Vitamin B12 is an essential nutrient for energy in our cells.
It fuels our brain, our nerves and muscles!
The problem with testing is:
Even if our blood B12 levels are fine, the levels in our brain and tissues are often low.
This is because even with supplements, our body can block B12 from our reaching tissues and brain.
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This can be especially critical for anyone with long COVID, PANS, autism, or any neuroinflammatory condition.
Kids with autism often have notable speech gains with higher dose supplementation and patients with crushing fatigue or nerve damage can heal in weeks!
My daughter and I experienced these tremendous outcomes from increasing B12 – we’ll share what we take near the end of the post.
SKIP TO: Our Dosing & Purchasing
Some of the many symptoms are:
Symptoms of Cerebral B12 deficiency
Cognitive: Memory loss, difficulty concentrating
Neurological: Numbness, tingling, pins and needles, muscle weakness, problems with balance and coordination, POTS look-alike symptoms, difficulties speaking / word recall
Psychological: Depression, anxiety, and irritability
Whole body: anemia, fatigue, low muscle strength
It’s similar in concept to Cerebral Folate Deficiency (CFD) but for B12
7 ways vitamin B12 gets blocked from reaching your brain and tissues:
1. Blood-Brain Barrier
Even if B12 reaches your blood, the blood-brain barrier can be stingy.
Inflammation or oxidative stress may tighten this barrier, blocking B12 from brain tissue.
Aging worsens this, slowing nutrient delivery.
2. Receptor Roadblocks – Recently discovered!
There’s a newly identified condition called Autoimmune B12 Central Deficiency (ABCD)
The first patient presented with progressive tremor, ataxia, and speech problems.
They found her CD320 was being attacked by autoantibodies.
CD320 is a protein that transports B12 across the blood brain barrier.
It’s especially necessary for getting B12 into the cerebrospinal fluid (CSF), where your brain can use it for myelination (insulating nerve fibers) and other vital processes.
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Studies link CD320 issues to neurological deficits, even with normal blood B12 levels.
It’s been found that approximately 20% of people with neurological conditions have autoimmune antibodies attacking CD320, severely limiting B12 levels in the brain.
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What can be done?
In the study, “Transcobalamin receptor antibodies in autoimmune vitamin B12 central deficiency” (published 6/26/24) they found:
High serum B12 concentrations may suffice to overcome BBB transport defects caused by anti-CD320.
So there’s hope!
See below for the amount of B12 we take to overcome this potential issue.
3. Gut Gatekeepers Fail
Your stomach needs the intrinsic factor protein to carry B12 through your intestines.
Autoimmune conditions including pernicious anemia can destroy intrinsic factor production, meaning the B12 simply gets flushed out.
4. Transport Troubles
Transcobalamin (TC) is a protein that binds to and transports B12, from the bloodstream to cells throughout the body.
Newly absorbed B12 bound to transcobalamin (TC) circulates to the liver and to the rest of the organs.
Genetic mutations or low TC levels mean B12 has no ride and can’t reach tissues.
5. Liver Lockout
Our liver stores B12, but inflammation or liver disease can impair its release.
This leaves B12 trapped, unavailable for brain or tissue use.
6. Microbe Thievery
Gut bacteria or parasites can steal B12 before it’s absorbed.
High-folate vegan diets can hide B12 deficiency, letting tissue starvation go unnoticed for longer.
7. Drug Disruptors
Medications like metformin or PPI’s can sabotage B12 absorption.
Long-term use? Your gut’s ability to grab B12 might be crippled even if you’re supplementing.
Why Blood Tests Lie
Serum B12 tests measure total B12 in blood, not what’s active or reaching tissues.
You could still be starving at the cellular level.
Better tests:
Transcobalamin-bound B12 (holotranscobalamin) is what matters, but standard tests often miss this.
HoloTC measures the active form of vitamin B12 bound to transcobalamin. Normal levels indicate sufficient active B12. Low levels may suggest early B12 deficiency, even before other markers like total B12 show abnormalities.
Methylmalonic acid (MMA) or homocysteine tests are better markers of functional deficiency, but they’re not routine.
Elevated levels can suggest a B12 deficiency.
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High-Dose Supplements to the rescue
It’s a critical first step to try higher doses of B12 to compensate for the above issues.
The dosing can depend on the method.
Sublingual will require more than injections
Often people use 5,000 – 10,000 IU per day sublingually.
Sublingual dosing is very affordable and will indicate if you are deficient.
The preferred, bioavailable forms are: Hydroxocobalamin, Methylcobalamin, Adenosylcobalamin (not cyanocobalamin)
If it’s going to help, you should notice more energy on the first day.
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B12 can bring SIGNIFICANT improvements – it did for me and my blood levels were not low.
I like to divide my dosing throughout the morning because all at once can be too much.
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Note: It can be important to take it with additional folate (not folic acid) to enhance absorption.
Other B vitamins, especially B6 (P5P) are often recommended so your B’s don’t get out of balance.
We find that a multivitamin is sufficient to avoid issues.
these are all at Whole Foods
Our supplements: Brand & Dosing
I take approximately 5,000 IU / mcg sublingually and 100 IU / mcg via injection per day.
100 mcg is very low for injections, you will probably want to use more! At least initially.
My daughter takes only 1-2,000 mcg sublingually per day because with more than that, she has trouble sleeping (too much energy).
Here is the Liquid we use
Here are the Lozenges we use (with methylfolate)
An easy way to get B12 injections
As you continue with supplementing, you may wish to try injections (I get mine from AgelessRX)
It’s very simple.
They provide a free “online visit” which is simply a questionnaire and uploading of drivers license and photo.
Then they send the order to a compounding pharmacy and ship to you!
Here’s the link to AgelessRX (choose all treatments from menu at top right)
The discount code: VITAL15 will give you 15% off
Can I take too much?
Because it’s water soluable, what we don’t use is flushed from our body.
Giving our blood enough B12 to force across defective CD320 receptors or tight blood-brain barriers can restore function.
The sheer volume of high doses can also push B12 into cells without relying on faulty intrinsic factor or transcobalamin.
For pernicious anemia, lifelong injections or megadoses are standard.
Consistency is key—tissues need sustained saturation.
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Ok to be “in the blue”
Being in the blue — aka texting someone who seems to be ignoring or ghosting you over, and over, and over, until they finally break down, is ok here!
Not advised in dating, but very valuable for B12!
If B12 were texting our body it might go a little something like this:
Press on!
Your memory issues, concentration, difficulties speaking / word recall, numbness, tingling, pins and needles, muscle weakness, problems with balance and coordination, POTS symptoms, depression, anxiety, irritability, anemia, fatigue, muscles and more — will thank you! 💪🏼
Disclaimer: this post is not medical advice.
I am NOT an Amazon affiliate and this post is not sponsored.
If you have concerns about using methylated vitamins, please see this page: Who should avoid methylated B12 and 5-MTHF and why?
Learn more about each of the Supplements we use in this post:
Diary of Recovery 