A recent study published in Annals of Neurology challenges the current understanding of vitamin B12 (B12) levels and their role in neurological health, suggesting that “normal” B12 levels may not be sufficient to prevent brain decline. The research, which employed a multimodal testing approach, investigates the relationship between B12 levels considered normal and neurological injury or impairment markers.
Vitamin B12 Deficiency
Vitamin B12, or cobalamin, is a crucial dietary vitamin obtained from animal products, certain dry fruits, nutritional yeast, and fortified foods. A deficiency in B12 can lead to various health issues, including blood abnormalities like megaloblastic anemia and neurological dysfunction, such as subacute combined degeneration of the spinal cord (SACD). SACD can cause sensory ataxia, paresthesia, and weakness, resulting from the degeneration of the myelin sheath and damage to the white matter of the spinal cord.
B12 deficiency is also linked to cognitive impairment, memory loss, dementia, and psychosis. Interestingly, vitamin B12 supplementation has been shown to slow brain atrophy in older individuals with mild cognitive impairment (MCI).
In the United States, B12 deficiency is typically defined as a blood level of less than 148 pmol/L, a threshold three standard deviations below the population average. However, there is no consensus on what constitutes “normal” B12 levels, with clinical features often serving as a more reliable indicator for supplementation.
The Study
This study, led by researchers from the University of California, San Francisco (UCSF) Memory and Aging Center, utilized visual evoked potentials (VEP) to assess the effect of low B12 levels on neurological function. VEP, particularly multifocal VEP (mfVEP), is a sensitive, non-invasive method to detect early changes in myelin function within the visual pathway.
The study involved 231 healthy individuals, with a median age of 71, who were part of the Brain Aging Network for Cognitive Health (BrANCH). Participants had their B12 levels measured and were tested annually for cognitive function, neurological health, and brain scans (MRI) to detect any signs of inflammation, axonal damage, or amyloid-related disease.
Study Findings
The study found that the cohort had a median blood B12 level of 415 pmol/L, with median values for Holo-TC (bioavailable B12) and Holo-HC (inactive B12) of 93 pmol/L and 298 pmol/L, respectively. Vitamin B12 levels were divided into above and below the geometric mean value of 408 pmol/L.
Key findings include:
Low Levels of Bioavailable B12: Low Holo-TC levels were associated with neurological dysfunction. Specifically, at lower B12 levels, there was a noticeable delay in nerve impulse conduction in the brain, as indicated by slower mfVEP latency.
Cognitive Function: Lower Holo-TC was linked to slower spatial processing speed, suggesting that inadequate bioavailable B12 contributes to brain dysfunction, particularly in older adults.
Non-Bioavailable B12 and Neurodegeneration: Increased Holo-HC levels correlated with elevated serum tau protein and ubiquitin C-terminal hydrolase L1 (UCH-L1), both of which are markers of neurodegeneration. High levels of inactive B12 may predict the development of neurofibrillary tangles, a hallmark of Alzheimer’s disease.
White Matter Damage: Low levels of bioavailable B12 were associated with larger volumes of white matter hyperintensities (WMH), even when blood B12 levels fell within the currently accepted “normal” range. This suggests that even normal levels of B12 may not prevent brain damage, particularly in the form of WMH.
Implications
The study reveals that low bioavailable B12 can lead to significant white matter injury in the spinal cord, possibly due to elevated homocysteine levels caused by B12 deficiency. While B12 supplementation can resolve hematological symptoms, it may not be effective in reversing neurological damage associated with B12 deficiency. This means that subtle neurological dysfunction can persist even in individuals with normal blood B12 levels.
The findings highlight the need for a reassessment of what constitutes optimal B12 levels. This research calls for revising nutritional guidelines to ensure that B12 levels not only prevent hematological issues but also support neurological health, particularly as we age.
You Might Be Interested In:
-
Early Gut Microbiota Linked to Food Sensitivities in Infants
-
New Therapeutic Cocktails Show Promise for Long-Lasting Asthma Relief
