Vitamins are essential in the diet because the body does
not produce enough of them, or may not produce them at all.
There are thirteen different vitamins, A, eight B-complex vitamins, C, D, E, and K.
Since the body (for the most part) is unable to make vitamins, they must be supplied in the daily diet or through supplements. One vitamin, Vitamin D, is produced in the skin when it is exposed to the sun's rays. Vitamin K is not made by the body at all, but is formed by microorganisms in the intestinal tract only when green, leafy vegetables and vegetable oils are eaten.
The body's vitamin requirements are expressed in terms of recommended dietary allowances, or RDAs. These amounts are considered to be sufficient by the established medical community, but I suspect they will learn that we need more or need different nutrients than they presently think we do.
Proteins, carbohydrates, and fats combine with other substances to furnish energy and build tissues. These chemical reactions are enhanced by enzymes produced by certain vitamins, and they take place in specific parts of the body.
The vitamins we need are divided into two categories: water-soluble vitamins (the B vitamins and vitamin C) and fat-soluble vitamins (A, D, E, and K).
The water-soluble vitamins are absorbed by the intestine and carried by the circulatory system to the specific tissues where they will be put into use. If one takes too much of a water-soluble vitian, the excess is excreted from the body. Since the body does not store them, we need a daily intake from outside sources.
Fat-soluble vitamins are different. The intestine absorbs them, and the lymph system carries these vitamins to different parts of the body. The Fat-solubles are involved in maintaining the structure of cell membranes, and it is also believed that fat-soluble vitamins are responsible for the synthesis of certain enzymes.
The liver is the main storehouse for vitamins A and D, while vitamin E is stored in body fat and to a lesser extent in reproductive organs. Relatively little vitamin K is stored. Excessive intake of fat-soluble vitamins, specifically A and D, can lead to toxic levels in the body, so here we must be cautious.
Vitamins are found only in plants - except Vitamin D, which comes from animal sources.
Vitamin A (retinol) is a fat-soluble
vitamin that is easily destroyed upon exposure to heat, light, or air. It is essential
for the proper functioning of most body organs and also affects the functioning
of the immune system. It also has a direct role in vision.
Vitamin A deficiency results in various disorders that most commonly involve the eye and the epithelial tissues the skin and the mucous membranes lining the internal body surfaces. An early symptom of vitamin A deficiency is the development of night blindness, and continued deficiency eventually results in loss of sight. If deficiency is prolonged, the skin may become dry and rough. Vitamin A deficiency may also result in defective bone and teeth formation.
Excessive intake of vitamin A causes a toxic condition, whose symptoms can include nausea, coarsening and loss of hair, drying and scaling of the skin, bone pain, fatigue, and drowsiness. There may also be blurred vision and headache in adults, and growth failure, enlargement of the liver, and nervous irritability in children.
Vitamin B complex consists of several vitamins that are grouped together because of the loose similarities in their properties, distribution in natural sources, and physiological functions. They all appear to be essential in facilitating the metabolic processes of all forms of animal life. The complex includes B1 (thiamine), B2 (riboflavin), niacin (nicotinic acid), B6 (a group of related pyridines), B12 (cyanocobalamin), folic acid, pantothenic acid, and biotin.
Vitamin C (ascorbic acid) is water-soluble and easily destroyed. It is essential in wound healing and in the formation of collagen, a protein important in the formation of healthy skin, tendons, bones, and supportive tissues. Deficiency results in defective collagen formation and is marked by joint pains, irritability, growth retardation, anemia, shortness of breath, and increased susceptibility to infection. Scurvy is the classic disease related to deficiency. Symptoms peculiar to infantile scurvy include swelling of the lower extremities, pain upon flexing them, and bone lesions. Excessive ascorbic-acid intake can cause kidney stones, gastrointestinal disturbances, and red-blood-cell destruction.
Vitamin D is a fat-soluble compound essential for calcium metabolism in animals and therefore important for normal mineralization of bone and cartilage. The skin forms vitamin D when exposed to sunlight, but in some circumstances sunlight may lack sufficient amounts of ultraviolet rays to bring about adequate production of the vitamin.
Deficiencies cause many biochemical and physiological imbalances. If uncorrected, faulty mineralization of bones and teeth causes rickets in growing children and osteomalacia (progressive loss of calcium and phosphorus from the bones) in adults. Common early symptoms of rickets include restlessness, profuse sweating, lack of muscle tone in the limbs and abdomen, and delay in learning to sit, crawl, and walk. Rickets may produce such conditions as bowlegs and knock-knees. Deficiency may also cause osteoporosis, a bone condition characterized by an increased tendency of the bones to fracture. Large doses of vitamin D are toxic, and symptoms include weakness, loss of appetite, nausea, vomiting, diarrhea, excessive thirst, and weight loss.
Vitamin E is a fat-soluble compound. The metabolic roles of this vitamin are poorly understood. Its primary role appears to be as an inhibitor of oxidation processes in body tissues. Deficiency is rare but may impair neuromuscular function. Although serious toxicity has not been attributed to large doses of vitamin E, adverse effects have been reported.
Vitamin K is fat-soluble and essential for the synthesis of certain proteins necessary for the clotting of blood. Deficiency, though relatively uncommon, results in impaired clotting of the blood and internal bleeding.
[condensed from an article by Manisha Harisingh Maskay, Ph.D., Health Education Coordinator and Clinical Nutritionist, University of Chicago]
& Hobbies & Links, Oh My!
Avian Critter || Canine Critter
Human Critters || Wild Critters
background/hr by me: Papagei Studios