Vitamin B-12 is essential for metabolism, forming DNA and red blood cells, central nervous system function, and immune system function. Most people who eat meat get plenty of vitamin B-12 from their diet, but elderly people, vegetarians and people who have gastrointestinal disorders may have more difficulty getting enough vitamin B-12 through their diets.
Requirements for vitamin B-12 depend on your age. Infants up to 6 months old need 0.4 micrograms per day and those between 7 and 12 months of age need 0.5 micrograms per day. The recommended dietary allowance for children between the ages of 1 and 3 is 0.9 micrograms, children between the 4 and 8 need 1.2 micrograms and children between 9 and 14 need 1.8 micrograms per day. People aged 14 and over need 2.4 micrograms, except for pregnant women, who need 2.6 micrograms, and breastfeeding women, who need 2.8 micrograms per day. These are the minimum requirements. The daily value for this vitamin is 6 micrograms per day.
The only reliable food sources for vitamin B-12 are animal-based foods, including meat, seafood, poultry, eggs and dairy. A 3-ounce serving of cooked clams contains 84.1 micrograms of vitamin B-12, or 1,402 percent of the daily value; a 3-ounce serving of cooked rainbow trout contains 5.4 micrograms, or 90 percent; a double cheeseburger contains 2.1 micrograms, or 35 percent; 1 cup of low-fat milk contains 1.2 micrograms, or 18 percent; and a hard-boiled egg contains 0.6 micrograms, or 10 percent.
Absorption of vitamin B-12 requires both a substance called intrinsic factor and hydrochloric acid. People with ulcers or a genetic condition called pernicious anemia may not make enough intrinsic factor to absorb adequate amounts of vitamin B-12. Older individuals, people who have digestive disorders and people who have had gastrointestinal surgery also have difficulties absorbing this vitamin because their bodies may not make sufficient amounts of hydrochloric acid, which is needed to free the vitamin B-12 from the protein in food. The vitamin B-12 in supplements and fortified foods is in a different form, which doesn't require hydrochloric acid for absorption, so these sources are recommended for people older than 50 and for those with absorption issues.
Strict vegetarians and vegans usually need to take a supplement to get an adequate amount of vitamin B-12, unless they consume enough foods that are fortified with this nutrient. Some breakfast cereals are fortified with 100 percent of the daily value for vitamin B-12, and some milk replacements are fortified as well.
- CLAMS image by brelsbil from Fotolia.com