Vitamin B12 became personally important to me for reasons that go beyond general wellness. After years on multiple antiseizure medications, I learned that several of them — including some I’ve taken — can impair B12 absorption or deplete B12 over time. Add to that the fact that neurological conditions like epilepsy demand optimal nerve function, and B12 stops being a routine supplement consideration and becomes a specific clinical one. This post covers everything I’ve researched about it: what it does, how the body absorbs it, why deficiency happens, and what the evidence says about supplementation.
In This Article
What Is Vitamin B12?
Vitamin B12 (cobalamin) is an essential water-soluble vitamin required for nerve cell health, red blood cell formation, DNA synthesis, and brain function. The body cannot produce it and must obtain it from diet or supplements. It supports central nervous system myelination, red blood cell production, and DNA synthesis as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase enzymes. [NIH] Deficiency risks rise in vegans, older adults, and those with absorption issues — and notably, in people on long-term medications that affect the gut or stomach acid.
B12 Absorption Process
The body absorbs about 1–2 mcg per dose via intrinsic factor (IF)-mediated active transport, dropping to 1–2% at higher doses via passive diffusion. In the stomach, hydrochloric acid and pepsin release B12 from food proteins. The B12-IF complex then absorbs via receptors in the ileum, with the liver storing 50–90% of reserves. This multi-step process has several potential failure points — which is why so many people end up deficient without realizing it.
Factors Affecting Absorption
Healthy stomach acid, IF production, and intact ileum enhance uptake. Low stomach acid (common in older adults), PPIs, H2 blockers, metformin, antibiotics, gut issues (Crohn’s, celiac, SIBO), alcohol use, and pernicious anemia all impair absorption. Long-term use of multiple antiseizure medications has also been associated with B12 status changes in some individuals — worth monitoring with regular bloodwork if you’re on a complex medication regimen.
Natural Food Sources
Animal products provide reliable B12: beef liver (the richest source), clams, oysters, mussels, salmon, tuna, trout, sardines, egg yolks, and dairy. Plants lack true B12; vegans need supplements or fortified foods to prevent deficiency.
Types of B12 Supplements
Methylcobalamin and adenosylcobalamin are the most bioavailable active coenzyme forms. Hydroxocobalamin is a natural form that converts to active forms and is retained longer. Cyanocobalamin is synthetic, stable, and the most common form in inexpensive supplements, but requires conversion and contains trace cyanide in negligible amounts.
| Form | Key Benefits | Notes |
| Methylcobalamin | Direct use, brain/nerve support | Most preferred for daily use |
| Adenosylcobalamin | Energy/metabolism | Liver-stored |
| Hydroxocobalamin | Long retention | Preferred for injections |
| Cyanocobalamin | Stable, affordable | Requires conversion, contains trace cyanide |
💊 A Supplement Source I Trust
For the methylcobalamin and adenosylcobalamin forms discussed above, Vimergy is one of the few sources I trust for clean, well-absorbed formulations.
Deficiency Signs
Early: fatigue, weakness, brain fog, mood changes, depression, numbness and tingling. Severe: megaloblastic anemia, neuropathy, balance issues, vision problems, and increased dementia risk. Several of these symptoms overlap with neurological conditions, which can make deficiency harder to identify without bloodwork.
Dosage Guidelines
RDA: 2.4 mcg/day (higher during pregnancy: 2.6 mcg). For maintenance: 1,000 mcg oral daily. For deficiency correction: 5,000 mcg oral or 1,000 mcg intramuscular injection weekly, then monthly. For those with neurological conditions or absorption issues, liquid methylcobalamin and adenosylcobalamin forms taken on an empty stomach are generally considered most effective. Always work with your healthcare provider to determine appropriate dosing for your situation.
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Sources & References:
- Vitamin B-12 – Mayo Clinic
- Vitamin B12 – NIH Health Professional Fact Sheet
- Vitamin B12 – Harvard Nutrition Source
- Vitamin B12 Deficiency – StatPearls/NCBI
- Methylcobalamin vs Cyanocobalamin – Healthline
Disclaimer
This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before making any changes to your health regimen, including medications, diet, exercise, or supplementation. David Julian, Natural Vitality Advocate, is not a licensed medical professional. Views expressed are personal and based on lived experience — they do not guarantee specific outcomes. David Julian is not affiliated with Natural Vitality or NaturalVitality.com.