Names | |
---|---|
Preferred IUPAC name 5-[(3aS,4S,6aR)-2-Oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid | |
Other names Vitamin B7 | |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChEMBL | |
ChemSpider | |
DrugBank | |
ECHA InfoCard | 100.000.363 |
KEGG | |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
| |
| |
Properties | |
C10H16N2O3S | |
Molar mass | 244.31 g·mol−1 |
Appearance | White crystalline needles |
Melting point | 232 to 233 °C (450 to 451 °F; 505 to 506 K) |
22 mg/100 mL | |
Pharmacology | |
A11HA05 ( WHO ) | |
Hazards | |
NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Biotin (also known as vitamin B7 or vitamin H) is one of the B vitamins. [1] [2] [3] It is involved in a wide range of metabolic processes, both in humans and in other organisms, primarily related to the utilization of fats, carbohydrates, and amino acids. [4] The name biotin, borrowed from the German Biotin, derives from the Ancient Greek word βίοτος (bíotos; 'life') and the suffix "-in" (a suffix used in chemistry usually to indicate 'forming'). [5] Biotin appears as a white, needle-like crystalline solid. [6]
Biotin is classified as a heterocyclic compound, with a sulfur-containing tetrahydrothiophene ring fused to a ureido group. A C5-carboxylic acid side chain is appended to the former ring. The ureido ring, containing the −N−CO−N− group, serves as the carbon dioxide carrier in carboxylation reactions. [7] Biotin is a coenzyme for five carboxylase enzymes, which are involved in the catabolism of amino acids and fatty acids, synthesis of fatty acids, and gluconeogenesis. [3] [4] Biotinylation of histone proteins in nuclear chromatin plays a role in chromatin stability and gene expression. [4] [8]
The US National Academy of Medicine updated Dietary Reference Intakes for many vitamins in 1998. At that time there was insufficient information to establish estimated average requirement or recommended dietary allowance, terms that exist for most vitamins. In instances such as this, the academy sets adequate intakes (AIs) with the understanding that at some later date, when the physiological effects of biotin are better understood, AIs will be replaced by more exact information. The biotin AIs for both males and females are:
Age Group | Biotin AI (μg/day) |
---|---|
0 to 6 months | 5 |
7 to 12 months | 6 |
1 to 3 years | 8 |
4 to 8 years | 12 |
9 to 13 years | 20 |
14 to 18 years | 25 |
19 years and older | 30 |
Pregnant females (14 to 50 years) | 30 |
Lactating females (14 to 50 years) | 35 |
Australia and New Zealand set AIs similar to the US. [9]
The European Food Safety Authority (EFSA) also identifies AIs, setting values at 40 μg/day for adults, pregnancy at 40 μg/day, and breastfeeding at 45 μg/day. For children ages 1–17 years, the AIs increase with age from 20 to 35 μg/day. [10]
The US National Academy of Medicine estimates upper limits for vitamins and minerals when evidence for a true limit is sufficient. For biotin, however, there is no upper limit because adverse effects of high biotin intake have not been determined. [2] The EFSA also reviewed safety and reached the same conclusion as in the United States. [11]
For US food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of daily value. For biotin labeling purposes, 100% of the daily value was 300 μg/day, but as of May 27, 2016, it was revised to 30 μg/day to bring it into an agreement with the adequate intake. [12] [13] Compliance with the updated labeling regulations was required by January 1, 2020, for manufacturers with US$10 million or more in annual food sales, and by January 1, 2021, for manufacturers with lower volume food sales. [14] [15] A table of the old and new adult daily values is provided at Reference Daily Intake.
