Vitamin B12 (Cobalamin)
An essential vitamin for nerve function, DNA synthesis, and red blood cell formation. Deficiency is common and often missed.
What is Vitamin B12?
Vitamin B12, also called cobalamin, is an essential water-soluble vitamin that your body cannot produce. You must get it from food or supplements.
B12 plays critical roles in:
- Nerve function — Maintains the myelin sheath protecting nerves
- DNA synthesis — Required for cell division
- Red blood cell production — Prevents a type of anemia
- Energy metabolism — Helps convert food to energy
Unlike most vitamins, B12 is stored in the liver for years, so deficiency develops slowly — but it can cause lasting damage if untreated.
Normal Ranges
| Level | Interpretation |
|---|---|
| Above 400 pg/mL | Optimal |
| 200–400 pg/mL | Low-normal (may have symptoms) |
| Below 200 pg/mL | Deficient |
Many experts consider the "normal" lower limit of 200 pg/mL too low. Symptoms can appear at levels considered technically normal.
Why It Matters
Neurological Health
B12 deficiency damages the nervous system, causing:
- Numbness and tingling in hands and feet
- Balance problems
- Memory issues and brain fog
- Depression and mood changes
Nerve damage can become permanent if deficiency persists.
Energy and Fatigue
Unexplained fatigue is one of the earliest and most common symptoms of B12 deficiency.
Anemia Prevention
Severe B12 deficiency causes megaloblastic anemia — abnormally large, dysfunctional red blood cells that can't carry oxygen efficiently.
Who's at Risk for Deficiency
- Vegetarians and vegans — B12 is only found naturally in animal products
- Adults over 50 — Absorption decreases with age
- People with digestive conditions — Crohn's, celiac, gastric bypass
- Those taking certain medications — Metformin, PPIs (acid reducers)
- Heavy alcohol users — Impairs absorption
Symptoms of Deficiency
Early Signs
- Fatigue and weakness
- Pale or yellowish skin
- Mouth ulcers
Progressive Signs
- Numbness or tingling (paresthesia)
- Difficulty walking
- Cognitive changes
- Depression
Food Sources
- Liver and organ meats
- Shellfish (clams, mussels)
- Fish (salmon, trout, tuna)
- Meat and poultry
- Eggs and dairy
- Fortified foods (cereals, nutritional yeast, plant milks)
How Often to Test
- Vegetarians/vegans: Annually
- Over 50: Every 2–3 years
- Taking PPIs or metformin: Annually
- Unexplained fatigue or neurological symptoms: Check immediately
Related Biomarkers
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