A Plant-Based Diet Provides No Natural B12
Vitamin B12 is made by microbes, not plants, so vegan diets lack it entirely.
- 0 mcg: B12 in plant foods (no reliable natural source)
- 2.4 mcg: Daily RDA (adult) (placeholder reference value)
- rising: Vegan diet prevalence (placeholder trend note)
- variable: Fortified food coverage (placeholder coverage estimate)
Why plants lack B12
B12 is synthesized by bacteria and archaea, not plant cells.
Common exposure gap
Unsupplemented vegans rely solely on prior body stores.
The Liver Holds a Finite B12 Reservoir
Liver stores buffer intake gaps for a limited number of years.
- 1-5 mg: Typical liver store (placeholder range)
- Liver: Store location (primary storage organ)
- years: Buffer duration (placeholder estimate)
- no intake: Depletion trigger (placeholder condition)
Storage physiology
Hepatocytes bind and hold B12 bound to transport proteins.
Why stores vary
Prior diet history sets each person's starting reserve size.
Stores Decline Gradually Across Years of No Intake
Depletion is slow, which delays symptom onset for years typically.
- ~0.5 mg/yr: Depletion rate (placeholder model rate)
- delayed: Symptom onset (placeholder timing note)
- subtle: Early signs (placeholder symptom note)
- blood test: Detection method (placeholder diagnostic)
Depletion curve shape
Reservoir falls roughly linearly per year of zero intake.
Why it is missed
Slow decline masks risk until stores run critically low.
Approaching the Deficiency Threshold Line
Below a critical reservoir level, deficiency symptoms begin appearing.
- 0.35 mg: Threshold level (placeholder model marker)
- rises sharply: Risk category (placeholder trend note)
- possible: Neurological risk (placeholder caution note)
- time-sensitive: Reversibility (placeholder note)
Threshold meaning
Below this line, functional deficiency symptoms typically emerge.
Monitoring importance
Periodic testing catches decline before symptoms appear.
Supplementation Refills the Reservoir and Prevents Risk
Regular B12 supplementation restores stores and avoids deficiency entirely.
- Supplement: Prevention method (oral or fortified source)
- 250-2000 mcg: Typical dose range (placeholder dose range)
- high: Effectiveness (placeholder efficacy note)
- all vegans: Recommended for (placeholder guidance)
Supplement strategy
Consistent dosing keeps reservoir levels safely above threshold.
Long-term outlook
Prevention is simple, cheap, and highly effective long-term.