Vitamin B12
MetabolismAlso known as: cobalamin, B12, Kobalamin
Vitamin B12 is a water-soluble vitamin essential for the production of red blood cells, the synthesis of DNA, and the healthy functioning of the nervous system.
It also supports brain function and energy metabolism. The body cannot make B12 on its own and relies on dietary sources such as meat, fish, eggs, and dairy. Excess B12 is stored in the liver, so deficiency can take time to develop but may lead to serious health issues if not addressed.
Reference range
Source: Ahead Health benchmark
Source: Ahead Health benchmark
Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider.
Why this matters
Low vitamin B12 can cause anemia with fatigue and weakness, along with neurological symptoms like tingling, balance problems, and memory difficulties. Severe deficiency may lead to irreversible nerve damage if untreated. Maintaining healthy B12 levels supports energy, cognition, and nervous system health.
How this connects to other biomarkers
- Low Vitamin B12 with elevated MCV (large red blood cells) and anemia points to megaloblastic anemia — the type of anemia caused by B12 or folate deficiency. Folic acid (Vitamin B9) deficiency causes the same picture and should always be checked alongside.
- Functional B12 deficiency is confirmed when Homocysteine is elevated, since B12 is needed to recycle homocysteine in the body.
- B12 deficiency can produce neurological symptoms (numbness, balance problems, memory issues) even when Hemoglobin is still normal — don't rely on a normal blood count to rule it out.
How often should I test Vitamin B12?
Most adults benefit from yearly vitamin B12 testing as part of a nutritional panel. Vegetarians, vegans, those over 60, and people on long-term PPIs or metformin should treat yearly testing as standard. After starting B12 supplementation or injections, retest at 1 to 3 months to confirm response.
At baseline / for screening: Once every 12 months from age 30 as part of a nutritional panel. More frequently if you're vegetarian or vegan, over 60, on long-term proton pump inhibitors or metformin, or have malabsorption.
When monitoring an intervention or change: Retest 1 to 3 months after starting B12 supplementation or injections. Pause supplements for 48 hours before testing, since recent doses can falsely elevate serum B12 and mask longer-term deficiency.
Note: Pause B12 supplements or injections for 48 to 72 hours before testing, since recent doses falsely elevate serum B12 and can mask longer-term deficiency. Retest at 1 to 3 months after starting therapy.
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