Fatigue gets written off as a normal part of getting older more often than it should. New 2026 research suggests one overlooked reason might actually be vitamin B12, and not just in the way most people think.
What The Research Shows
The traditional understanding is that B12 deficiency causes fatigue through anemia, without enough B12, the body produces oversized, immature red blood cells that carry oxygen less efficiently. That’s real and well established. But 2026 research led by scientists at Cornell and the University of Alabama at Birmingham found something more specific, B12 deficiency appears to interfere with the DNA inside mitochondria, the structures inside cells that generate energy, reducing energy production directly at the cellular level, separate from any effect on red blood cells.
This matters because it may explain why some people report fatigue before standard blood tests show obvious anemia. A related 2026 study in aged mice found that B12 supplementation improved several markers of mitochondrial health in muscle tissue.
Separately, a large 2026 study out of Osaka Metropolitan University followed around 600 healthy adults and found that lower B12 and folate levels correlated with higher homocysteine, which was in turn linked to greater self reported fatigue and lower motivation.
Who’s Actually At Risk
Deficiency risk increases with age due to reduced stomach acid production, which is needed to absorb B12 from food. Certain common medications, including metformin, are also associated with lower B12 levels in older adults. One 2025 study found B12 deficiency in nearly 30 percent of older adults taking metformin long term.
What This Doesn’t Mean
Current research does not support using B12 supplements or injections to boost energy in people whose levels are already normal. Researchers are consistently clear on this point, more B12 doesn’t mean more energy for someone who isn’t deficient. The right first step is testing, not guessing.
Sources
- Vitamin B12 Deficiency Can Mimic Aging, Newsweek, 2026
- Associations of Plasma Homocysteine Reflecting Vitamin B12 and Folate Status with Fatigue-Related Outcomes in Healthy Adults, Nutrients, 2026
- Vitamin B12 deficiency in metformin-treated community-dwelling older adults with diabetes, Journal of Pharmacy Practice and Research, 2025
Can B12 supplements boost my energy if my levels are already normal?
No, current research does not support this, supplementation only shows benefit in people with an actual documented deficiency.
Who is most at risk for B12 deficiency after 50?
Men taking metformin long-term show notably higher deficiency rates, along with anyone with reduced stomach acid production that impairs B12 absorption from food.
How is B12 deficiency diagnosed?
Through blood testing, not guessing, since normal-range levels can still show subtle effects in some research.
Disclaimer: This article is for informational purposes only and is not intended as medical advice. It does not replace consultation with a licensed healthcare professional. B12 deficiency should be confirmed through blood testing before supplementing, especially if you take metformin or other medications affecting absorption. Individual results vary, and supplements are not regulated the same way as prescription medications.