Why We Need To Rethink What’s “Normal” Vitamin B12 for Brain Health
Vitamin B12 is essential for keeping your blood, nerves and brain healthy. When you don’t have enough, it can lead to problems like fatigue, weakness, numbness, and memory issues. The real danger of low B12 levels may be hidden in plain sight—long before these overt signs appear. A new study from the University of California suggests that the effects of low B12 may start even before these overt symptoms appear and current B12 thresholds may be missing subtle but significant brain changes that could lead to cognitive decline.
What the Study Found
The research, published in Annals of Neurology, examined 231 older adults with blood B12 levels considered “normal” by today’s standards. Using advanced testing- including brain imaging and cognitive function assessments and nerve conduction studies- researchers discovered something surprising — even in this supposedly healthy range, lower levels of B12 were linked to signs of brain aging.
Why This Matters
People with lower active B12 (holo-transcobalamin) had slower brain processing speeds such as slow thinking and memory recall and more damage to the brain’s white matter, which helps your brain cells communicate.
Some forms of B12 in your blood may give a false sense of security, suggesting you have enough when your brain could actually be struggling. Intriguingly, high levels of inactive B12 (holo-haptocorrin) correlated with biomarkers of neurodegeneration, raising questions about whether certain forms of B12 in the blood might be misleading indicators of sufficiency.
Why “Normal” B12 Levels Might Not Be Enough
Doctors usually say you have a vitamin B12 deficiency if your blood levels are very low, typically below 148 pmol/L. But new research suggests that even if your B12 levels are technically “normal,” your brain could still be at risk.
The current tests we use today might miss early signs of brain damage caused by low B12. According to Dr. Ari J. Green, one of the researchers, these tests don’t always catch the small but important changes happening in the brain. Without obvious symptoms like extreme fatigue or numbness, people may assume they’re fine — but their brain health may already be declining.
Dr. Green suggests “Revisiting the definition of B12 deficiency to incorporate functional biomarkers could lead to earlier intervention and prevention of cognitive decline”. This underscores the importance of using additional tests to check for subtle signs of damage, which could help doctors treat problems earlier.
Should More People Take Vitamin B12 Supplements?
Traditionally, B12 deficiency has long been treated with B12 supplements or injections. But this study suggests that even those with “borderline” B12 levels might benefit from taking B12 supplements to protect their brain health.
Co-author Alexandra Beaudry-Richard, MSc., recommends that doctors consider B12 supplements for older adults experiencing memory issues or neurological symptoms — even if their B12 levels appear normal.
Who’s at Risk for Low B12?
Certain groups of people are more likely to have low B12 levels. Up to 20% of older adults may have low B12, even if blood tests seem normal.
Vitamin B12 is mostly found in animal food such as meat, fish, eggs, and dairy, so people on plant-based diets such as vegetarians are at a higher risk for deficiency.
People with impaired nutrient absorption associated with digestive conditions like gastritis or Crohn’s disease that prevent proper B12 absorption, are particularly vulnerable to B12 insufficiency.
If you fall into one of these groups, regular B12 checks and supplementation may help protect your brain.
Take Action for Your Brain Health
This study is a wake-up call with clear implications.
It may be time to rethink how we treat B12 deficiency.
With growing evidence linking low B12 levels to neurolgical decline, timely B12 supplementation – especially in older adults – could be a simple yet effective strategy to maintain brain health.
Don’t wait for severe symptoms like memory loss or numbness before considering B12 supplements. If you notice signs like brain fog, memory lapses, unexplained fatigue or tingling in your hands or feet
It may be worth discussing a B12 test with your doctor. Taking a simple supplement could be a proactive step to keep your brain sharp and healthy as you age.
When it comes to protecting brain health, early action is key. Waiting for overt symptoms may already be too late.
References:
1. Beaudry-Richard A, Abdelhak A, Saloner R, et al. Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous System Injury in Older Adults. Ann Neurol. Published online February 10, 2025. doi:10.1002/ana.27200
2. Leigh, S. ‘Healthy’ Vitamin B12 Levels Not Enough to Ward Off Neuro Decline. UCSF News, 18 Feb. 2025, https://www.ucsf.edu/news/2025/02/429491/healthy-vitamin-b12-levels-not-enough-ward-neuro-decline.