Source [16] | Amount (μg / 100 g) |
---|---|
Chicken liver | 187 |
Beef liver | 42 |
Eggs | 21 |
Egg white | 5.8 |
Egg yolk | 27 |
Salmon, canned in water | 5.9 |
Pork chop | 4.5 |
Turkey breast | 0.7 |
Tuna, white, canned | 0.7 |
Source [16] | Amount (μg / 100 g) |
---|---|
Peanuts, roasted | 17.5 |
Sunflower seeds, roasted | 7.8 |
Almonds, roasted | 4.4 |
Sweet potato | 1.5 |
Broccoli | 0.9 |
Tomato | 0.7 |
Strawberry | 1.5 |
Avocado | 1.0 |
Corn, canned | 0.05 |
Source [16] | Amount (μg / 100 g) |
---|---|
Cheese | 1.4 |
Milk | 0.1 |
Oatmeal | 0.1 |
Bread | 0.1 |
French fries | 0.3 |
Wine | 0.1 |
Beer | 0.1 |
Potatoes, mashed | 0.1 |
Biotin is stable at room temperature and is not destroyed by cooking. The dietary biotin intake in Western populations has been estimated to be in the range of 35 to 70 μg/day. Nursing infants ingest about 6 μg/day. [4] Biotin is available in dietary supplements, individually or as an ingredient in multivitamins. [1] [3]
According to the Global Fortification Data Exchange, biotin deficiency is so rare that no countries require that foods be fortified. [17]
Biotin is a water-soluble B vitamin. Consumption of large amounts as a dietary supplement results in absorption, followed by excretion into urine as biotin. Consumption of biotin as part of a normal diet results in urinary excretion of biotin and biotin metabolites. [4]
Biotin in food is bound to proteins. Digestive enzymes reduce the proteins to biotin-bound peptides. The intestinal enzyme biotinidase, found in pancreatic secretions and in the brush border membranes of all three parts of the small intestine, frees biotin, which is then absorbed from the small intestine. [4] When consumed as a biotin dietary supplement, absorption is nonsaturable, meaning that even very high amounts are absorbed effectively. Transport across the jejunum is faster than across the ileum. [4]
The large intestine microbiota synthesize amounts of biotin estimated to be similar to the amount taken in the diet, and a significant portion of this biotin exists in the free (protein-unbound) form and, thus, is available for absorption. How much is absorbed in humans is unknown, although a review did report that human epithelial cells of the colon in vitro demonstrated an ability to uptake biotin. [18]
Once absorbed, sodium-dependent multivitamin transporter (SMVT) mediates biotin uptake into the liver. [4] SMVT also binds pantothenic acid, so high intakes of either of these vitamins can interfere with transport of the other. [19]
Biotin catabolism occurs via two pathways. In one, the valeric acid sidechain is cleaved, resulting in bisnorbiotin. In the other pathway, the sulfur is oxidized, resulting in biotin sulfoxide. Urine content is proportionally about half biotin, plus bisnorbiotin, biotin sulfoxide, and small amounts of other metabolites. [4]
Chronic alcohol use is associated with a significant reduction in plasma biotin. [20] Intestinal biotin uptake also appears to be sensitive to the effect of the anti-epilepsy drugs carbamazepine and primidone. [20] Relatively low levels of biotin have also been reported in the urine or plasma of patients who have had a partial gastrectomy or have other causes of achlorhydria, as well as burn patients, elderly individuals, and athletes. [21] Pregnancy and lactation may be associated with an increased demand for biotin. In pregnancy, this may be due to a possible acceleration of biotin catabolism, whereas, in lactation, the higher demand has yet to be elucidated. Recent studies have shown marginal biotin deficiency can be present in human gestation, as evidenced by increased urinary excretion of 3-hydroxyisovaleric acid, decreased urinary excretion of biotin and bisnorbiotin, and decreased plasma concentration of biotin. [4]
Biotin, synthesized in plants, is essential to plant growth and development. [22] Bacteria also synthesize biotin, [23] and it is thought that bacteria resident in the large intestine may synthesize biotin that is absorbed and utilized by the host organism. [18]
Biosynthesis starts from two precursors, alanine and pimeloyl-CoA. These form 7-keto-8-aminopelargonic acid (KAPA). KAPA is transported from plant peroxisomes to mitochondria where it is converted to 7,8-diaminopelargonic acid (DAPA) with the help of the enzyme, BioA. The enzyme dethiobiotin synthetase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP, creating dethiobiotin with the help of the enzyme, BioD, which is then converted into biotin which is catalyzed by BioB. [24] The last step is catalyzed by biotin synthase, a radical SAM enzyme. The sulfur is donated by an unusual [2Fe-2S] ferredoxin. [25] Depending on the species of bacteria, Biotin can be synthesized via multiple pathways. [24]
