Animal products (meat and dairy products) provide the onlydietary source of vitamin B12 for humans. Since B12 is only found in animal sources, vegans and vegetarians are sometimes deficient in B12. The elderly are also more likely to suffer from B12 deficiencies due to multiple steps involved in B12 absorption. People who have a difficult time absorbing B12 may suffer from a condition called pernicious anemia. The usual western diet contains 5 to 7 micrograms of vitamin B12 per day, while the minimum daily requirement is listed as 6 to 9 micrograms per day. Approximately one-half of the total body store is in the liver.
Dietary B12 in the presence of acid and pepsin in the stomach is released from the food and then quickly binds to R factors in saliva and gastric juice. Vitamin B12 bound to R factors is not absorbed. Absorption occurs in the alkaline environment of the duodenum. In this alkaline environment, vitamin B12 is freed from R proteins by pancreatic proteases and then binds specifically and rapidly to gastric-derived intrinsic factor. Intrinsic factor has very high affinity for vitamin B12. The intrinsic factor-vitamin B12 complex binds to specific intestinal receptors and it is absorbed in an energy requiring process that is still incompletely understood.
Thus, adequate absorption of vitamin B12 depends upon five factors.
- · Dietary intake (aim for healthy meat such as fish or chicken or choose egg or dairy items)
- Proper acid-pepsin in the stomach to release B12 from binding to food particles.
- Pancreatic proteases to free B12 from binding to R factors
- Secretion of intrinsic factor by the gastric parietal cells in the stomach to bind to B12
- An ileum (specific section of the small intestine) with vitamin B12-intrinsic factor receptors.
Once taken up by the specific intestinal cells, the vitamin B12 travels along the blood stream by binding to transcobalamin II. This complex binds to specific cell surface receptors in order to enter the cell. Vitamin B12 in the cells is metabolized into two coenzymes: adenosyl-cobalamin; and methyl-cobalamin. It is crucial that every single step along the way is working adequately in order for vitamin B12 to be absorbed properly.
Finally, other medications can interfere with vitamin B12 absorption. The University of Maryland Medical Center claims that some medications used to control diabetes and cholesterol, as well as chemotherapy medications, antibiotics and anticonvulsants, can reduce your ability to absorb vitamin B12.
For more information about vitamin B12 supplementation or injections, please contact Dr. Lee via email firstname.lastname@example.org or 206-319-5322. Don’t forget to ask about B12 happy hour where B12 injections are only $12.