lab metric
Vitamin B12
Table of contents
Description
Vitamin B12 is a water‑soluble vitamin that supports red blood cell production, neurologic function, and DNA synthesis. Because your body can store B12 for years, a low result often reflects a longer-term issue with intake or (more commonly) absorption rather than what you ate this week.
Why it matters
B12 deficiency can contribute to fatigue, anemia, cognitive changes, numbness/tingling, and balance issues. It’s also tightly linked to folate metabolism and homocysteine—so a “borderline” B12 can still matter if symptoms or homocysteine are elevated.
Common reasons B12 runs low
Low intake (strict vegan diet without supplementation)
Reduced stomach acid or intrinsic factor (pernicious anemia)
GI conditions affecting absorption (celiac, Crohn’s, bariatric surgery)
Medications that reduce absorption (metformin, long‑term PPIs/H2 blockers)
When B12 is high
High B12 is often from supplementation or injections. Less commonly, it can be seen with liver disease, kidney dysfunction, or certain inflammatory/hematologic conditions—context and trend matter.
Educational only, not medical advice. If B12 is low or symptoms are present, review results with a clinician; follow-up often includes MMA (methylmalonic acid), homocysteine, folate, and a plan for repletion plus repeat testing.
Frequently Asked Questions
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