Vitamins are organic (carbon-based) compounds that are necessary in tiny amounts for the biochemical activities that take place in our body. Since vitamins cannot be synthesized in our body (except for a few), we take them in with our food. Vitamin B12 (cobalamin) is a complex ringed structure with a cobalt ion in its center. The All-Merciful God gave the duty of synthesizing this vitamin that our body needs to the microorganisms found in the large intestine. Nevertheless, these microorganisms cannot produce the vitamin in sufficient amounts for our body, thus a certain portion of B12 has to be taken in with food. Methods of supplying this vitamin are limited, for it is not synthesized by plants directly either. The best way to obtain this vitamin is to eat liver and kidney, as it is in these organs that the vitamin is stored. It is also found in large quantities in dairy products, fish, and eggs.
It is worth contemplating that humans are in need of microorganisms to survive and that living things as insignificant (!) as bacteria are necessary to synthesize B12 vitamin. Why our so-called bacteria ancestors (!) from which we evolved – as some claim – lost this ability to synthesize B12 vitamin which was, and still is, vital for survival, is a challenging question for those scientists who support the theory of evolution.
The journey of B12 in our body
Cobalamin, which is taken in with food, is absorbed by the final section (ileum) of the small intestine and transported into the blood by receptors on the cell membrane. For B12 to be absorbed into the blood, it is necessary to have an “intrinsic factor” bound to this vitamin. The intrinsic factor is a glycoprotein produced in parietal cells that secrete gastric acid. After the absorption, the vitamin binds to transcobalamin, a carrier protein found in the blood, and it is then being bound with transcobalamin II so that it can penetrate the cells. B12 can be stored in the liver to meet the needs of our body for a long time. A deficiency in cobalamin due to a poor diet (e.g., vegetarians) or a failure to produce the intrinsic factor in the stomach may result in pernicious anemia, which is fatal. Cobalamin deficiency negatively affects DNA synthesis, which is necessary for production of new cells, particularly in the division of the stem cells that are assigned to construct new red blood cells. This is followed by the circulation of cells that will generate underdeveloped red blood cells; these cells will not be able to function properly and will have larger diameters.
The training of parietal cells
If the stomach is removed or cannot produce the intrinsic factor, it is impossible for B12 to be absorbed. It is worth reflecting on the wisdom of why an organ like the stomach, the main duty of which is to partially digest food and convey it to the intestines, synthesizes intrinsic factor. How can the stomach know that our body is in need of this protein? How did it become able to synthesize this very special composition of glucose and protein which is so necessary to absorb intrinsic factor through the gastrointestinal tract? Why doesn’t our body produce the vitamin in the first place, instead of binding it to such a complex molecule? And how do the parietal cells know what is necessary to bind this vitamin, the use of which they cannot understand, although they have never been trained in bio-chemistry, physiology, or pharmacology? In which laboratory did these cells synthesize and test this compound?
The intrinsic factor
In order to decompose proteins into amino acids, the stomach secretes hydrochloric acid and an enzyme called pepsinogen. Parietal cells that secrete acid also produce a protein (intrinsic factor) which is not damaged by the acid or the pepsinogen enzyme. How were these cells able to develop a synthesis in which proteins do not decompose, which can protect them from the acid in the stomach, and bind themselves to a vitamin like B12, which is absorbed only in very small quantities?
The hydrochloric acid secreted in the stomach is like bleach and it irritates anywhere that it goes other than the stomach. Should even the slightest quantity of this acid pass into esophagus (reflux, diaphragm boiling) it can cause severe burning. It is amazing that B12 is found and bound in a cauldron like the stomach, but is not damaged by the acid produced when the stomach is filled with food and drink.
The intrinsic factor bound with the vitamin goes on its journey and it reaches the absorption region in the last section of the small intestines. During absorption, the gates on the cell membrane of the intestines open up only to allow the B12 intrinsic factor compound. Maintained in the intestinal cell for a while, the B12 vitamin binds to the transporter transcobalamin and is conveyed to the cells through the blood. After reaching a cell, the vitamin, needed by the entire body, is bound to another transporter: transcobalamin II.
Some components, although they appear to be very simple, must be supplied from outside our bodies if we are to survive. B12 vitamin is one such component, and it certainly deserves to be studied well.