Requirements: Vitamin B12 is essential but required only in minute amounts; 3-4 mcg. is needed in most adults to prevent deficiency, and at least that amount is required by pregnant or lactating women, as well as infants and growing children. From 10-20 mcg. daily is a good insurance level, although certain people may need increased amounts with higher protein intake. Vitamin B12 is often taken in higher doses, 500-1000 mcgs. per day, to relieve fatigue. Injections of B12 in these amounts are used to treat a variety of low-energy and mental symptoms previously described as well as during some weight loss programs. When there is fatigue or anemia, it is a good idea to get the blood level of B12 checked by a doctor. It may lead to a very simple and successful treatment.