Vitamin B12, also known as cobalamin, is a vital water-soluble vitamin that plays a crucial role in maintaining a healthy central nervous system, red blood cells, and nucleic acids such as DNA and RNA. According to the National Institutes of Health (NIH), individuals over 14 years old should consume 2.4 micrograms of B12 daily. Foods such as dairy, fish, meat, poultry, and eggs are rich in this vitamin, and fortified cereals, nutritional yeast, and supplements offer additional sources, making B12 deficiencies rare and affecting only about 3% of adults.
A new study, however, suggests that even within the normal range of vitamin B12, both low and high levels can impact cognitive function in older adults. Published in the Annals of Neurology, the study reveals that lower B12 levels may result in slower processing speed, while higher levels are linked to neurodegenerative biomarkers.
The Study’s Key Findings
The study, which was part of the Brain Aging Network for Cognitive Health at the University of California, San Francisco, enrolled 231 healthy older adults with an average age of 71.2 years. The researchers measured total B12 levels and holo-transcobalamin (active B12) levels, focusing on individuals whose B12 levels were within the normal range—except for two participants with a deficiency.
The researchers divided the participants into two groups: those with B12 levels below the mean (408 pmol/L) and those above it. They considered factors such as age, gender, cardiovascular risk, body mass index (BMI), the presence of the APOEε4 allele (which increases Alzheimer’s risk), HbA1C (a measure of blood glucose control), and education to analyze the results.
Lower Normal B12 Levels and Cognitive Impact
The study found that lower normal B12 levels were significantly associated with slower brain conductivity, as measured by multifocal visual evoked potentials (mfVEP). These findings were particularly evident in those with low levels of active B12. Additionally, participants with lower B12 levels exhibited slower processing speeds, a cognitive decline that worsened with age. They also had larger volumes of white matter hyperintensities, which are associated with cognitive impairment.
Dr. Ari J. Green, Chief of the Division of Neuroimmunology and Glial Biology at UCSF and lead author, stated that the study revealed multiple negative effects in individuals with lower B12 levels, which had long been considered within the adequate range. These effects included slower brain signal transmission, cognitive slowdown, and MRI evidence of white matter injury, particularly when considering the ‘active’ fraction of B12 (not routinely measured).
The Impact of Higher Normal B12 Levels
On the opposite end of the spectrum, the study also noted that higher B12 levels could negatively affect cognition. Participants with elevated B12 levels showed higher levels of T-Tau protein, a biomarker associated with neurodegeneration and dementia. This correlation was most prominent in individuals who had low levels of active B12 and high levels of holo-HC (inactive B12).
Dr. Clifford Segil, a neurologist at Providence Saint John’s Health Center in Santa Monica, CA, who was not involved in the study, suggested that further research is necessary to fully understand why these results were observed. Dr. Green also emphasized that high levels of inactive B12 could be linked to markers of axon injury. However, the researchers did not directly measure inactive B12 levels but rather calculated them from other measurements, which necessitates further study to determine the full implications.
Should Vitamin B12 Recommendations Be Revisited?
The findings of the study suggest that current B12 recommendations may need to be reconsidered, particularly for older adults. Dr. Green argued that B12 levels should not be assessed solely based on total blood B12, as it may not accurately reflect the bioavailable or active B12 levels in the body. A better approach would involve considering active versus inactive B12 levels, alongside assessments of neurological and cognitive function.
The study’s authors propose that low B12 levels could harm cognitive processes by affecting the integrity of the myelin that surrounds nerve cells. However, they did not investigate how these changes might occur. They also caution that elderly individuals may be especially susceptible to declining B12 levels and suggest that guidelines for optimal B12 levels should be reassessed for this vulnerable group.
In conclusion, this research calls for a reevaluation of the relationship between vitamin B12 and cognitive function, especially in older adults. Further studies are necessary to refine our understanding of B12’s role in brain health and to develop more tailored recommendations for maintaining cognitive function in aging populations.
