Quick answer: Vitamin B12 is needed for nerve health, red blood cells, DNA and energy. Low B12 can cause fatigue, numbness or tingling, memory problems and anemia. Common causes include a plant-based diet, older age, acid-blocking medications, metformin and pernicious anemia. Borderline results may be clarified with MMA and homocysteine tests.
Key takeaways
Vitamin B12 is needed for healthy nerves, red blood cells, DNA and energy.
Low B12 can show up as fatigue, numbness or tingling, memory changes or anemia.
Plant-based diets, older age, acid-blocking medications and metformin are common reasons for low levels, and MMA and homocysteine can clarify borderline results.
What is Vitamin B12?
Vitamin B12 (cobalamin) is a vitamin found in animal foods. It is needed for nerve insulation (myelin), red blood cell formation, DNA synthesis and methylation.
Why Vitamin B12 matters
Vitamin B12 matters for nerve and brain health, red blood cell production, energy metabolism, and methylation and homocysteine processing.
Understanding your result
Reference ranges vary by lab, age and sex. Your provider interprets your result against the lab’s range and your overall picture, rather than chasing a single number. Functional labs are optional. They can be helpful in more complex cases.
What low Vitamin B12 can mean
Low B12 can come with vegan or vegetarian diets, older age and low stomach acid, and acid-blocking medications and metformin. Pernicious anemia, gut conditions such as celiac disease, and weight-loss surgery can also lower it.
What high Vitamin B12 can mean
High B12 usually reflects supplements or injections, but it can also come with some liver or blood conditions, so follow up with your provider.
What affects Vitamin B12
B12 is affected by diet, stomach acid and intrinsic factor, medications, and gut health.
Ways to support healthy levels
Eat B12-rich foods such as meat, fish, eggs and dairy, and use supplements if you are plant-based or have absorption issues. Injections may be needed for pernicious anemia, and MMA and homocysteine are worth checking if results are borderline (see who should consider vitamin B12).
Vitamin B12 and healthy aging
B12 supports DNA synthesis, methylation and mitochondrial energy production. Deficiency can contribute to genomic instability, epigenetic changes and nerve damage, which is why B12 status matters more with age.
Related tests and articles: folate, ferritin.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have fatigue, numbness, tingling or memory changes, or if you are plant-based or over 60. The same is true if you take metformin or acid blockers, or have anemia or high homocysteine.
See a medical provider promptly for numbness, weakness, balance problems or confusion. B12 deficiency can cause lasting nerve damage if untreated.
What the research shows
Acid-reducing medicines are linked to low B12. In a 2013 JAMA study by Lam and colleagues, researchers compared 25,956 Kaiser Permanente members newly found to have low B12 with 184,199 members who were not. Two or more years of proton pump inhibitor use was linked to 65% higher odds of low B12 (odds ratio 1.65), and two or more years of H2 blockers to 25% higher odds. This was observational, so it shows a link rather than proof of cause.
Metformin has randomized trial evidence. In a 2010 trial by de Jager and colleagues, 390 people with type 2 diabetes who also used insulin took metformin 850 mg three times a day or a placebo for about 4.3 years. B12 fell 19% more on metformin, and the absolute risk of deficiency was 7.2 percentage points higher, about one extra case for every 14 people over four years. Because all participants also used insulin, results may differ for people on metformin alone.
Diet is the third big factor. A 2016 review by Pawlak and colleagues summarized studies that measured serum B12 in vegetarians and vegans and found that low B12 was common, especially in vegans and in people who did not use B12 supplements or fortified foods. Serum B12 alone can miss early deficiency, so the true rates may be higher, which is why methylmalonic acid (MMA) testing is sometimes added.
Vitamin B12 at a glance
| Topic | What the article explains |
|---|---|
| Why it matters | Nerve and brain health; red blood cell production; energy metabolism; and methylation and homocysteine processing |
| What can affect it | Diet; stomach acid and intrinsic factor; medications; and gut health |
| Supportive habits discussed | Eat B12-rich foods such as meat, fish, eggs and dairy; use supplements if you are plant-based or have absorption issues; injections may be needed for pernicious anemia; and check MMA and homocysteine if results are borderline |
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Since I take an acid blocker or metformin, should we check my B12 along with MMA or homocysteine?
How should I read my B12 alongside the rest of my labs and my symptoms?
How often would it make sense to recheck my B12 in my situation?
Which daily habits or medications could be influencing my B12 before we retest?
Frequently asked questions
What are symptoms of low B12?
Fatigue, numbness or tingling, memory problems, mood changes and anemia.
Can metformin lower B12?
Yes. Long-term metformin use is linked with lower B12.
What is MMA?
Methylmalonic acid is a test that rises when B12 is low at the tissue level.
Do vegans need B12 supplements?
Sources
- Lam JR, Schneider JL, Zhao W, et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 2013. PMID: 24327038. https://pubmed.ncbi.nlm.nih.gov/24327038/
- de Jager J, Kooy A, Lehert P, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ 2010. PMID: 20488910. https://pubmed.ncbi.nlm.nih.gov/20488910/
- Pawlak R, Lester SE, Babatunde T. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr 2016. PMID: 27381013. https://pubmed.ncbi.nlm.nih.gov/27381013/
- Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood 2017. PMID: 28360040. https://pubmed.ncbi.nlm.nih.gov/28360040/
- Atkinson M, Gharti P, Min T. Metformin use and vitamin B12 deficiency in people with type 2 diabetes. What are the risk factors? A mini-systematic review. touchREV Endocrinol 2024. PMID: 39526048. https://pmc.ncbi.nlm.nih.gov/articles/PMC11548349/
- Bailey RL, et al. Modeling a methylmalonic acid-derived change point for serum vitamin B-12 for adults in NHANES. Am J Clin Nutr 2013. PMID: 23803883. https://pmc.ncbi.nlm.nih.gov/articles/PMC3712554/
- MedlinePlus: Vitamin B12 Level
- NIH Office of Dietary Supplements: Vitamin B12 (Consumer Fact Sheet)
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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