Vitamin B-12 is classified as one of the water-soluble essential organic compounds. This means that humans need it to survive but cannot produce it on their own. Vitamin B-12 plays a vital role in oxygen transport by supporting the production of healthy red blood cells. The body also needs vitamin B-12 for neurological function and the production of genetic material known as DNA. To avoid disease caused by a deficiency, meet the daily recommended intake provided by the National Institute of Medicine's Food and Nutrition Board.
Daily Recommended Intake
The amount of vitamin B-12 you need depends on your age and special circumstances. Infants between the ages of 0 and 6 months need 0.4 mcg per day while those between 7 and 12 months need 0.5 mcg per day. As children get older they need more red blood cells which require more B-12. Children ages 1 to 3 need 0.9 mcg per day and those ages 4 to 8 need 1.2 mcg per day. Boys and girls between the ages of 9 and 13 need 1.8 mcg per day while adolescents and adults older than the age of 14 need 2.4 mcg per day. Pregnant women experience a 40 to 50 percent increase in blood volume and a 33 percent increase in red blood cells to accommodate the circulation to the developing baby. To support this pregnant women require more vitamin B-12, up to 2.6 mcg per day and lactating women need 2.8 mcg per day.
Deficiency
Although vitamin B-12 is classified as a water-soluble vitamin, which means it dissolves in water and the body can excrete excess in the urine, the body can actually store several years worth, according to MayoClinic.com. Even so, chronically failing to intake the recommended daily amount or suffering from a disease that interferes with the absorption of vitamin B-12 can lead to a deficiency. A vitamin B-12 deficiency causes megaloblastic anemia, a condition characterized by large hemoglobin-poor red blood cells that cannot carry oxygen. Symptoms include fatigue, dizziness, numbness and tingling in the hands and feet, difficulty walking and memory loss.
Sources
Bacteria produce vitamin B-12 meaning only animal products --- including meat, poultry, fish and milk --- contain vitamin B-12. For example, 3 oz. of steamed clams contains 84 mcg of B-12, 3 oz. of baked salmon contains 2.4 mcg --- the recommended daily intake --- and 8 oz. of skim milk contains 0.9 mcg. Vegetarians who consume no animal products must take vitamin B-12 supplements to meet their daily needs.
Tolerable Upper Intake Level
The level of vitamin B-12 found in food sources is so low that consumption of too much remains rare. Even when taking vitamin B-12 supplements researchers fail to find any adverse effects from vitamin B-12. This could be due to the fact that the body only absorbs a fraction of the total vitamin available in high dose supplements. Because of this, the National Institute of Medicine has not set a tolerable upper intake level --- the amount of the vitamin most likely to cause adverse health effects for the average adult.
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