Vitamin B12 belongs to the B vitamin group, which is water soluble. Because the human body cannot make B12, doctors classify it as an essential vitamin. The Dietary Reference Intakes provided by the Food and Nutrition Board lists the daily recommended requirement of vitamin B12 for various age groups.
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The human body requires vitamin B12 to support many functions throughout the body. The production of red blood cells, the cells in the blood responsible for carrying oxygen throughout the body, requires vitamin B12, which also promotes a healthy nervous system as it helps to maintain myelin—the fatty substance that surrounds nerves. Vitamin B12 also triggers the production of substances required to make DNA—the part of each cell that carries genetic information.
Although current research has found a few plant sources of vitamin B12, such as seaweeds and algae, the B12 in those sources is likely to be unavailable for absorption by humans, according to the Vegetarian Society. The only natural sources of vitamin B12 remain animal sources. Meats, such as beef liver, poultry and fish serve as good dietary sources of B12. Dairy products, defined by the U.S. Department of Agriculture as products produced from milk that retain their calcium content, also contribute to the daily requirement of B12. Eggs, another animal product, provide many nutrients, including vitamin B12. In addition to natural sources, manufacturers fortify many foods with vitamin B12, such as breakfast cereals.
Because the human body stores several years’ worth of vitamin B12, according to MayoClinic.com, deficiency rarely occurs, and daily requirements remain low. The daily requirements for vitamin B12 differ for different age groups to account for body size, tied to the number of red blood cells produced daily. Infants age 0 to 6 months require 0.4 mcg, with 1,000 mcg equaling 1 mg. The requirement increases to 0.5 mcg for babies 7 to 12 months of age. Children 1 to 3 years old require 0.9 mcg, while those ages 4 to 8 require 1.2 mcg and ages 9 to 13 require 1.8 mcg, as listed by the National Institutes of Health Office of Dietary Supplements.
Adults, both male and female, require 2.4 mcg of vitamin B12 daily. Becoming pregnant increases the requirement to 2.6 mcg to support the additional volume of blood and the need for red blood cells. In addition, women who are lactating should consume 2.8 mcg per day because vitamin B12 is excreted into milk.
Patients deficient in vitamin B12 may suffer from anemia, due to a decrease in red blood cells, and nerve degeneration due to damage to myelin. Vitamin B12 deficiency, therefore, requires prompt treatment to avoid additional complications. Taking daily oral supplements can help boost vitamin B12 levels. Oral supplements, however, cannot treat deficiencies caused by conditions that interfere with the absorption of nutrients. For these conditions, such as pernicious anemia, doctors prescribe vitamin B12 delivered through intramuscular injections, thereby bypassing the digestive system.