Tiredness and nerve changes are easy to write off as getting older. Low vitamin B12 can cause both, and the symptoms can take several years to appear.[1] If you are over 50 or take certain medications, ask your clinician whether a B12 check makes sense before you assume it is age.
What low B12 can look like
The NIH Office of Dietary Supplements lists fatigue, neurological changes, megaloblastic anemia, palpitations and low red and white blood cell counts among the effects of B12 deficiency.[1] None of these is specific to B12. Persistent tiredness or nerve symptoms deserve a proper work-up, not a guess.
Who is more likely to run low
- Older adults. Depending on the definition used, 3% to 43% of community-dwelling older adults have deficiency based on blood levels, especially those with atrophic gastritis.[1]
- People on long-term metformin or acid-reducing drugs such as proton pump inhibitors, which can reduce B12 absorption.[1]
- People with pernicious anemia or other absorption problems, or who have had gastrointestinal surgery.[1]
- People who follow vegetarian or vegan diets, since B12 comes mainly from animal foods.[1]
What a new mouse study adds
A 2026 study in GeroScience gave aged female mice B12 supplements for 12 weeks. Compared with untreated mice, the supplemented animals had more mitochondria in their muscle, with better structure, and changes in proteins tied to energy production and oxidative stress.[2] Mitochondria are the parts of a cell that turn food into usable energy.
It is mouse data on supplementation and says nothing about deficiency or energy in people. It was done in female mice, not people, and the paper does not test whether supplements raise energy in people whose B12 is already normal.
What to do with it
- If you have ongoing fatigue, tingling, balance trouble or memory changes, ask your clinician to check your B12 along with a blood count.
- If you take metformin or an acid reducer long term, or eat little or no animal food, mention it when you ask. Those are the reasons the NIH fact sheet gives for lower B12.[1]
- Hold off on guessing with supplements or injections. Testing first tells you whether B12 is the problem and what kind of treatment fits.
- Do not stop or change a medication on your own because of this. Raise it with the clinician who prescribed it.
References
[1] National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. URL: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Finding as used: deficiency can cause fatigue, neurological changes, megaloblastic anemia, palpitations and low red and white blood cell counts, and symptoms can take several years to appear; causes include poor absorption, pernicious anemia, gastrointestinal surgery, prolonged use of metformin or proton pump inhibitors, and dietary deficiency; 3%-43% of community-dwelling older adults have deficiency depending on the definition used; vegetarian diets are another at-risk group. ↑︎
[2] Williamson AR, Yadav A, Ma W, Schmitt S, et al. Vitamin B12 improves skeletal muscle mitochondrial biology in aged mice. GeroScience, 2026. Population: aged female mice given 12 weeks of B12 supplementation or vehicle control. DOI: https://doi.org/10.1007/s11357-026-02264-1. Finding as used: supplementation increased muscle mitochondrial content and improved morphology; differentially expressed proteins were enriched in TCA cycle, oxidative phosphorylation and oxidative stress pathways. ↑︎
Kurt Greiner
Kurt is a digital strategist and IT professional blending emerging technology with practical application, exploring how individuals can leverage modern tools to navigate the second half of life with purpose.
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