Overview
Vitamins are organic essential nutrients required in small amounts by the body. So far, 13 vitamins have been identified. Some dissolve in water and can be stored by the body for only a few weeks. Others dissolve in fat and can be stored in fat tissue for months or years. Vitamins must be intact to work properly. These complex molecules can be damaged by heat, light and chemicals. To preserve vitamins in vegetables, avoid high temperatures and long cooking times.
Function
Although vitamins do not produce energy on their own, they do assist in the release of energy from the carbohydrates, fats, and proteins in foods. Likewise, vitamins do not serve as structural components, but they do help collagen do that work. Nearly all chemical reactions in the body need the assistance of vitamins. For example, some are coenzymes that activate an enzyme that increases the rate of chemical reactions in metabolism. One helps the eye to see at night; one helps make hormones. If an injury occurs, one vitamin stops the bleeding and another helps heal the skin. The lining of the digestive tract and red blood cells must be frequently replaced, and vitamins are there to help with these and all other important functions of the body.
For a health smart quick reference guide, see the Texas Heart Institute’s “Vitamins: What They Do and Where to Get Them” article in Resources.
Fat-soluble Vitamins in Food
Vitamins A, D, E, and K are fat soluble. Vitamin A and its precursors in carrots and meat help eyesight, skin and bones. Vitamin D in fortified milk and eggs is needed for calcium and phosphorus metabolism. Vitamin E in oils and whole grains is an antioxidant. Vitamin K in whole grains and green leafy vegetables is also produced by friendly intestinal bacteria and aids in blood clotting.
Water-soluble Vitamins in Food
The B complex vitamins and vitamin C are water-soluble. Vitamin B1, also called thiamin, helps metabolize carbohydrates. Vitamin B2 or riboflavin helps tissue growth and repair. Vitamin B3 or niacin and pantothenic acid help with energy metabolism. Vitamin B6 or pyridoxine is a coenzyme for metabolism. Folate is needed for DNA and regulates homocystine. Vitamin B12 is needed for DNA and red blood cells. Biotin assists fat and protein metabolism. Vitamin C or ascorbic acidd is an antioxidant. Eating a wide variety of fruits and vegetables, whole grains and protein sources such as meat, beans and nuts will supply all of the B complex vitamins.
Supplemental Vitamins
Vitamin supplements are appropriate in some cases to correct deficiencies or reduce the risk of disease. Supplemental vitamins may also be needed to support increased nutrient needs due to illness, injury or surgery and to support the immune system.
Recommended Intake
Vitamin deficiencies produce specific disease symptoms and excess levels from high supplement dosages can produce toxicity. The Dietary Reference Intakes include the Recommended Dietary Allowance, which is the amount that is adequate to meet the needs of most healthy people; Adequate Intake or AI, the average amount healthy people typically consume; and Tolerable Upper Limit or UL, the maximum amount that appears safe for most healthy people. The Dietary Reference Intakes are established by the Food and Nutrition Board of the Institute of Medicine in cooperation with scientists in Canada.
On a food label, vitamins and minerals are listed in descending order of predominance by weight. Nutrition food labels must also present nutrient content percentage information for vitamins A and C compared to a Daily Value established by the Food and Drug Administration. Unlike the Dietary Reference Intakes, which are individualized based on age, gender and pregnancy or lactation status, Daily Values are meant to represent the needs of a “typical consumer” with a 2,000 calorie intake for the purpose of food labeling. The Dietary Supplement Health and Education Act of 1994 subjects supplements to the same general labeling requirements that apply to foods.
About this Author
Norma DeVault, a registered dietitian, has been writing health-related articles since 2006. Her articles have appeared in the “Journal of the American Dietetic Association.” She holds a Doctor of Philosophy in human environmental sciences from Oklahoma State University and a Master of Business Administration from the University of Tulsa.
