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Vitamins

A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound (or related set of compounds) is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and on the particular organism. For example, ascorbic acid (vitamin C) is a vitamin for humans, but not for most other animals, and biotin and vitamin D are required in the human diet only in certain circumstances. By convention, the term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids (which are needed in larger amounts than vitamins), nor does it encompass the large number of other nutrients that promote health but are otherwise required less often. Thirteen vitamins are presently universally recognized.
Vitamins are classified by their biological and chemical activity, not their structure. Thus, each “vitamin” refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin “generic descriptor” title, such as “vitamin A”, which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter-convertible to one another, as well.
Vitamins have diverse biochemical functions. Some have hormone-like functions as regulators of mineral metabolism (e.g., vitamin D), or regulators of cell and tissue growth and differentiation (e.g., some forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C).The largest number of vitamins (e.g., B complex vitamins) function as precursors for enzymecofactors, that help enzymes in their work as catalysts in metabolism. In this role, vitamins may be tightly bound to enzymes as part of prosthetic groups: For example, biotin is part of enzymes involved in making fatty acids. Vitamins may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. For example, folic acid carries various forms of carbon group – methyl, formyl, and methylene – in the cell. Although these roles in assisting enzyme-substrate reactions are vitamins’ best-known function, the other vitamin functions are equally important.
Until the mid-1930s, when the first commercial yeast-extract and semi-synthetic vitamin C supplement tablets were sold, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) can alter the types and amounts of vitamins ingested. Vitamins have been produced as commodity chemicals and made widely available as inexpensive semisynthetic and synthetic-source multivitamin dietary supplements, since the middle of the 20th century.
The term vitamin was derived from “vitamine,” a combination word made up by Polish scientist Casimir Funk from vital and amine, meaning amine of life, because it was suggested in 1912 that the organic micronutrient food factors that prevent beriberi and perhaps other similar dietary-deficiency diseases might be chemical amines. This proved incorrect for the micronutrient class, and the word was shortened to vitamin.

List of vitamins

Each vitamin is typically used in multiple reactions, and, therefore, most have multiple functions.

Vitamin Dosage Functions Natural Sources
Vitamin ARetinol and/orBeta Carotene 5000 – 50,000 IU Helps build healthy eyes, required for growth and bone development.Beta Caroteneis a good antioxidant. Helps healing of infections. Carrots, yams, pumpkins, yellow ororange fruits, beet greens, fish, eggs, tuna
Vitamin B1Thiamine 25 – 300mg Helps incarbohydrate metabolism and energy production. Required for normal nerve function. Whole grains, rice bran, lean meats, fresh peas, beans, wheat germ, oranges, poultry, fish, enriched pastas
Vitamin B2Riboflavin 25 – 300mg Helps in production of energy from foods and the formation of red blood cells. Fortified grains & cereals, leafy green vegetables, poultry, fish, yogurt, milk, cheese
Vitamin B3Niacin 25 – 300mg Assists in release of energy from carbohydrates, fats and proteins; helps promote healthy skin. Fortified breads and cereals, brewer’s yeast, broccoli, carrots, cheese, dandelion greens, dates, eggs, fish, milk peanuts, potatoes, tomatoes, tuna, veal,beef liver, chicken breast
Vitamin B5Pantothenic Acid 10 – 300 mg Helps release energy from foods; required for synthesis of many substances. Lean meats, whole grain cereals, fish, legumes
Vitamin B6 2 – 300 mg Essential forprotein metabolism and nervous system function; participates in synthesis of hormones and red blood cells. Whole grain breads and cereals, fish, chicken, bananas
Vitamin B9 Folic Acid 400 – 1,200 mcg Essential for red blood cell formation and synthesis of DNA and protein Fortified cereals, pinto beans, navy beans, green leafy vegetables, beef, brown rice, bran, cheese, lamb, liver, milk, mushrooms, oranges, split peas, pork, tuna, whole grains
Vitamin B12Cyanocobalamin 25 – 500 mg Helps maintain healthy nervous system, required for normal growth and for production of red blood cells. Helps breakdown fatty acids. Ham, clams, cooked oysters, king crab, herring, salmon, tuna, lean beef, liver, low fat diary products
Vitamin C 60 – 5,000 mg Required for formation of connective tissue, bones and teeth; assists in utilization of other vitamins, acts as an antioxidant. Citrus fruits, strawberries, broccoli, melons, peppers, collards, dandelion greens, onions, radishes, watercress
Vitamin D 400 – 800 IU Aides in normal bone growth and tooth function; facilitates calcium and phosphorus absorption. Sun exposure, sardines, salmon, fortified milk, fortified cereals, herring, liver, tuna, margarine, cod liver oil
Vitamin E 30- 1,200 IU As an antioxidant it protects body cells and helps maintain normal red blood cells. Whole grains, wheat germ, nuts, spinach, sunflower seeds
Vitamin H Biotin 0.3 – 1 mg Assists in metabolism of carbohydrates and synthesis of fats and proteins. Legumes, nuts
Vitamin K 80 mcg Essential in the blood clotting process. Green leafy vegetables like kale, spinach, broccoli, cauliflower

In nutrition and diseases

Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a fetus begins to develop, at the moment of conception, from the nutrients it absorbs. It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage.

For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine — commonly known as “gut flora” — produce vitamin K and biotin, while one form of vitamin D is synthesized in theskin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.

Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.

Deficiencies

It was suggested that, when plants and animals began to transfer from the sea to rivers and land about 500 million years ago, environmental deficiency of marine mineral antioxidants was a challenge to the evolution of terrestrial life. Terrestrial plants slowly optimized the production of “new” endogenous antioxidants such as ascorbic acid (Vitamin C), polyphenols, flavonoids, tocopherols, etc. Since this age, dietary vitamin deficiencies appeared in terrestrial animals. Humans must consume vitamins periodically but with differing schedules, to avoid deficiency. Human bodily stores for different vitamins vary widely; vitamins A, D, and B12 are stored in significant amounts in the human body, mainly in the liver,and an adult human’s diet may be deficient in vitamins A and D for many months and B12 in some cases for years, before developing a deficiency condition. However, vitamin B3 (niacin and niacinamide) is not stored in the human body in significant amounts, so stores may last only a couple of weeks. For vitamin C, the first symptoms of scurvy in experimental studies of complete vitamin C deprivation in humans have varied widely, from a month to more than six months, depending on previous dietary history that determined body stores.

Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when an organism does not get enough of the vitamin in its food. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, due to a “lifestyle factor”, such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or use of the vitamin. People who eat a varied diet are unlikely to develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases.

Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy), and vitamin D (rickets). In much of the developed world, such deficiencies are rare; this is due to (1) an adequate supply of food and (2) the addition of vitamins and minerals to common foods, often called fortification. In addition to these classical vitamin deficiency diseases, some evidence has also suggested links between vitamin deficiency and a number of different disorders.

Side-effects and overdose

In large doses, some vitamins have documented side-effects that tend to be more severe with a larger dosage. The likelihood of consuming too much of any vitamin from food is remote, but overdosing (vitamin poisoning) from vitamin supplementation does occur. At high enough dosages, some vitamins cause side-effects such as nausea, diarrhea, and vomiting. When side-effects emerge, recovery is often accomplished by reducing the dosage. The doses of vitamins different individual can tolerate varies widely, and appear to be related to age and state of health.

In 2008, overdose exposure to all formulations of vitamins and multivitamin-mineral formulations was reported by 68,911 individuals to the American Association of Poison Control Centers (nearly 80% of these exposures were in children under the age of 6), leading to 8 “major” life-threatening outcomes and 0 deaths.[38]