Vitamin

See also: Vitamin (homonymy)

A vitamin is a substance organic, necessary in infinitesimal amount to the Métabolisme of the animal organizations and thus of the man. The vitamins are essential complements of the vital exchanges. It is an organic molecule, a Coenzyme (molecule which takes part in the active site of an enzyme), which contains one or more radicals essential to the synthesis of a Enzyme or a Hormone. The organization not being able to synthesize them, or in insufficient quantity, they must be brought regularly and in sufficient quantity by the food. At the human being, only three vitamins are synthesized by intestinal bacteria: the vitamins K, B₁₂ and H.

An insufficient contribution or an absence of vitamin respectively causes a Hypovitaminose or a Avitaminose which are the cause of various diseases (Scorbut, Béribéri, Rachitisme, etc), an excessive contribution of liposoluble vitamins (has and D primarily) causes a Hypervitaminose, very poison for the organization.

Their discovery is due to the Polish biochemist Kazimierz Funk which, the first, isolated the vitamin B₁ in the envelope from rice in 1912. The term “vitamin” comes from Latin “vita” which means life and from the suffix amine .

Classification of the vitamins

Generally, the vitamins in two groups are separated: the water-soluble vitamins (water soluble) and the liposoluble vitamins (soluble in greases).

The liposoluble vitamins are absorbed with greases and, like those, are storable in the organization. Contrary, the water-soluble vitamins (except for the B₁₂ vitamin) are not storable and the surplus contributions are eliminated by the urinary tract.

Water-soluble vitamins

Liposoluble vitamins

Ex-vitamins

The fatty-acids had been originally regarded as vitamins (F). They are not classified any more in this category today (because of quantity of daily contribution between 2 and 3 grams per day on average for the adult, and of pathogenic action in the event of excess).

Requirements in vitamins

They are difficult to establish because they vary with the age, the size, the sex, the muscular activity. They increase during the growth, during the feverish diseases and states, and with regard to the women, during the pregnancy and breast feeding.

Certain specialists and researchers established what they call the Daily Optimal (AOJ) Apport. These values are higher and have a preventive effect on certain diseases. These values do not concern the expectant mothers, during the breast feeding or the people taking of the drugs (drawn from www.DrLam.com).

A more complete table is here: Table of proportionings recommended and optimal

Goings beyond of amount

The going beyond of the amounts recommended in the industrialized countries is frequent for certain vitamins in particular the Vitamine C used by industry like antioxydant (preserving). The overdoses also intervene because of the consumption of food complements and pills “anti-ageing” or Bronzage. Indeed, of many people vitamins in the form of pill consume, in particular for their effects Antioxydant and of elimination of the free radical ; however, certain vitamins generate they even free radicals. According to a study of the Newspaper off American Medical Association , the overconsumption of β-carotene and vitamins has and E, which is not eliminated by the urines, increases the mortality by respectively 7%,16% and 4%. If there exist deficiencies of vitamin in the underprivileged populations of the industrialized countries, they are on the other hand the people not presenting a deficiency who consume food complements.
The vitamin C is eliminated by the Rein S as soon as it exceeds a certain threshold, and a surdose was thus regarded as inoffensive. It is estimated however today that this elimination, if it is prolonged over several months, can involve renal calculi at certain subjects.
A study would show that the excess of vitamin has multiplies by 2,5 the risks of fracture of the hip. This dangerous effect is more Net with the rétinol (vitamin has itself) that with the β-carotene (provitamin A).
Above 400 mg/jour (instead of 2), the B₆ vitamin can cause nervous lesions.
The harmful effects of the surdose of vitamin D are known for a long time: renal and cardiac accidents serious. However, a surdose appears only starting from one catch day laborer of quantity equalizes with more than 100 times the daily contribution recommended and this over several months.
Other accidents of overdose exist with the B₁ vitamin and the vitamin K.

See also: Hypervitaminose

Action of the vitamins
The crucial role of a vitamin consists of a transfer of a Molécule towards another, of a electron of a Atome (or a limited group of atoms) towards another, according to processes which one can compare to enzymatic phenomena.
One can define the general activity of the vitamins according to their interest or a scientific classification.
; Classification according to their interest

the reduction or even suppression of certain specific reactions of a metabolic chain, which the absence or the reduction of the vitamin contribution can involve.

the physiological action which the vitamins have. For example:

the vitamin C and its role in the phenomena of capillary permeability.

folic acid and its role in the hématopoïèse.

; Scientific classification

Vitamines whose role is to transport the electrons, like the vitamins B₂ and B₃.

Vitamines whose role is to transport free radicals like the vitamins B₁ and B₆.

Conservation of the vitamins

The majority of the vitamins are destroyed by heat, the air and the rays Ultraviolet S. For example, the cooking of a food eliminates approximately 50% from the vitamins.
In addition, the water-soluble vitamins leave mainly in water cooking. Thus, a Soup or a Soup, for which one keeps water, or the Cuisson with the vapor, with which the food does not soak in water, makes it possible to keep a greater quantity of vitamins.

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