggest that more subtle neurological effects may appear long before severe deficiency sets in.
If you’re concerned about cognitive health as you age, it may be worth discussing B12 levels and potential supplementation with your healthcare provider. Ensuring adequate B12 intake could be a simple yet powerful way to protect your brain and maintain cognitive function over time.
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