The enzyme holocarboxylase synthetase covalently attaches biotin to five human carboxylase enzymes: [4]
For the first two, biotin serves as a cofactor responsible for transfer of bicarbonate to acetyl-CoA, converting it to malonyl-CoA for fatty acid synthesis. PC participates in gluconeogenesis. MCC catalyzes a step in leucine metabolism. PCC catalyzes a step in the metabolism of propionyl-CoA. [1] [3] [4] Metabolic degradation of the biotinylated carboxylases leads to the formation of biocytin. This compound is further degraded by biotinidase to release biotin, which is then reutilized by holocarboxylase synthetase. [4]
Biotinylation of histone proteins in nuclear chromatin is a posttranslational modification that plays a role in chromatin stability and gene expression. [4] [8]
Primary biotin deficiency, meaning deficiency as a consequence of too little biotin in the diet, is rare, because biotin is contained in so many foods. Subclinical deficiency can cause mild symptoms, such as hair thinning, brittle fingernails, or skin rash, typically on the face. [2] [4]
Aside from inadequate dietary intake (rare), deficiency of biotin can be caused by a genetic disorder that affects biotin metabolism. The most common among these is biotinidase deficiency. Low activity of this enzyme causes a failure to recycle biotin from biocytin. Rarer are carboxylase and biotin transporter deficiences. [4] [26] Neonatal screening for biotinidase deficiency started in the United States in 1984, with many countries now also testing for this genetic disorder at birth. Treatment is lifelong dietary supplement with biotin. [1] If biotinidase deficiency goes untreated, it can be fatal. [27]
Low serum and urine biotin are not sensitive indicators of inadequate biotin intake. [4] However, serum testing can be useful for confirmation of consumption of biotin-containing dietary supplements, and whether a period of refraining from supplement use is long enough to eliminate the potential for interfering with drug tests. [28] [29] Indirect measures depend on the biotin requirement for carboxylases. 3-Methylcrotonyl-CoA is an intermediate step in the catabolism of the amino acid leucine. In the absence of biotin, the pathway diverts to 3-hydroxyisovaleric acid. Urinary excretion of this compound is an early and sensitive indicator of biotin deficiency. [2] [4]
Biotinidase deficiency is a deficiency of the enzyme that recycles biotin, the consequence of an inherited genetic mutation. [1] Biotinidase catalyzes the cleavage of biotin from biocytin and biotinyl-peptides (the proteolytic degradation products of each holocarboxylase) and thereby recycles biotin. [2] It is also important in freeing biotin from dietary protein-bound biotin. [30] Neonatal screening for biotinidase deficiency started in the United States in 1984, [31] which as of 2017 was reported as required in more than 30 countries. [32]
Profound biotinidase deficiency, defined as less than 10% of normal serum enzyme activity, which has been reported as 7.1 nmol/min/mL, has an incidence of 1 in 40,000 to 1 in 60,000, but with rates as high as 1 in 10,000 in countries with high incidence of consanguineous marriages (second cousin or closer). Partial biotinidase deficiency is defined as 10% to 30% of normal serum activity. [31] Incidence data stems from government mandated newborn screening. [32] For profound deficiency, treatment is oral dosing with 5 to 20 mg per day. Seizures are reported as resolving in hours to days, with other symptoms resolving within weeks. [31] Treatment of partial biotinidase deficiency is also recommended even though some untreated people never manifest symptoms. [31] Lifelong treatment with supplemental biotin is recommended for both profound and partial biotinidase deficiency. [1]
Inherited metabolic disorders characterized by deficient activities of biotin-dependent carboxylases are termed multiple carboxylase deficiency. These include deficiencies in the enzymes holocarboxylase synthetase. [1] Holocarboxylase synthetase deficiency prevents the body's cells from using biotin effectively and thus interferes with multiple carboxylase reactions. [30] There can also be a genetic defect affecting the sodium-dependent multivitamin transporter protein. [26]
Biochemical and clinical manifestations of any of these metabolic disorders can include ketolactic acidosis, organic aciduria, hyperammonemia, rash, hypotonia, seizures, developmental delay, alopecia and coma. [4]
