Wednesday, June 24, 2015
Wisdom Wednesday: Vitamers
No, that’s not a misprint or spelling error although spell check doesn’t recognize vitamers. A vitamer of a particular vitamin is any of a number of chemical compounds, generally having a similar molecular structure. All vitamers show vitamin-activity in vitamin-deficiency biological systems, but not necessarily in humans.
Some of these vitamers are familiar to you. For example, Vitamin A has at least six vitamer chemicals that all qualify as “vitamin A”. In the vitamin A family, four of the chemicals naturally found in foods are carotenoids (alpha-carotene, beta-carotene, gamma-carotene and xanthophylls). These chemicals give fruits and vegetables the colors of red, yellow, and orange. Retinols, and retinal forms, found in animal-based foods, are however many times more active in the human body.
Typically, the vitamin activity of multiple vitamers is limited by the body’s ability to convert one vitamer to another, or to add the enzymatic cofactor(s) to make the bioavailable or bio-active form of the vitamin.
Vitamin B12 occurs in foods as cyanocobalamin. When it is absorbed into the epithelial lining of the small intestine, the epithelial cells convert cyanocobalamin to one of two biologically active forms – methylcobalamin or adenosylcobalamin. The cyanide is stripped off of cobalamin and a methyl group or adenosyl group (the enzymatic cofactors) are substituted. The active vitamer is then released into the blood stream to function as vitamin B12.
Methylcobalamin is used to facilitate over 200 different chemical pathways in the body, including the manufacture of red blood cells. So a deficiency of methylcobalamin results in anemia. Unfortunately, injections of cyanocobalamin are frequently prescribed for anemia and are ineffective because it is not a biologically active form in the human body. It must pass through the wall of the small intestine (taken orally or in food form) to be converted.
Adenosylcobalamin is the form of vitamin B12 needed for athletic activity. I often find this vitamer is needed in triathletes or marathon runners. However, the patient that just can’t seem to walk up a flight of stairs without severe fatigue may also be deficient in adenosylcobalamin.
Vitamin D has five vitamers. Calcitriol, ergocalciferol (D2), and cholecalciferol (D3) are all found in food. However, none of these forms has biological activity in the human body. Vitamin D3 is converted to 25-hydroxy vitamin D in the liver then released into the blood stream. Although stable, it is not biologically active either. The kidneys then covert 25-hydroxy vitamin D to 1,25-hydroxy vitamin D, the active vitamer in the human body. Every cell in the body can also make this final conversion for use in the individual cells.
Humans can also manufacture vitamin D3 from cholesterol in the skin when exposed to sunlight. However, vitamin D deficiency has become all too common as we limit sun exposure in an effort to reduce the frequency of skin cancers. The ironic twist is that vitamin D appears to be vital to the immune system in preventing many forms of cancer.
The chemistry of vitamins/vitamers is quite complex. Scientists have unraveled a lot of information but we still have a lot to learn about the chemistry of the human body in health and disease. Make sure you are working with a knowledgeable professional when consulting on nutrition.