It's been a little while since I last posted a Science Byte - seems I just kept putting it off, not too sure what to write. But lately I've been wondering about vitamin B12 & why some people need to get a B12 shot... so why not look into it & tell you guys? I enjoyed the point form style of the last Science Byte, so that's how I'll do this one too.
I found the following information in Robbins & Cotran's Pathologic Basis of Disease.
- vitamin B12 is also known as cobalamin
- humans are totally dependent on dietary B12 - we need about 2 - 3 mg (micrograms)
- in the food chain, B12 is produced mainly by microorganisms - that means plants & vegetables have virtually no B12. A strict vegetarian diet does not provide enough B12.
- eating meat, fish & dairy provides a sufficient amount of B12 - enough to store a couple of years worth of the vitamin in the liver.
- B12 is a cofactor for 2 important reactions. The first reaction is catalyzed by the enzyme methionine synthase - basically, this enzyme forms methionine (an essential amino acid - without it, you can't start protein synthesis) from homocysteine (a fairly toxic compound if it accumulates) but only if B12 is present. At the same time, folate is transformed into a form that will act as a cofactor for another important reaction (this one forms dTMP, a precursor of DNA - without folate, DNA synthesis is compromised). The second reaction is even more complicated (if you can imagine), but essentially without B12 a compound accumulates... & somehow this leads to neurological complications. It may be that abnormal lipids are incorporated into neuronal lipids, leading to their breakdown. Neuronal lipids form the myelin sheath - an insulator for neurons, allowing the electrical impulses to travel faster & further.
- pernicious anemia is believed to be caused by an auto-immune attack on the intestinal cells, disrupting B12 absorption & leading to B12 deficiency. Deficiency can also result from some medications interfering with B12 absorption. Common symptoms are fatigue, irritability, depression, weakened concentration & memory loss. However, symptoms often don't develop before the anemia is quite severe. High-dose vitamin B12 pills or a B12 shot are the necessary treatment.