You need B12 to make red blood cells, which carry oxygen through your body. Not having enough B12 can lead to anemia, which means your body does not have enough red blood cells to do the job. This can make you feel weak and tired.

How much B12 should I take daily for anemia?

Left untreated, a vitamin B-12 deficiency can lead to anemia, fatigue, muscle weakness, intestinal problems, nerve damage and mood disturbances. The recommended daily amount of vitamin B-12 for adults is 2.4 micrograms.

How long does it take for B12 to help anemia?

Anemia usually resolves in about 6 weeks. But if severe symptoms due to nerve damage last for months or years, they may become permanent. In most older people with vitamin B12 deficiency and dementia, mental function does not improve after treatment.