La vitamin H, better defined biotin and sometimes also referred to as Vitamin B7 o white B8, is a vitamin water-soluble of complex B.
Note: the "informal" nomenclature of vitamins may vary by country, period or research organization; the term B7, for example, is also often used to define the inositol - for this reason it is always advisable to rely on the noun scientific, in this case "biotin".
Involved in a wide range of physiological processes, both in humans and in other organisms, it seems that vitamin H is linked above all to metabolism di grassi, carbohydrates e fundamental amino acids.
Her presence in foods it is almost ubiquitaria, even if bioavailable in foods of animal origin. In a varied and balanced diet, an eventual shortage nutritional turns out a lot rare for the subject healthy - with few exceptions. No side effects are known from toxicity food.
Vitamin H is composed from a ring ureido fused with a ring tetraidrotiofene. The ureid ring acts as vector of carbon dioxide in the carboxylation reactions.
Did you know ...
"H" stands for "Haar und Haut", German words for "hair and skin"
For several reasons - which we will see better below - in many countries DON'T one has been established quota of daily intake registered mail of vitamin H.
However, a so-called adequate intake (AI) - both by the US and European bodies - on the basis of the inke medium of the population, which seems to fully satisfy general needs.
For the US Institute of Medicine (IOM), the AIs of vitamin H for males and females (except those in pregnancy and breastfeeding) correspond to the following:
- 5 μg / day of biotin for infants aged 0-6 months
- 6 μg / day for children aged 7 to 12 months
- 8 μg / day for 1-3 year old children
- 12 μg / day for 4-8 year old children
- 20 μg / day for 9-13 year old children
- 25 μg / day for subjects aged 14-18 years
- 30 μg / day of biotin for those 19 years of age or older.
The AIs of Vitamin H for Women in pregnancy or nursing, respectively, are:
- 30 μg / day of biotin for pregnant women aged 14 to 50;
- 35 μg / day for breastfeeding women of the same age.
The European Food Safety Authority (EFSA) states that the adequate intake of vitamin H corresponds to 40 μg / die in pregnancy e 45 μg / die in nursing.
For children aged 1 to 17, the AIs increase with age from 20 to 35 μg / day.
Vitamin H is ubiquitaria ma bioavailable only in foods of animal origin, without which it is difficult guarantee i minimum levels recommended intake.
The intestinal bacteria of the microbiota (bacterial flora physiological) summarize ed espellono biotin in their metabolic processes, which then comes absorbed dall 'guest.
Biotin is stable a room temperature e DON'T is destroyed from cooking. Sources with valuable content are:
|Food||µg per serving||portion||µg per 100 g|
|Chicken liver, cooked||138||74 g||186,5|
|Pork or beef liver, cooked||above the 35||3 ounces|
|Chicken egg, cooked||above the 25||large egg||above the 200|
|Brewer's yeast, dry||spopra and 14||7 g|
|Avocado||above the 6||1 fruit||18 100|
|Peanuts, roasted, salted||can vary between
5 μg e 28 μg
|Salmon, cooked||above the 5||31 g||7,7|
|Sunflower seeds, roasted, salted||2,4|
It has been estimated that the dietary intake of vitamin H in Western populations goes up to 60 μg /die.
Digestion and Absorption
In order to properly absorb dietary biotin is necessary ensure one digestion Assessment of meals, as often it is bound a residue di Lysine (amino acid) that must be hydrolyzed from peptidasi pancreatica.
L'absorption of vitamin H occurs inintestine, more precisely in the fasting and in 'ileo proximal; the mechanisms are still poorly understood but it is plausible that its transition takes place for gradients di concentration thanks to sodium (Na).
As anticipated in the introduction, vitamin H is a component important of enzymes involved in various metabolic processes, such as digestion protein synthesis gluconeogenesis and growth cellular. It is also required for the catabolism and the use of the three chain amino acids branched: leucine, isoleucina e valina. Allows the synthesis of fatty acids and it seems Useful al maintenance homeostatic of the glycemia.
More precisely, the functions of vitamin H are type coenzyme-carbossilasi, enzymes belonging to the category of liaise and they stare a molecule of of CO2 and they transfer later in that da carboxylate; specifically, vitamin H is the coenzyme of 4 carbossilasi very important:
- Pyruvate carboxylase → gluconeogenesis
- Propionyl CoA carbossilasi → propionate metabolism
- Methylcrotonyl CoA → metabolism of branched chain amino acids
- Acetyl CoA carboxylase → synthesis of fatty acids.
Distribution in the Body
As can be deduced from the numerous metabolic functions of vitamin H, his concentration within the organism it must be evenly distributed; in fact, representing a coenzyme decisive in the carboxylation, vitamin H is required in all the body districts (in the form of biocitin) with particular density within the liver, in which the gluconeogenesis, metabolism of fundamental amino acids branched and synthesis acids grassi they are particularly active.
The mechanism of vehiculation of vitamin H DON'T è specific; it is found both in free form in plasma (20%) than fit tied ad albumin e globulins.
La shortage of vitamin H is very rare, especially in the adult. It can be caused by ainadequate dietary intake or more frequently frominheritance of one or more genetic disorders congenital affecting the metabolism of the same - such as the shortage of the enzyme HLCS (from English holocarboxylase synthetase) which covalently links biotin to carboxylase, in which vitamin H acts as a cofactor; the screening methods neonatal due to the deficiency of biotinidasi it started in the 80s.
Vitamin H deficiency occurs, among healthy individuals, with greatest frequency in suckler and in pregnancy; almost half of pregnant women show an abnormal increase in3-hydroxyisovaleric acid, which reflects the reduced state of biotin.
The deficit subclinico may cause mild symptoms of nature psychological e neurological, as trough, lethargy, hallucinations, numbness e tingling of the end. In the most severe paintings, the thinning to the hair (alopecia), nails fragile, L 'eruption cutaneous - usually on the face, or on the genitals - conjunctivitis.
Individuals with disorders hereditary have evidence of altered functionality System immune, including a major susceptibility infections bacterial e fungal.
On the other hand, it is more frequent that a defect of vitamin H intake in people with complications o abnormal conditions as:
- patients fed by way parenteral;
- suffering from malabsorption intestinal;
- subjects who habitually consume alone raw eggs as a food source of animal origin (some types of vegetarianism). This happens because of the action binding dell 'avidina, a protein contained in egg white which, if not previously denatured with cooking, hinders the absorption of vitamin H by acting as antinutrient.
L'excess nutritional value of vitamin H is unlikely, and with it his toxicity. neither il overdose to mouth (up to 10 mg / day) would seem capable of causing adverse reactions.
Vitamin H is often recommended as a dietary supplement for strengthen i hair and nails, although i scientific data in support of these results are weak. However, biotin is found in many cosmetics and products for the health to the hair and skin.