Are "Normal" Vitamin B12 Levels Harming Your Brain? What You Need to Know

Paula Gallagher on 02/27/2025

When it comes to brain health, most people recognize the importance of vitamins and minerals. However, new research suggests that even if your Vitamin B12 levels fall within the "normal" range, you could still be at risk for neurological changes.

A recent study published in the Annals of Neurology highlights the importance of bioavailable B12 (holotranscobalamin or Holo-TC) in maintaining white matter integrity and cognitive processing speed. This means that a standard B12 blood test may not tell the full story—ensuring your body has the right type of B12 is crucial for long-term brain health.

What Is Vitamin B12 and Why Does Your Brain Need It?

Vitamin B12, also known as cobalamin, is an essential nutrient that plays a critical role in:

Protecting nerve cells by maintaining the myelin sheath (the protective covering around nerves)
Aiding in red blood cell production to prevent anemia
Supporting cognitive function, memory, and focus
Regulating energy levels and mood balance

Since the human body cannot produce B12, we must obtain it from dietary sources, including:

🥩 Animal products (meat, fish, dairy, eggs)
🌱 Fortified plant-based foods (nutritional yeast, plant-based milks, cereals)
💊 Supplements (such as methylcobalamin or cyanocobalamin)

A B12 deficiency can lead to a range of health issues, from anemia and fatigue to neurological symptoms such as memory problems, numbness, and difficulty walking.

A deficiency in Vitamin B12 can lead to a range of health issues, including:

🔴 Megaloblastic anemia – A condition where red blood cells are larger than normal and function poorly

🔴 Subacute Combined Degeneration (SACD) of the spinal cord – A severe neurological disorder that causes loss of coordination (ataxia), tingling sensations (paresthesia), and muscle weakness

🔴 Cognitive impairment and memory loss – Linked to slower processing speed, difficulty concentrating, and brain fog

🔴 Mood disorders and psychiatric symptoms – Studies suggest that low B12 levels may contribute to depression, anxiety, and even psychosis in some individuals

SACD occurs when low B12 levels damage the myelin sheath—the protective covering of nerve fibers—leading to white matter destruction in the spinal cord. While this study focused on white matter damage in the brain, other research confirms that B12 deficiency can harm both the central and peripheral nervous systems.

Beyond the spinal cord, low B12 levels have been associated with cognitive decline, dementia risk, and brain atrophy. Interestingly, research shows that B vitamin supplementation may help reduce brain atrophy in older adults with mild cognitive impairment (MCI)—suggesting that maintaining adequate B12 levels could be beneficial for brain health as we age.

Why “Normal” B12 Levels Might Not Be Enough

B12 levels are typically measured in blood tests, with a deficiency defined as levels below 148 pmol/L in the U.S. However, this cutoff is widely debated because:

Many people experience neurological symptoms even within the “normal” range
Total B12 levels do not distinguish between active (Holo-TC) and inactive forms of B12
Low Holo-TC (bioavailable B12) is a better predictor of brain health than total B12

Active vs. Inactive B12: Why It Matters

When B12 is absorbed, it binds to two transport proteins:

Holo-Transcobalamin (Holo-TC): The active form of B12 that cells can actually use
Holo-Haptocorrin (Holo-HC): The inactive form, which does not directly contribute to cellular function

A standard B12 test measures both forms combined, which means some people may have "normal" total B12 but low bioavailable B12—putting them at risk for brain changes.

New Research: The Link Between B12 and Brain Health

A 2024 study conducted by researchers at the University of California, San Francisco (UCSF) Memory and Aging Center investigated the relationship between bioavailable B12 and white matter health in older adults.

Study Highlights:

231 healthy participants (median age: 71) underwent annual neurological testing and brain scans
Researchers measured Holo-TC levels (bioavailable B12) rather than total B12
MRI scans assessed white matter integrity, a key marker of brain health

Key Findings: Bioavailable B12 Matters

Participants with lower levels of Holo-TC (the bioactive form of B12) showed slower nerve conduction in the brain.
Lower bioavailable B12 was linked to decreased spatial processing speed, highlighting how even “normal” total B12 levels might not provide enough active B12 for proper brain function.
Older adults seemed to be at a greater risk of experiencing these subtle neurological effects, potentially due to reduced B12 absorption or naturally declining cognitive function.
Higher levels of Holo-HC, the inactive form of B12, were associated with increased serum markers of neurodegeneration, such as tau protein, which plays a role in the development of Alzheimer’s dementia.
Even within the normal B12 range, lower bioavailable B12 levels were correlated with increased white matter hyperintensity (WMH) volumes, a sign of white matter injury in the brain.

What Does This Mean for You?

The findings suggest that we need to rethink what constitutes “normal” B12 levels. Having a sufficient amount of bioavailable B12—not just total B12—is crucial for maintaining neurological health. Since traditional B12 supplementation often improves blood-related symptoms (like anemia) but not neurological symptoms, a more nuanced approach to diagnosis and treatment is needed.

How to Optimize Your B12 Levels

1. Focus on B12-Rich Foods

Animal sources – Lean meats, fish, eggs, dairy
Plant-based options – Fortified cereals, plant milks, nutritional yeast

2. Get the Right Blood Test

Ask your doctor for a Holo-TC test instead of just a total B12 test, especially if you are at risk (e.g., older adults, vegetarians, individuals with gastrointestinal issues).

3. Consider Supplementation

Methylcobalamin is a highly bioavailable form of B12 that may be beneficial for neurological function.

4. Address Absorption Issues

Certain conditions like pernicious anemia or gastrointestinal disorders, may impair B12 absorption. Treating these underlying issues may improve your B12 status.

Vitamin B12 is far more than just a nutrient for energy and red blood cells—it plays a critical role in brain health and neurological function. This study highlights the need for new, more precise guidelines that focus on bioavailable B12 (Holo-TC) rather than total B12 levels alone.

If you’ve been experiencing unexplained neurological symptoms like brain fog, memory issues, or tingling in your hands and feet, it may be time to take a closer look at your B12 status with your healthcare provider.

Book a Consultation to Optimize Your B12 Levels

Not sure if your B12 levels are supporting your brain health? Our wellness experts can help! Book a consultation today to get personalized guidance on nutrient optimization and cognitive support.

Frequently Asked Questions (FAQs)

1. What are the symptoms of low B12 levels?

Low B12 levels can cause fatigue, brain fog, memory loss, numbness or tingling in the hands and feet, balance problems, and mood changes. Severe deficiencies can lead to nerve damage and neurological disorders if left untreated.

2. Can I have B12 deficiency even if my blood test is normal?

Yes! A standard total B12 test does not distinguish between active (Holo-TC) and inactive B12. Some individuals with “normal” total B12 levels may still have insufficient bioavailable B12, leading to neurological symptoms.

3. How can I test for bioavailable B12?

Ask your doctor for a Holo-TC test (holotranscobalamin), which measures the active form of B12 that your body can use.

4. What’s the best form of B12 supplement?

Methylcobalamin is a highly bioavailable form of B12 that may be best for neurological support. Other effective forms include cyanocobalamin and hydroxocobalamin.

5. Can a vegan or vegetarian diet provide enough B12?

Since B12 is found mainly in animal products, vegans and vegetarians should consume fortified foods or take a B12 supplement to prevent deficiency.

6. How often should I check my B12 levels?

If you’re at risk (e.g., over 50, vegan, have digestive disorders, or take acid-reducing medications), check your B12 levels at least once a year.

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