Vitamin B12 is a nutrient that is important for many aspects of human health. Adequate levels of vitamin B12 are needed for your body to maintain a healthy nervous system, make red blood cells, and create DNA, the genetic material present in all of our cells.
Vitamin B12 occurs naturally in animal proteins, such as red meat, fish, poultry, eggs, and dairy. Other foods, like breakfast cereals, nutritional yeast, and some plant milks, may be fortified with vitamin B12. This vitamin is also available as a supplement and as a prescription medication.
In food, vitamin B12 is bound to protein. In order for your body to absorb it, the vitamin must be released from the protein. As your body digests food, enzymes in your digestive tract separate vitamin B12 from these proteins. The freed vitamin B12 then combines with a protein made by your body called intrinsic factor, which is secreted by cells in the stomach. Together, vitamin B12 and intrinsic factor are absorbed in the lower end of the small intestine.