Table of Contents


Vitamins are organic compounds found in plants and animals that are necessary in small quantities for life and health. Thirteen different vitamins have been identified as necessary for humans. The body can make small quantities of two of these vitamins, vitamins D and K. All other vitamins must be obtained either from food or from dietary supplements.


Each of the 13 vitamins has specific functions, and taken together vitamins play a role in almost every function in the body. They help convert food to energy, and are involved processes as diverse as blood clotting, vision, reproduction, and transmission of nerve impulses.

Essential Vitamins

VitaminWhat it does for the body
Vitamin A (Beta Carotene)Promotes growth and repair of body tissues: reduces susceptibility to infections; aids in bone and teeth formation; maintains smooth skin
Vitamin B-1 (Thiamin)Promotes growth and muscle tone; aids in the proper functioning of the muscles, heart, and nervous system; assists in digestion of carbohydrates
Vitamin B-2 (Riboflavin)Maintains good vision and healthy skin, hair, and nails; assists in formation of antibodies and red blood cells; aids in carbohydrate, fat, and protein metabolism
Vitamin B-3 (niacinamide)Reduces cholesterol levels in the blood; maintains healthy skin, tongue, and digestive system; improves blood circulation; increases energy
Vitamin B-5Fortifies white blood cells; helps the body's resistance to strees; builds cells
Vitamin B-6 (Pyridoxine)Aids in the synthesis and breadown of amino acids and the metabilism of fats and carbohydrates; Supports the central nervous system; maintains healthy skin
Vitamin B-12 (Cobalamin)Promotes growth in children; prevents anemia by regenerating red blood cells; aids in the metabolism of carbohydrates, fats and proteins; maintains healthy nervous system
BiotinAids in the metabolism of proteins and fats; promotes healthy skin
CholineHelps the liver eliminate toxins
Folic Acid (Folate, Folacin)Promotes the growth and reproduction of body cells; aids in the formation of red blood cells and bone marrow
Vitamin C (Ascorbic Acid)One of the major antioxidants; essential for healthy teeth, gums, and bones; helps to heal wounds, fracures, and scar tissue; builds resistance to infections; assists in the prevention and treatment of the common cold; prevents scurvy
Vitamin DImproves the absorption of calcium and phosphorous (essential in the formation of healthy bones and teeth) maintains nervous system
Vitamin EA major antioxidant; supplies oxygen to blood; provides nourishment to cells; prevents blood clots; slows cellular aging
Vitamin K(Menadione) Prevents internal bleeding; reduces heavy menstural flow

Water-soluble vitamins

Humans need nine water-soluble vitamins. These vitamins dissolve in water and are not stored in the body for long periods. Most excess water-soluble vitamins are removed by the kidneys and leave the body in urine. Below is a list of the water-soluble vitamins and a very brief description of their importance to health. For details on how these vitamins function, see the specific entries for each vitamin. In general, B vitamins tend to be involved in reactions that convert nutrients to energy and reactions that synthesize new molecules. There are gaps in the numbering of the B-complex vitamins, because compounds originally named as vitamins, such as B4 (adenine), were renamed after further research showed that theydid not meet the definition of a vitamin.

  • Vitamin B1 (thiamin): needed to convert carbohydrates to energy
  • Vitamin B2 (riboflavin): helps breakdown proteins, fats, and carbohydrates and make other vitamins and minerals available to the body
  • Vitamin B3 (niacin): helps the body process fats and proteins
  • Vitamin B5 (pantothenic acid): helps regulate the chemical reactions that produce energy
  • Vitamin B6 (pyridoxine): involved in the transmission of nerve impulses, formation and functioning of red blood cells, and creation of new cells
  • Vitamin B12 (cobalamin): necessary for healthy red blood cells, creating new deoxyribose nucleic acid (DNA), and in maintaining nerve cells
  • Vitamin C (ascorbic acid): helps form cartilage and connective tissue; as an antioxidant protects cells from free radical damage
  • Vitamin H (biotin): joins with enzymes that regulate the breakdown of foods and their use in the body
  • Folic acid (folate): helps make new cells; important in development of the fetal nervous system

Fat-soluble vitamins

Humans need four fat-soluble vitamins. Unlike water-soluble vitamins, fat-soluble vitamins can be stored in the body. High levels of these vitamins can cause health problems. Below is a list of the water-soluble vitamins and a very brief description of their importance to health. In general the fat-soluble vitamins


B-complex vitamins—A group of water-soluble vitamins that often work together in the body. These include thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7 or vitamin H), folate/folic acid (B9), and cobalamin (B12).

Dietary supplement—A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.

Free radical—A molecule with an unpaired electron that has a strong tendency to react with other molecules in DNA (genetic material), proteins, and lipids (fats), resulting in damage to cells. Free radicals are neutralized by antioxidants.

Functional Food—Also called nutraceuticals, these products are marketed as having health benefits or disease-preventing qualities beyond their basic supply of energy and nutrients. Often these health benefits come in the form of added herbs, minerals, vitamins, etc.

Mineral—An inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples include zinc, copper, iron.

have antioxidant activity that helps protect cells from damage. For details on how these vitamins function, see the specific entries for each vitamin.

