The recommended dietary allowance of vitamin B-12 for adults is 2.4 micrograms per day, reports MedlinePlus. Pregnant women should increase their vitamin B-12 intake to 2.6 micrograms per day, and women should increase their intake to 2.8 micrograms per day when breastfeeding, says WebMD.
Vitamin B-12 plays a role in the body's synthesis of DNA. It is found in many foods, including meat, fish, eggs and dairy products, and it can also be manufactured in a lab, according to Mayo Clinic. Supplementation of vitamin B-12 is used in a variety of conditions including heart disease, Alzheimers disease, memory loss, depression, asthma, AIDs, allergies and diabetes, says MedlinePlus.