Here's What You Should Know
Vitamin B12 is required for three foundational processes: DNA synthesis, red blood cell formation, and myelin sheath integrity — the protective coating around nerve fibers that makes nerve signals fast and reliable. When B12 is low, all three break down. The challenge is that deficiency develops slowly, symptoms are non-specific, and serum B12 on a standard blood panel is a notoriously poor predictor of functional deficiency. You can have B12 "in range" and still be functionally depleted.
Functional deficiency is better caught by methylmalonic acid (MMA) and homocysteine — both accumulate when B12 is truly insufficient at the cellular level. Many people with chronic fatigue, neurological symptoms, and mood disorders never get these tested.
Signs This May Be Part of Your Pattern
- Fatigue and weakness that doesn't respond to sleep
- Tingling, numbness, or burning in hands or feet
- Cognitive fog, memory gaps, difficulty concentrating
- Low mood, depression, or emotional flatness
- Inflamed or sore tongue (glossitis)
- Pale or slightly jaundiced skin
- Unsteady gait or balance problems (in advanced deficiency)
Why This Gets Missed
Animal products are the primary dietary source, so strict vegans and vegetarians are at structural risk. But most people who are B12 deficient eat meat — the deficiency comes from absorption failure, not dietary lack. Intrinsic factor (produced in the stomach) is required to absorb B12 from food. Anything that damages the stomach lining — atrophic gastritis, H. pylori infection, long-term PPI use — reduces intrinsic factor and blocks absorption. Age also reduces intrinsic factor production naturally.
How It Connects to the Bigger Pattern
Metformin is the most common medication driver of B12 depletion — it blocks absorption in the ileum and the effect is dose- and duration-dependent. Omeprazole (and all PPIs) deplete B12 by suppressing stomach acid needed for food-bound B12 release. Oral contraceptives lower B12 through unclear mechanisms. H2 blockers (famotidine, ranitidine) also impair absorption.
B12 works in close partnership with folate and B6 in the methylation cycle. Deficiency in any one stalls the others. The MTHFR C677T gene variant further complicates methylation and increases B12 requirements. Active forms — methylcobalamin and adenosylcobalamin — bypass conversion steps that some people cannot perform efficiently.
What to Start With
For dietary access, B12 from animal products (meat, fish, dairy, eggs) is the primary source. Supplemental B12 in high-dose oral form (1000 mcg) can be absorbed passively even without intrinsic factor — the mechanism is different from food-bound absorption. Sublingual and injectable forms bypass digestive absorption entirely and are preferred for absorption conditions. If metformin or PPI use is driving the depletion, the supplement dose needs to be maintained continuously rather than episodically.