Daily Requirements
1 to 3 years 0.9 mcg per day
4 to 8 years 1.2 mcg per day
9 to 13 years 1.8 mg per day
14+ years 2.4 mg per day
Vitamin B12 supplements have been recommended for improving cognitive skills and to boost energy. However, research hasn't provided sufficient evidence for these recommendations. Vitamin B12 supplements will reduce homocysteine levels in your blood, though supplementation does not appear to reduce the risk of cardiovascular disease.
Vitamin B12 is found naturally in meats, poultry, seafood, eggs, and dairy products. Supplementation should not be necessary for healthy adults, except for vegans, as vitamin B12 is only found in animal products. People with medical disorders such as pernicious anemia, celiac disease, atrophic gastritis or Crohn's disease may require supplemental vitamin B12 (often taken as shots).
Sources:
"Vitamin B12." Accessed March 17, 2009. http://ods.od.nih.gov/factsheets/vitaminb12/.
Otten JJ, Hellwig JP, Meyers LD. "Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." IOM, 2006.

