VITAMINS

Vitamins are substances that are essential in certain chemical transformations in the human body. They help the body process proteins, carbohydrates, and fats. Certain vitamins also contribute to the production of blood cells, hormones, genetic material, and chemicals of the nervous system.

Vitamins exist in minute quantities in food. Most vitamins cannot be produced by the body and must be obtained through the diet. Since no single food item or nutrient class provides all the essential vitamins, it is necessary to eat a variety of foods. For example, vitamin A is needed for the eyes and to keep the linings of the bronchial, urinary, and intestinal tracts healthy; vitamin C is needed for the development of bones, teeth, blood vessels, and other tissues; vitamin K is necessary for blood clotting; and vitamin D is also needed for the development of bones and teeth.

The principal vitamins are: vitamin A, vitamin B₁, vitamin B₂, pantothenic acid (part of the B₂ complex), vitamin B₃, vitamin B₆, folic acid, vitamin B₁₂, vitamin C, vitamin D, vitamin E, vitamin H (often considered part of the B-vitamin group), and vitamin K.

Some vitamins (e.g., vitamin K) are produced by intestinal bacteria, and a few can be formed by the body from substances called provitamins (portions of vitamins that can be assembled or modified by the body into functional vitamins). Carotene is an example of a provitamin that can be modified by the body to form vitamin A. Vitamins are used by the body in their original or slightly modified forms. Once the chemical structure of a vitamin is destroyed, its function is usually lost. The chemical structure of many vitamins is destroyed by heat (e.g., when food is overcooked).

There are two major classes of vitamins: fat soluble and water soluble. Fat-soluble vitamins such as vitamins A, D, E, and K are absorbed from the intestine along with lipids, and some of them can be stored in the body for a long period of time. Because they can be stored, it is possible to accumulate an overdose of these vitamins in the body (hypervitaminosis) to the point of toxicity. Water-soluble vitamins such as the B complex and C are absorbed with water from the intestinal tract and remain in the body only a short time before excreted.

The absence of a specific vitamin in the diet can result in a specific deficiency disease.

Vitamins are compounds that you must have to growth and health. They are needed in small amounts only and are usually available in the foods that you eat. Vitamin A is necessary for normal growth and health and for healthy eyes and skin. Lack of vitamin A may lead to a rare condition called night blindness (problems seeing in the dark), as well as dry eyes, eye infections, skin problems, and slowed growth. Your physician may treat these problems by prescribing vitamin A for you. Vitamin A is found in various foods including yellow-orange fruits and vegetables; dark green, leafy vegetables; whole milk; and margarine. Vitamin A comes in different forms. The form of vitamin A found in plants is called beta-carotene. Food processing may destroy some of the vitamins. For example freezing may reduce the amount of vitamin A in foods. Vitamin A is stored in the body and taking too much over a period of time can cause poisoning.

Vitamin B₂ (riboflavin) is necessary for normal metabolism. Lack of vitamin B₂ may lead to itching and burning eyes, sensitivity of eyes to light, sore tongue, itching skin on the nose, and sores in the mouth. Vitamin B₂ is found in various foods, including milk and dairy products, fish, meat, green leafy vegetables, and whole grain and enriched cereals and bread.

Vitamin B₁₂ is necessary for healthy blood. Cyanocobalamin and hydroxocobalamin are man-made forms of vitamin B₁₂. Lack of vitamin B₁₂ may lead to anemia, stomach problems, and nerve damage. Vitamin B₁₂ is found in various foods, including fish, egg yolk, milk, and fermented cheeses. It is not found in any vegetables.

Vitamin E prevents a chemical reaction called oxidation, which can sometimes result in harmful effects in the human body. Lack of vitamin E is extremely rare, except in people who have a disease in which it is not absorbed into the body. Vitamin E is found in various foods including vegetable oils (corn, soybean), wheat germ, whole-grain cereals, and green leafy vegetables. Vitamin E is stored in the body and taking too much over a period of time may cause harmful effects.

Vitamin K is necessary for normal clotting of the blood. Vitamin K is found in various foods including green leafy vegetables, meat, and dairy products. If you eat a balanced diet containing these foods, you should be getting all the vitamin K you need. Little vitamin K is lost from foods with ordinary cooking. Lack of vitamin K is rare but may lead to problems with blood clotting and increased bleeding. Vitamin K is routinely given to newborn infants to prevent bleeding problems. It is found in spinach, vegetable oils, and cabbage.

Vitamin D is necessary for strong bones and teeth. Lack of vitamin D may lead to a condition called rickets, especially in children, in which bones and teeth are weak. In adults it may cause a condition called osteomalacia, in which calcium is lost from bones so that they become weak. Vitamin D is sometimes used to treat other diseases in which calcium is not used properly by the body. Vitamin D is found naturally only in fish and fish-liver oils. However, it is also found in other foods such as milk and bread to which it has been added. Cooking does not affect the vitamin D in foods. Vitamin D is sometimes called the “sunshine vitamin” since it is made in the skin when the human is exposed to sunlight. If you eat a balanced diet and get outside in the sunshine, you should be getting all the vitamin D you need.