Current vitamin B12 guidelines may be insufficient to protect the aging brain, according to new research from UC San Francisco. Older adults with levels considered "normal" but on the lower end showed signs of slower thinking, delayed visual processing, and greater damage to brain white matter — the communication network linking different brain regions.
The Hidden Risks of 'Normal' B12
Published in Annals of Neurology, the study included 231 healthy participants (average age 71) from the Brain Aging Network for Cognitive Health (BrANCH) study. None had dementia or mild cognitive impairment. Their average blood B12 level was 414.8 pmol/L — well above the U.S. minimum of 148 pmol/L. However, the researchers measured active B12, the form the body can actually use, and found that even within the normal range, lower levels were linked to cognitive differences.
After adjusting for age, sex, education, and cardiovascular risk factors, participants with lower active B12 had slower processing speed on cognitive tests — an effect that grew stronger with age. They also showed delayed visual responses, indicating slower visual processing and reduced brain signaling efficiency. MRI scans revealed a troubling pattern: lower active B12 corresponded to a higher volume of white matter lesions, areas of injury linked to cognitive decline, dementia, and stroke risk.
Senior author Dr. Ari J. Green of UCSF Departments of Neurology and Ophthalmology noted that previous studies defining healthy B12 levels may have missed subtle functional changes. "Revisiting the definition of B12 deficiency to incorporate functional biomarkers could lead to earlier intervention and prevention of cognitive decline," he said.
Why Older Adults Are Especially Vulnerable
B12 absorption becomes less efficient with age, and factors like certain medications, digestive conditions, or low animal-based food intake can further reduce levels. Co-first author Alexandra Beaudry-Richard, MSc, emphasized that low but "normal" B12 may affect a much larger population than realized. "These levels could impact cognition to a greater extent than what we previously thought," she said.
What You Can Do
If you're over 60, consider asking your doctor to check your active B12 level — not just total B12. If levels are on the lower end, supplementation may be discussed. Eating B12-rich foods like fish, meat, eggs, and dairy, or fortified cereals, can help maintain healthy levels. However, always consult a healthcare provider before starting any supplement.
Source: ScienceDaily Mind & Brain
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