What are the symptoms of B12 deficiency?
B12 deficiency causes megaloblastic anemia, with fatigue, weakness, shortness of breath and pale skin. Nerve damage brings tingling or numbness in the hands and feet, balance problems, memory trouble and depression. Neurological damage can become permanent if it goes untreated too long (Green et al., 2017).
Who is most at risk?
B12 needs stomach acid and intrinsic factor to be absorbed, so risk is higher for vegans, adults over 50, people who've had weight-loss or stomach surgery, long-term users of PPIs or H2 blockers, and people taking metformin for diabetes (Aroda et al., 2016). Clams and beef liver are the richest sources; those with absorption problems may need injections or high-dose pills. See also magnesium.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Can you take too much B12?
- There's no established upper limit because excess is excreted, but megadoses don't help if you're not deficient.
- Do B12 shots boost energy?
- Only if you're actually deficient.
Sources reviewed: 2026-10-25
References
- Green, R., et al. (2017). Vitamin B12 deficiency. Nature Reviews Disease Primers, 3, 17040.
- Aroda, V. R., et al. (2016). Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. JCEM, 101(4), 1754–1761.