Your small intestine is the longest part of your digestive tract, where vitamin B-12 and all other nutrients are absorbed. It has three parts: the duodenum, the jejunum and the ileum. B-12 absorption takes place in the last section of your small intestine, the ileum. Your bloodstream can absorb B-12 only after it goes through certain digestive phases.
Small Intestine
Your small intestine is 20 feet long. It plays an important role in digestion. It serves as a portal to your bloodstream for nutrients. The duodenum, which is the first section, receives a thick mixture of partly digested food from the stomach. It breaks nutrients into smaller molecules and sends them off for absorption. The jejunum and ileum -- the second and third sections -- contain villi, which are finger-like protrusions. This is where vitamins, minerals and other nutrients are absorbed.
B-12
Vitamin B-12 is a large, complex molecule bound to protein. It plays a crucial role in red blood-cell formation. It also helps synthesize genetic material, known as DNA and RNA. Red blood cells transport oxygen-rich blood and nutrients throughout your body. B-12 deficiency can cause anemia, which is a low red blood-cell count. Anemia reduces your oxygen capacity and prevents your organs and tissues from receiving enough oxygen.
B-12 Absorption
You get B-12 from protein-rich animal foods. Your stomach acid and the pancreatic enzyme pepsin break B-12 into a smaller molecule. They separate B-12 from its protein. Intrinsic factor, a protein needed for B-12 absorption attaches itself. B-12 then travels to the small intestine. The terminal ileum, which is the bottom of your intestine where it meets the large intestine, absorbs B-12 into your bloodstream. Your intestines absorb no B-12 without intrinsic factor.
Aborption Factors
Inadequate stomach acid impairs B-12 absorption, because this is the first digestive phase. Inadequate intrinsic-factor production impairs B-12 absorption, as well. Stomach surgery, such as gastric bypass, can impair your ability to make intrinsic factor. Gastric-bypass patients commonly require B-12 injections after surgery. Your immune system attacks intrinsic factor if you have pernicious anemia. This abnormal immune response can prevent B-12 absorption.
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