FUNCTIONS:
Iron is one of the most abundant metals in the universe. It is also one of the most useful in biochemical functions. In the human body, iron is present in all cells and has several vital functions -- as a carrier of oxygen to the tissues from the lungs in the form of hemoglobin (Hb), as a facilitator of oxygen use and storage in the muscles as myoglobin, as a transport medium for electrons within the cells in the form of cytochromes, and as an integral part of enzyme reactions in various tissues. Too little iron can interfere with these vital functions and lead to morbidity and mortality.
Low iron levels in the blood are the most common and most prevalent mineral deficiency. Iron deficiency can be a very difficult diagnosis, since the symptoms such as lethargy, tiredness and dizziness, are non-specific can be found in a variety of ailments. However, people who are most at risk, including menstruating and pregnant women, athletes, and vegetarians may have difficulty getting adequate iron supplies from their food sources alone.
As co-enzymes, the B vitamins are essential components in most major metabolic reactions. They play an important role in energy production, including the metabolism of lipids, carbohydrates, and proteins. B vitamins are also important for blood cells, hormones, and nervous system function. As water-soluble substances, B vitamins are not generally stored in the body in any appreciable amounts (with the exception of vitamin B-12). Therefore, the body needs an adequate supply of B vitamins on a daily basis.
Thiamin, riboflavin, and niacin are all essential coenzymes in energy production. Thiamin is converted quickly into thiamin pyrophosphate, which is required for glycolytic and Krebs cycle reactions. Thiamin also appears to be related to nerve impulse transmission. Riboflavin is a component of the coenzymes FAD and FMN, which are intermediates in many redox reactions, including energy production and cellular respiration reactions. Niacin is also a component of the coenzymes NAD and NADP, which are involved in energy production, as well as biosynthetic processes.
Vitamin B-6 is a coenzyme in amino acid metabolism. It is necessary for the metabolism of homocysteine and the conversion of tryptophan into niacin. Vitamin B-6 dependent enzymes are also needed for the biosynthesis of many neurotransmitters, including serotonin, epinephrine, and norepinephrine. Vitamin B-12 and folic acid are coenzymes in DNA and RNA metabolism. Both of these B vitamins assist in homocysteine metabolism. Folic acid serves as a methyl donor and vitamin B-12 as a coenzyme in the conversion of homocysteine to methionine.
Pantothenic acid is a coenzyme essential for energy production from dietary fats, carbohydrates, and proteins. Pantothenic acid is a component of coenzyme A and of phosphopantetheine, and is therefore essential for Krebs cycle operation.
Vitamin E is an especially valuable antioxidant in the cell membranes, where it prevents oxidation of unsaturated fatty acids by trapping free radicals. This helps stabilize and protect cell membranes, especially red blood cells and tissues sensitive to oxidation, such as the lungs, eyes, and arteries.
While not truly a vitamin, choline is an important nutrient related to B vitamins. Choline serves as a methyl donor for homocysteine metabolism following conversion to betaine, as a structural component of cellular membranes as phosphatidylcholine, and as a neurotransmitter as acetylcholine.
REFERENCES:
1. Hallberg L: Bioavailability of dietary iron in man. Ann Rev Nutr 1981;1:123-147.
2. Hallberg L, Rossander-Hulten L: Iron requirements in menstruating women. Am J Clin Nutr 1991;54:1047-1058.
3. Jansonius, JN. Structure, evolution and action of vitamin B6-dependent enzymes. Curr Opin Struct Biol 1998;8:759-69.
4. Lakshmi, AV. Riboflavin metabolism--relevance to human nutrition. Indian J Med Res 1998;108:182-90.
5. Nilsson-Ehle, H. Age-related changes in cobalamin (vitamin B12) handling. Implications for therapy. Drugs Aging 1998;12:277-92.
6. Scott, JM, Weir, DG. Folic acid, homocysteine and one-carbon metabolism: a review of the essential biochemistry. J Cardiovasc Risk 1998;5:223-7.
7. Tahiliani, AG, Beinlich, CJ. Pantothenic acid in health and disease. Vitam Horm 1991;46:165-228.
8. Zeisel, SH. Choline. A nutrient that is involved in the regulation of cell proliferation, cell death, and cell transformation. Adv Exp Med Biol 1996;399:131-41.
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