NIH Office of Dietary Supplements — Vitamin B12 fact sheet for health professionals

This fact sheet summarizes research on vitamin B12, a nutrient that helps make blood cells, maintain nerve cells, and build DNA, the molecule carrying genetic instructions. Most people can get enough from meat, fish, eggs, dairy foods, or fortified foods, meaning foods with added vitamins. Adults generally need 2.4 micrograms daily, while pregnant or breastfeeding people need slightly more. Deficiency, meaning too little B12, can cause anemia, tiredness, numbness, and nerve problems, especially in older adults, vegans, and people with absorption problems. Supplements help when someone is deficient, but research does not show that extra B12 boosts energy or prevents disease in people who already get enough.

What this means for you: Buy a B12 supplement if a clinician identifies a deficiency or you have a higher-risk diet or medical condition. Extra B12 is unlikely to improve energy or longevity when your levels are already adequate.