Vitamin B12

Essential for nerve function and red blood cell production - deficiency is common, especially on metformin and in vegetarians.

What Vitamin B12 Measures

B12 is required for DNA synthesis, red blood cell production, and nerve myelination. Severe deficiency causes megaloblastic anemia and irreversible neurologic damage. Mild-to-moderate deficiency is common and often missed because the lab "normal" range starts at 232 pg/mL - but symptoms (fatigue, paresthesias, brain fog) can appear well above that threshold.

B12 is found almost exclusively in animal foods. Vegetarians and vegans need supplementation. Long-term metformin use depletes B12 absorption - ~30% of metformin users have low B12 after 5+ years. PPI users (omeprazole, etc) also have impaired absorption.

What Affects This Biomarker

B12 is influenced by: dietary intake (animal foods only - vegetarian/vegan diets without supplementation deplete it), absorption (intrinsic factor, healthy stomach acid required), age (absorption declines), pernicious anemia (autoimmune destruction of intrinsic factor), and pharmacologic agents - metformin lowers absorption; PPIs and H2 blockers lower absorption; supplementation (oral 500–1000 mcg daily, sublingual, or injection) restores reliably.

In the Context of Peptide Protocols

Test annually on metformin or PPI use, every 2–3 years otherwise. If low (<400) or borderline with symptoms, supplement methylcobalamin 1000 mcg daily, retest at 12 weeks. Pair with homocysteine - elevated homocysteine with low-normal B12 suggests functional deficiency. Critical to monitor on long-term GLP-1 + metformin combos.

Conditions That Track Vitamin B12

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