Chemically modified versions of biotin are widely used throughout the biotechnology industry to isolate proteins and non-protein compounds for biochemical assays. [33] Because egg-derived avidin binds strongly to biotin with a dissociation constant Kd ≈ 10−15 M, [34] biotinylated compounds of interest can be isolated from a sample by exploiting this highly stable interaction. First, the chemically modified biotin reagents are bound to the targeted compounds in a solution via a process called biotinylation. The choice of which chemical modification to use is responsible for the biotin reagent binding to a specific protein. [33] Second, the sample is incubated with avidin bound to beads, then rinsed, removing all unbound proteins, while leaving only the biotinylated protein bound to avidin. Last, the biotinylated protein can be eluted from the beads with excess free biotin. [35] The process can also utilize bacteria-derived streptavidin bound to beads, but because it has a higher dissociation constant than avidin, very harsh conditions are needed to elute the biotinylated protein from the beads, which often will denature the protein of interest. [34]
When people are ingesting high levels of biotin in dietary supplements, a consequence can be clinically significant interference with diagnostic blood tests that use biotin-streptavidin technology. This methodology is commonly used to measure levels of hormones such as thyroid hormones, and other analytes such as 25-hydroxyvitamin D. Biotin interference can produce both falsely normal and falsely abnormal results. [1] [36] In the US, biotin as a non-prescription dietary supplement is sold in amounts of 1 to 10 mg per serving, with claims for supporting hair and nail health, and as 300 mg per day as a possibly effective treatment for multiple sclerosis [37] [38] (see § Research). Overconsumption of 5 mg/day or higher causes elevated concentration in plasma that interferes with biotin-streptavidin immunoassays in an unpredictable manner. [28] [29] Healthcare professionals are advised to instruct patients to stop taking biotin supplements for 48 h or even up to weeks before the test, depending on the specific test, dose, and frequency of biotin uptake. [28] Guidance for laboratory staff is proposed to detect and manage biotin interference. [29]
In 1916, W. G. Bateman observed that a diet high in raw egg whites caused toxic symptoms in dogs, cats, rabbits, and humans. [39] By 1927, scientists such as Margarete Boas and Helen Parsons had performed experiments demonstrating the symptoms associated with "egg-white injury." They had found that rats fed large amounts of egg-white as their only protein source exhibited neurological dysfunction, hair loss, dermatitis, and eventually, death. [40] [41]
In 1936, Fritz Kögl and Benno Tönnis documented isolating a yeast growth factor in a journal article titled "Darstellung von krystallisiertem biotin aus eigelb." (Representation of crystallized biotin from egg yolk). [42] The name biotin derives from the Greek word bios ('to live') and the suffix "-in" (a general chemical suffix used in organic chemistry). [5] Other research groups, working independently, had isolated the same compound under different names. Hungarian scientist Paul Gyorgy began investigating the factor responsible for egg-white injury in 1933 and in 1939, was successful identifying what he called "Vitamin H" (the H represents Haar und Haut, German for 'hair and skin'). [43] [44] Further chemical characterization of vitamin H revealed that it was water-soluble and present in high amounts in the liver. [45] After experiments performed with yeast and Rhizobium trifolii, West and Wilson isolated a compound they called co-enzyme R. [46] [47] By 1940, it was recognized that all three compounds were identical and were collectively given the name: biotin. [48] Gyorgy continued his work on biotin and in 1941 published a paper demonstrating that egg-white injury was caused by the binding of biotin by avidin. [49] [50] Unlike for many vitamins, there is insufficient information to establish a recommended dietary allowance, so dietary guidelines identify an "adequate intake" based on best available science with the understanding that at some later date this will be replaced by more exact information. [2] [9] [10]
Using E. coli, a biosynthesis pathway was proposed by Rolfe and Eisenberg in 1968. The initial step was described as a condensation of pimelyl-CoA and alanine to form 7-oxo-8-aminopelargonic acid. From there, they described three-step process, the last being introducing a sulfur atom to form the tetrahydrothiophene ring. [51]
