Quick answer: Vitamin B12 deserves a closer look if you are over 50, take metformin or acid-blocking medication, eat little or no animal food, or have tingling in your hands or feet, brain fog, low mood, balance changes, or a rising MCV on your blood count. Serum B12 can look “fine” while methylmalonic acid (MMA) is already climbing, a sign your cells are not getting enough B12.
Key takeaways
Vitamin B12 deserves a closer look for adults over fifty, people on metformin or acid-blocking medicines, and those who eat little animal food.
B12 is essential for nerve insulation, healthy red blood cells and methylation.
Serum B12 can look normal while other markers such as MMA and homocysteine suggest a shortfall, so testing them together is helpful.
Who should consider vitamin B12?
Vitamin B12 is worth considering for adults over 50, since stomach acid and intrinsic factor decline with age, and for people taking metformin, proton pump inhibitors (PPIs) or H2 blockers. Vegans and vegetarians are another group, as are people with celiac disease, Crohn’s disease or a history of stomach or bowel surgery.
It is also worth a look for anyone with tingling or numbness in the hands or feet, balance changes, brain fog or low mood, and for people with a rising MCV (larger red blood cells) on a CBC.
Why B12 matters
B12 is essential for nerve insulation (myelin), healthy red blood cells, methylation, and energy metabolism. Methylation is the chemical “tagging” system cells use to turn genes on and off and to repair and copy DNA. Over a lifetime, these epigenetic tags tend to drift, and B12, folate and B6 are part of the nutrient support that keeps that system working. Absorption depends on stomach acid and intrinsic factor, both of which decline with age and with common prescriptions.
“Normal B12, abnormal you”
Serum B12 can sit in the normal range while methylmalonic acid (MMA) and homocysteine are already rising. That gap is where people get told they are fine and still feel anything but. When was your B12 last checked, and did anyone also look at MMA or homocysteine? More detail: vitamin B12 lab results explained.
Forms of B12
Methylcobalamin and hydroxocobalamin are the forms I prefer in most cases. Cyanocobalamin is the common, inexpensive form, and it works for many people. Injections are something some people need when the gut is not a reliable doorway, such as in pernicious anemia.
If you take metformin or a PPI, put B12 on your monitoring list. If you work with me, the B12 products I use are in my Fullscript dispensary. Related: who should consider methylfolate.
Safety
According to the NIH Office of Dietary Supplements, adults need 2.4 mcg of B12 a day, and no upper limit has been set because B12 has low potential for harm. Taking folic acid can hide the anemia of B12 deficiency while nerve damage progresses, so it is important to check B12 before or alongside folate.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you take metformin, a PPI or an H2 blocker long term, or if you have tingling, numbness, balance changes, brain fog or low mood. The same is true if your B12 is “normal” but you still have symptoms, or if you eat a plant-based diet and want to confirm your levels.
See a medical provider promptly for new numbness or weakness, trouble walking, confusion or memory loss that comes on quickly. These need prompt evaluation.
Told your B12 is “normal” but still do not feel right?
A free 15-minute consultation with Dr. Kneessi. No cost, no obligation. In-office in Odenton, MD or by telehealth.
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Should we check my MMA and homocysteine along with my B12 level?
Could vitamin B12 interact with any of my current medications or other supplements?
Would any labs or health history details help us decide whether vitamin B12 makes sense for me?
How would we tell whether vitamin B12 is a good fit for me, and when should we check in again?
Practitioner-grade options in my Fullscript catalog: if you and your clinician decide a supplement makes sense, my supplement guide by health goal links to the practitioner-grade products I trust.
Frequently asked questions
What are the signs of low B12?
Fatigue, tingling or numbness in the hands and feet, balance problems, brain fog, low mood, a sore tongue and anemia. Symptoms can develop slowly.
Which test is best for B12?
Serum B12 is a starting point. Methylmalonic acid (MMA) and homocysteine can show whether your cells are actually short on B12.
Does metformin lower B12?
Yes. Long-term metformin use is linked to lower B12 levels, so periodic testing is a good idea.
Is methylcobalamin better than cyanocobalamin?
Both can raise B12 levels. Many practitioners prefer methylcobalamin or hydroxocobalamin, and the choice can be tailored to you.
Sources
- Andrès E, et al. Vitamin B12 (cobalamin) deficiency in elderly patients. CMAJ 2004. PMID: 15289425. https://pmc.ncbi.nlm.nih.gov/articles/PMC490077/
- Lam JR, 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/
- Pawlak R, et al. How prevalent is vitamin B(12) deficiency among vegetarians? Nutr Rev 2013. PMID: 23356638. https://pubmed.ncbi.nlm.nih.gov/23356638/
- de Jager J, 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://pmc.ncbi.nlm.nih.gov/articles/PMC2874129/
- Green R, et al. Vitamin B12 deficiency. Nat Rev Dis Primers 2017. PMID: 28660890. https://pubmed.ncbi.nlm.nih.gov/28660890/
- NIH Office of Dietary Supplements: Vitamin B12 (Consumer Fact Sheet)
- MedlinePlus: Methylmalonic Acid (MMA) Test
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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