Vitamins are a broad class of biological molecules that share little similarity in their chemistry but are unified by their strict necessity in living systems for normal metabolism. Since vitamins are all necessary for proper function of your body, it is not possible to rank them by "importance"--they are all equally important. Rather, the importance of taking vitamins is ensuring that enough of each is consumed and that any dietary deficiencies are satisfied by supplementation.
Essentiality of Vitamins
Vitamins are often defined as "essential" or "nutritionally essential." Essential nutrients are defined as those which an organism cannot make itself and must be obtained through the diet. Thus, if sufficient levels of a vitamin aren't consumed, the organism's metabolic processes will not have access to this critical molecule and a dysfunction can occur. Most of the vitamins in human nutrition were in fact discovered though the diseases that were caused by their dietary deficiencies. Scurvy, beriberi, and pellagra are three vitamin deficiency diseases which ultimately led to the discovery of vitamins C, B1, and B3, respectively.
Essential vitamins in one organism are not necessarily essential in another. Vitamin K, for example, is an essential nutrient in humans for blood clotting and bone growth, but is nonessential in plants---they can synthesize all the vitamin K that they need for photosynthesis.
Essential Human Vitamins
Essential vitamins in humans are the B complex vitamins and vitamins A, C, E, and K. B complex vitamins include thiamine, riboflavin, niacin/niacinamide, pantothenic acid, pyridoxine and its derivatives, biotin, folic acid, choline, and cobalamin.
B complex vitamins serve as necessary cofactors for metabolic reactions that synthesize and break down amino acids, fats, and carbohydrates, generate cellular energy, construct cell membranes, produce neurotransmitters and hormones, and detoxify potentially harmful chemicals. Vitamin A in the form of retinol is used as a cofactor for rhodopsin, an important light-sensing protein in vision; vitamin A is also used to to control the expression of certain genes, and can act as a fat-soluble antioxidant.
Vitamins C and E are essential antioxidants; vitamin C prevents oxidative damage in the aqueous portions of cells, while vitamin E prevents the oxidation of fats. Vitamin D is not strictly essential in human metabolism; the body can make its own vitamin D by the action of UV light on cholesterol stored in skin cells. It is nonetheless important for the uptake and balance of minerals, like calcium, and the proper function of the kidneys and cardiovascular system.
Should You Be Taking More?
Because so many metabolic reactions in your body require adequate amounts of essential vitamins, it is important to get enough of each in the diet. Those with well-rounded diets are likely getting sufficient levels of most of the essential vitamins. Notable exceptions to this are for choline and vitamin D. According to one analysis of the National Health and Nutrition Education Survey, less than 10 percent of Americans consume the recommended daily intake of choline, and essential nutrient for proper brain development. The further your diet strays from balance, however, the more likely supplementation may be necessary. Vegan diets, for example, can be deficient in vitamin B12, which is predominantly found in animal products.
An Essential Nonessential Vitamin?
Ironically, the nonessential vitamin D is a probably the largest concern for most people in terms of dietary levels. In about half of the United States, there is insufficient UVB irradiation during winter months to produce enough vitamin D, leaving many individuals with suboptimal levels, according to a study published in the "Journal of Nutrition." Despite the fact that most milk products are fortified with vitamin D, only about half of children receive the recommended 200 IU per day, according to one analysis.
Other Essential Nutrients
While many individuals concentrate on adequate vitamin intake, it is important to remember that vitamins are not the only nutritionally essential elements in the diet. Equally important to proper metabolism are sufficient levels of essential trace elements--minerals-- notably calcium, magnesium, potassium, and iron, as well as the nine essential amino acids and the essential fatty acids alpha-linolenic acid and linoleic acid. Each one of these nutrients, like the vitamins, is required for the proper function of one or more metabolic pathways.
References
- "The Journal of Nutrition" Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D", B. W. Hollis, 2005
- "Journal of Nutrition", Vitamin D Intakes by Children and Adults in the United States Differ Among Ethnic Groups. C.E. Moore, M.M. Murphy, M.F. Holick, 2005
- "Nutrition Reviews", Choline: An Essential Nutrient for Public Health, S. H. Zeisel, K.A. da Costa, November, 2009
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