Recommended amounts of vitamin B12 vary depending on age, but adults require 2.4 micrograms per day, according to the National Institutes of Health. Pregnant and breastfeeding women need about 2.6 micrograms per day. Vitamin B12 helps maintain nerve and blood cell health in addition to assisting in DNA production.
Vitamin B12 is unavailable in plants and is mostly found in animal products or fortified foods, states the National Institutes of Health. Beef liver and clams are good sources of vitamin B12, as are fish, meat, poultry, eggs and milk. Vitamin B12 deficiency affects between 1.5 and 15 percent of Americans.