Vitamins are a group of substances essential for normal cell function, growth and development.

There are 13 essential vitamins. That means they are needed for the body to function. They are:

• Vitamin A
• Vitamin C
• Vitamin D
• Vitamin E
• Vitamin K
• Vitamin B1 (thiamine)
• Vitamin B2 (riboflavin)
• Vitamin B3 (niacin)
• Pantothenic acid
• Biotin
• Vitamin B6
• Vitamin B12
• Folate (folic acid)

Vitamins are grouped into two categories:

• Fat-soluble vitamins are stored in the body's fatty tissue.
• Water-soluble vitamins must be used by the body right away. Any left over water-soluble vitamins leave the body through the urine. Vitamin B12 is the only water-soluble vitamin that can be stored in the liver for many years.

Each vitamin has specific functions. You can develop health problems (deficiency disease) if you do not get enough of a particular vitamin.

Vitamin A helps form and maintain healthy teeth, bones, soft tissue, mucous membranes, and skin.

Vitamin B6 is also called pyridoxine. The more protein you eat, the more vitamin B6 is needed to help the body use protein. Vitamin B6 helps form red blood cells and maintain brain function, among other things.

Vitamin B12, like the other B vitamins, is important for metabolism. It also helps form red blood cells and maintain the central nervous system.

Vitamin C, also called ascorbic acid, is an antioxidant that promotes healthy teeth and gums. It helps the body absorb iron and maintain healthy tissue. It also promotes wound healing.

Vitamin D is also known as the "sunshine vitamin," since it is made by the body after being in the sun. Ten to 15 minutes of sunshine 3 times a week is enough to produce the body's requirement of vitamin D. However, many people living in sunny climates still do not make enough vitamin D and need more from their diet or supplements. Vitamin D helps the body absorb calcium, which you need for the normal development and maintenance of healthy teeth and bones. It also helps maintain proper blood levels of calcium and phosphorus.

Vitamin E is an antioxidant also known as tocopherol. It plays a role in the formation of red blood cells and helps the body use vitamin K.

Vitamin K is not listed among the essential vitamins, but without it blood would not stick together (coagulate). Some studies suggest that it helps promote strong bones in the elderly.

Biotin is essential for the metabolism of proteins and carbohydrates, and in the production of hormones and cholesterol.

Niacin is a B vitamin that helps maintain healthy skin and nerves. It is also has cholesterol-lowering effects.

Folate works with vitamin B12 to help form red blood cells. It is necessary for the production of DNA, which controls tissue growth and cell function. Any woman who is pregnant should be sure to get enough folate. Low levels of folate are linked to birth defects such as spina bifida. Many foods are now fortified with folic acid.

Pantothenic acid is essential for the metabolism of food. It is also plays a role in the production of hormones and cholesterol.

Riboflavin (B2) works with the other B vitamins. It is important for body growth and the production of red blood cells.

Thiamine (B1) helps the body cells change carbohydrates into energy. It is also essential for heart function and healthy nerve cells.

FAT-SOLUBLE VITAMINS

Vitamin A:

• Eggs
• Meat
• Milk
• Cheese
• Cream
• Liver
• Kidney
• Cod
• Halibut fish oil

Vitamin D:

• Cheese
• Butter
• Margarine
• Cream
• Fortified milk
• Fish
• Oysters
• Cereals

Vitamin E:

• Wheat germ
• Corn
• Nuts
• Seeds
• Olives
• Spinach and other green leafy vegetables
• Asparagus
• Vegetable oils and products made from vegetable oils, such as margarine

Vitamin K:

• Cabbage
• Cauliflower
• Spinach
• Soybeans
• Cereals

WATER-SOLUBLE VITAMINS

Folate:

• Green, leafy vegetables
• Fortified foods

Niacin (B3):

• Dairy products
• Poultry
• Fish
• Lean meats
• Nuts
• Eggs
• Legumes
• Enriched breads and cereals

Pantothenic acid and biotin

• Eggs
• Fish
• Dairy products
• Whole-grain cereals
• Legumes
• Yeast
• Broccoli and other vegetables in the cabbage family
• White and sweet potatoes
• Lean beef

Thiamine (B1):

• Fortified breads, cereals, and pasta
• Whole grains
• Lean meats
• Fish
• Dried beans
• Peas
• Soybeans
• Dairy products
• Fruits and vegetables

Vitamin B12:

• Meat
• Eggs
• Poultry
• Shellfish
• Milk and milk products

Vitamin C (ascorbic acid)

• Citrus fruits and juices
• Strawberries
• Tomatoes
• Broccoli
• Turnip and other greens
• Sweet and white potatoes
• Cantaloupe

Most other fruits and vegetables contain some vitamin C; fish and milk contain small amounts.

Many people think that if some is good, a lot is better. This is not always the case. High doses of certain vitamins can be poisonous. Ask your doctor what is best for you.

The Food and Nutrition Board at the Institute of Medicine establish recommended dietary allowances (RDAs) for vitamins. The recommendations reflect how much of each nutrient you should receive on a daily basis, based on the known nutritional needs of practically all healthy people.

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy).

Hamrick I, Counts SH. Vitamin and mineral supplements. Wellness and Prevention. December 2008:35(4);729-747.

Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 237.

Anderson RA. Prescribing antioxidants. In: Rakel D, ed. Integrative Medicine. 2nd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 103.