  • Vitamin A (retinol): needed for vision, a healthy immune system, development of the fetus, tissue repair; as an antioxidant protects cells from free radical damage
  • Vitamin D (calciferol): involved in building bones, muscle contraction, and nerve impulse transmission.
  • Vitamin E: (tocopherol) acts as an antioxidant to protect the body against damage caused by free radicals
  • Vitamin K: needed for blood clotting

vitamin supplements

Vitamin supplements come as tablets, capsules, and elixirs (liquids). Supplements can contain a single vitamin, a group of related vitamins that work together in the body (e.g. B-complex vitamins), or a mixture of vitamins and minerals (e.g. vitamin D and calcium that work together to build bones). Vitamins are also added to foods that can then be labeled“fortified” or“enriched.” Many so-called functional foods, or nutra-ceuticals, have added vitamins, minerals, and herbs.

In the United States, the Food and Drug Administration (FDA) regulates dietary supplements under the 1994 Dietary Supplement Health and Education Act (DSHEA). Under DSHEA, supplements are subject to the same regulation as food, which is much less rigorous than the regulation of prescription or over-the-counter drugs. Vitamin manufacturers do not have to prove that their products are safe or effective before they can be sold to the public. By contrast, manufacturers of conventional prescription and over-the-counter drugs must prove both safety and effectiveness in extensive humans before their product can be marketed.

In 2007, ConsumerLab, an independent testing company in New York, evaluated 21 brands of multivitamins. They found that only 10 of these multivitamins contained all the vitamins and minerals in the quantities listed on the label. In addition, some brands contained contaminants, including lead. To get the most out of vitamin supplements, consumers should

  • read the label carefully to understand exactly what is in the supplement
  • avoid megadoses of vitamins. The daily value (DV) given on the label should be around 100% for each vitamin.
  • Look for“USP' on the label. This means that the supplement meets the strength and purity standards of the U.S. Pharmacopeia, a testing organization.
  • check the expiration date . stick with well-known brands

Vitamin requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for most vitamins and minerals. The DRIs consist of three sets of values. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97-98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

Experts agree that vitamin supplements are not a substitute for nutrients from food. Most healthy people in developed countries who eat a varied diet high in fruits, vegetables, and whole grains get enough vitamins and do not need a vitamin supplement, although many take a daily multivitamin as“insurance.” However, some groups do tend to need either general supplementation with a multivitamin or supplementation with specific vitamins to prevent vitamin deficiency diseases. People in these groups should discuss their vitamin requirements with their healthcare provider. They include:

  • the elderly, especially those on restricted diets
  • vegans, because they eat no animal products
  • breastfed babies of vegan mothers
  • people with lactose intolerance or those who do not eat dairy products
  • people with alcoholism
  • people who have had part of their stomachs or intestines surgically removed
  • pregnant women or those who could become pregnant
  • people with diseases that interfere with vitamin metabolism
  • people taking drugs that interfere with vitamin metabolism

Vitamin excess


Both too little and too much of any of the 13 human vitamins may cause health consequences. See entries on specific vitamins for more detailed information about potential health concerns.


The interactions among various vitamins, enzymes, coenzymes, drugs, and herbal supplements are complex and incompletely understood. See entries on specific vitamins for more detailed information about their interactions.


Vitamins acquired by eating fruits and vegetables promote health. No complications are expected from vitamins in food. Vitamin supplements may cause hypervitaminosis or interact with other supplements, prescription drugs, over-the-counter drugs, and herbal supplements in ways that cause undesirable side effects. See entries on specific vitamins for more detailed information about potential complications.

Parental concerns

Parents should encourage their children to eat a healthy and varied diet high in fruits, vegetables, and whole grains to meet their vitamin needs.

Most vitamin poisonings and deaths occur in children under age 6 as the result of accidental intake of excessive vitamin supplements. Parents should treat vitamin supplements as they would any drug and store them out of the reach of children.


Gaby, Alan R., ed. A-Z Guide to Drug-Herb-Vitamin Interactions Revised and Expanded 2nd Edition: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. New York: Three Rivers Press, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.


Guyton JR, Bays HE.“Safety considerations with niacin therapy.” Am J Cardiol. (March 19, 2007):S22-31.

Kushi, Lawrence H., Tim Byers, Colleen Doyle, et al.“American Cancer Society Guidelines on Nutrition and Physical Activity for Cancer Prevention.” CA: Cancer Journal for Clinicians., 56 (2006):254-281. <>


American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995. Telephone: (800) 877-1600. Website: <>

Linus Pauling Institute. Oregon State University, 571 Weniger hall, Corvallis, OR 97331-6512. Telephone: (541) 717-5075. Fax: (541) 737-5077. Website: <>

Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892-7517 Telephone: (301)435-2920. Fax: (301)480-1845. Website: <>


Harvard School of Public Health.“Vitamins.” Harvard University, November 10, 2006. <>

Mayo Clinic Staff.“Dietary Supplements: Using Vitamin and Mineral Supplements Wisely.”, June 5, 2006. <>

supplements/NU00198/ Medline Plus.“Medline Encyclopedia: Vitamins.” U. S. National Library of Medicine, October 27, 2004. <http://www.nlm.nih/gov/medlineplus/ency/article/002399.htm/>

Tish Davidson, A.M.