What does Vitamin B12 do?

Vitamin B12 is needed for normal nerve cell activity, DNA replication, and production of the mood-affecting substance called SAMe (S-adenosyl-L-methionine). Vitamin B12 works with folic acid to control homocysteine levels. An excess of homocysteine, which is an amino acid (protein building block), may increase the risk of heart disease, stroke, and perhaps osteoporosis and Alzheimer’s disease.

Vitamin B12 deficiency can cause fatigue, and some research indicates that individuals who are not deficient in this vitamin have increased energy after injections of vitamin B12. In one unblinded trial, 2,500–5,000 mcg of vitamin B12, given by injection every two to three days, led to improvement in 50–80% of a group of people with chronic fatigue syndrome (CFS), with most improvement appearing after several weeks of B12 shots. While the research in this area remains preliminary, people with CFS interested in considering a trial of vitamin B12 injections should consult a nutritionally oriented doctor. Oral or sublingual B12 supplements are unlikely to obtain the same results as injectable B12, because the body’s ability to absorb large amounts is relatively poor.

Where is Vitamin B12 found?

Vitamin B12 is found in all foods of animal origin, including dairy, eggs, meat, fish, and poultry. Inconsistent but small amounts occur in seaweed (including spirulina) and tempeh.
Who is likely to be Vitamin B12 deficient?
Vegans (vegetarians who also avoid dairy and eggs) frequently become deficient, though the process may take many years. People with malabsorption conditions may suffer from vitamin B12 deficiency. Individuals suffering from pernicious anemia require high-dose supplements of vitamin B12. Older people with urinary incontinence3 and hearing loss have been reported to be at increased risk of B12 deficiency.

How much Vitamin B12 is usually taken?

Most people do not require vitamin B12 supplements. However, vegans should take at least 2–3 mcg per day. Treatment for pernicious anemia includes supplements of 1,000 mcg of vitamin B12 per day or vitamin B12 injections. Despite the beliefs of many medical doctors, scientific proof indicates that oral supplementation (1,000 mg per day) provides successful therapy and that vitamin B12 injections are not needed. In addition, the elderly may benefit from 10–25 mcg per day of vitamin B12.