High-dose biotin (300 mg/day = 10,000 times adequate intake) has been used in clinical trials for treatment of multiple sclerosis, a demyelinating autoimmune disease. [37] [38] The hypothesis is that biotin may promote remyelination of the myelin sheath of nerve cells, slowing or even reversing neurodegeneration. The proposed mechanisms are that biotin activates acetyl-coA carboxylase, which is a key rate-limiting enzyme during the synthesis of myelin, and by reducing axonal hypoxia through enhanced energy production. [37] [38] Clinical trial results are mixed; a 2019 review concluded that a further investigation of the association between multiple sclerosis symptoms and biotin should be undertaken, [37] whereas two 2020 reviews of a larger number of clinical trials reported no consistent evidence for benefits, [52] and some evidence for increased disease activity and higher risk of relapse. [53]
In the United States, biotin is promoted as a dietary supplement for strengthening hair and fingernails, though scientific data supporting these outcomes in humans are very weak. [3] [54] [55] A review of the fingernails literature reported brittle nail improvement as evidence from two pre-1990 clinical trials that had administered an oral dietary supplement of 2.5 mg/day for several months, without a placebo control comparison group. There is no more recent clinical trial literature. [54] A review of biotin as treatment for hair loss identified case studies of infants and young children with genetic defect biotin deficiency having improved hair growth after supplementation, but went on to report that "there have been no randomized, controlled trials to prove efficacy of supplementation with biotin in normal, healthy individuals." [55] Biotin is also incorporated into topical hair and skin products with similar claims. [56]
The Dietary Supplement Health and Education Act of 1994 states that the US Food and Drug Administration must allow on the product label what are described as "Structure:Function" (S:F) health claims that ingredient(s) are essential for health. For example: Biotin helps maintain healthy skin, hair and nails. If a S:F claim is made, the label must include the disclaimer "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease." [57]
In cattle, biotin is necessary for hoof health. Lameness due to hoof problems is common, with herd prevalence estimated at 10 to 35%. [58] Consequences of lameness include less food consumption, lower milk production, and increased veterinary treatment costs. Results after 4–6 months from supplementing biotin at 20 mg/day into daily diet reduces the risk of lameness. [58] [59] A review of controlled trials reported that supplementation at 20 mg/day increased milk yield by 4.8%. The discussion speculated that this could be an indirect consequence of improved hoof health or a direct effect on milk production. [60]
For horses, conditions such as chronic laminitis, cracked hooves, or dry, brittle feet incapable of holding shoes are a common problem. Biotin is a popular nutritional supplement. There are recommendations that horses need 15 to 25 mg/day. Studies report biotin improves the growth of new hoof horn rather than improving the status of existing hoof, so months of supplementation are needed for the hoof wall to be completely replaced. [61]
Riboflavin, also known as vitamin B2, is a vitamin found in food and sold as a dietary supplement. It is essential to the formation of two major coenzymes, flavin mononucleotide and flavin adenine dinucleotide. These coenzymes are involved in energy metabolism, cellular respiration, and antibody production, as well as normal growth and development. The coenzymes are also required for the metabolism of niacin, vitamin B6, and folate. Riboflavin is prescribed to treat corneal thinning, and taken orally, may reduce the incidence of migraine headaches in adults.
Vitamin C is a water-soluble vitamin found in citrus and other fruits, berries and vegetables. It is also a generic prescription medication and in some countries is sold as a non-prescription dietary supplement. As a therapy, it is used to prevent and treat scurvy, a disease caused by vitamin C deficiency.
Vitamins are organic molecules that are essential to an organism in small quantities for proper metabolic function. Essential nutrients cannot be synthesized in the organism in sufficient quantities for survival, and therefore must be obtained through the diet. For example, vitamin C can be synthesized by some species but not by others; it is not considered a vitamin in the first instance but is in the second. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, there are eight vitamers of vitamin E: four tocopherols and four tocotrienols.
