Vitamins

Vitamins are substances the body needs in small amounts to support most body functions and prevent disease. Vitamins play a role in energy production and growth; and work with each other and with other nutrients to keep our hearts pumping, our bones and immune system strong, our digestive system moving and our skin and hair healthy. The 13 vitamins are divided into two groups:

Water-soluble vitamins include members of the B complex (thiamin, riboflavin, niacin, vitamin B6, folic acid, vitamin B12, pantothenic acid, biotin) and vitamin C. Most water-soluble vitamins support enzyme systems in the body. Although the vitamins themselves don't provide energy, many are required for chemical reactions that do produce energy. Water-soluble vitamins are sensitive to heat and are easily broken down during cooking. Except for vitamin B12, they aren't stored in the body in appreciable amounts. They must be replenished regularly through the food we eat. On the other hand, they are unlikely to build up to toxic levels.

Fat-soluble vitamins include A, D, E and K. Vitamin A supports night vision and keeps skin healthy. Vitamin D helps the body absorb and use calcium, which is essential for healthy bones. Vitamin E keeps red blood cells healthy and maintains all body tissues. Vitamin K helps blood clot and may play a role in skeletal health. Your daily diet should supply these vitamins; but since fat-soluble vitamins are stored in the body, it's possible to achieve toxic levels of vitamins A and D if you take supplements. Listed below are the functions and best sources for the 13 Vitamins:

Vitamin A
Needed for: Eye health, retinal function in dim light only; immune system; maintains healthy skin and mucous membranes; aids in tissue growth and repair

Best food sources: Foods contain very little vitamin A. The foods listed below are rich in carotene, which is converted to vitamin A in the intestine. Orange, red and yellow fruits and vegetables such as carrots, sweet potatoes, tomatoes and cantaloupe; green leafy vegetables such as spinach and broccoli.

Vitamin B1 (Thiamin)
Needed for: Normal function of the heart, nerves, muscle tissue and digestive system; aids in carbohydrate metabolism and energy production.

Best food sources: Lean meat, enriched and fortified cereals and baked goods, legumes and nuts.

Vitamin B2 (Riboflavin)
Needed for: Energy production, immune system function, healthy skin.

Best food sources: Low-fat dairy products, lean meat, eggs, enriched and fortified cereals and baked goods and green leafy vegetables.

Vitamin B3 (Niacin)
Needed for: Energy production, healthy skin, and digestive system function. The body can manufacture niacin from the amino acid tryptophan.

Best food sources: Lean meat, pork, veal, tuna, halibut, poultry, legumes, nuts and enriched and fortified cereals, yeast, baked goods, as well as coffee and tea.

Vitamin B6 (Pyrodoxine)
Need for: Energy production, red blood cell formation, immunity, nervous system and hormone function.

Best food sources: Lean beef, tuna, halibut, legumes, enriched and fortified cereals and baked goods, leafy green vegetables.

Vitamin B12
Needed for: Energy production, red blood cell production, utilization of folic acid, nervous system function.

Best food sources: Lean meat, poultry, fish, eggs, low-fat dairy products.

Folic acid
Needed for: Energy production, red blood cell formation and growth. Essential for prevention of certain birth defects.

Best food sources: Lean meat, fish, legumes, nuts, leafy green vegetables, whole grains.

Pantothenic acid
Needed for: Carbohydrate, fat, energy and protein metabolism.

Best food sources: Lean meat, fish, poultry, legumes, whole-grain cereals; widespread in the food supply.

Biotin
Needed for: Energy production, fatty acid synthesis and the breakdown of certain amino acids.

Best food sources: Widespread in the food supply; especially concentrated in egg yolks, liver, mushrooms, peanuts, yeast, milk, meat and most vegetables.

Vitamin C (Ascorbic acid)
Needed for: Normal growth, wound healing, disease and infection resistance, bone and teeth formation, more efficient iron absorption.

Best food sources: Citrus fruits, berries, potatoes, tomatoes, sweet and hot peppers, leafy green vegetables.

Vitamin D
Needed for: Normal growth; healthy bones, teeth and nails; proper absorption of calcium and phosphorus.

Best food sources: Fortified milk and milk products. (Vitamin D is also synthesized in the skin when exposed to sunlight.)

Vitamin E (tocopherol)
Needed for: Cell membrane integrity and protection.

Best food sources: Vegetable oils, margarine, eggs, fish, whole-grain cereals, dried beans.

Vitamin K
Needed for: Production of proteins required for normal blood clotting.

Best food sources: Leafy green vegetables and cereals; also synthesized in the digestive tract.

In addition to their other roles, vitamins C, E and beta-carotene (which the body converts into vitamin A) are known as "antioxidants." Certain minerals and other substances also act as antioxidants. Antioxidants can offset the damage caused by free radicals, the unstable, highly reactive molecules formed during the metabolism of glucose and fatty acids to provide energy. Free radicals are also produced in the body by pollutants, ultraviolet light from the sun and drinking alcohol. Free radicals react with and damage many components of tissues, including cellular DNA, or genetic material. Damage from free radicals may lead to conditions such as cataracts, cancer, heart disease and even aging.

What is not completely understood is why antioxidants in food are effective, but antioxidants taken as vitamin supplements have shown disappointing results. Not only does beta-carotene and vitamin E not protect smokers against lung cancer, a study in those who continued to smoke showed that taking beta-carotene actually increased lung cancer risk. And a 2001 New England Journal of Medicine article indicated that taking vitamin E, vitamin C and selenium offset the beneficial effects of cholesterol lowering medication in heart disease.

Although the health benefits of antioxidant supplements remain in question, a diet that contains lots of fresh fruits and vegetables provides the body with antioxidants and helps protect against cancer and heart disease.