Vitamin K is a family of structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation or for controlling binding of calcium in bones and other tissues. The complete synthesis involves final modification of these so-called "Gla proteins" by the enzyme gamma-glutamyl carboxylase that uses vitamin K as a cofactor.
Pantothenic acid (vitamin B5) is a B vitamin and an essential nutrient. All animals need pantothenic acid in order to synthesize coenzyme A (CoA), which is essential for cellular energy production and for the synthesis and degradation of proteins, carbohydrates, and fats.
Vitamin B6 is one of the B vitamins, and thus an essential nutrient. The term refers to a group of six chemically similar compounds, i.e., "vitamers", which can be interconverted in biological systems. Its active form, pyridoxal 5′-phosphate, serves as a coenzyme in more than 140 enzyme reactions in amino acid, glucose, and lipid metabolism.
Vitamin A is a fat-soluble vitamin that is an essential nutrient. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinyl esters, and several provitamin (precursor) carotenoids, most notably beta-carotene. Vitamin A has multiple functions: essential in embryo development for growth, maintaining the immune system, and healthy vision, where it combines with the protein opsin to form rhodopsin – the light-absorbing molecule necessary for both low-light and color vision.
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and storage. Folate is required for the body to make DNA and RNA and metabolise amino acids necessary for cell division and maturation of blood cells. As the human body cannot make folate, it is required in the diet, making it an essential nutrient. It occurs naturally in many foods. The recommended adult daily intake of folate in the U.S. is 400 micrograms from foods or dietary supplements.
Vitamin deficiency is the condition of a long-term lack of a vitamin. When caused by not enough vitamin intake it is classified as a primary deficiency, whereas when due to an underlying disorder such as malabsorption it is called a secondary deficiency. An underlying disorder can have 2 main causes:
B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. They are a chemically diverse class of compounds.
Streptavidin is a 52 kDa protein (tetramer) purified from the bacterium Streptomyces avidinii. Streptavidin homo-tetramers have an extraordinarily high affinity for biotin. With a dissociation constant (Kd) on the order of ≈10−14 mol/L, the binding of biotin to streptavidin is one of the strongest non-covalent interactions known in nature. Streptavidin is used extensively in molecular biology and bionanotechnology due to the streptavidin-biotin complex's resistance to organic solvents, denaturants, detergents, proteolytic enzymes, and extremes of temperature and pH.
Avidin is a tetrameric biotin-binding protein produced in the oviducts of birds, reptiles and amphibians and deposited in the whites of their eggs. Dimeric members of the avidin family are also found in some bacteria. In chicken egg white, avidin makes up approximately 0.05% of total protein (approximately 1800 μg per egg). The tetrameric protein contains four identical subunits (homotetramer), each of which can bind to biotin (Vitamin B7, vitamin H) with a high degree of affinity and specificity. The dissociation constant of the avidin-biotin complex is measured to be KD ≈ 10−15 M, making it one of the strongest known non-covalent bonds.
Biotinidase deficiency is an autosomal recessive metabolic disorder in which biotin is not released from proteins in the diet during digestion or from normal protein turnover in the cell. This situation results in biotin deficiency.
3-Methylcrotonyl-CoA carboxylase deficiency also known as 3-Methylcrotonylglycinuria is an inborn error of leucine metabolism and is inherited through an autosomal recessive fashion. 3-Methylcrotonyl-CoA carboxylase deficiency is caused by mutations in the MCCC1 gene, formerly known as MMCA, or the MCCC2 gene, formerly known as MCCB. MCCC1 encodes the a-subunits of 3-methylcrotonyl-CoA carboxylase while MCCC2 encodes the b-subunits. The clinical presentation of 3-Methylcrotonyl-CoA carboxylase deficiency is varied, even within members of the same family.
Biotinidase, also known as biotinase, is an enzyme that in humans is encoded by the BTD gene.
Biotin deficiency is a nutritional disorder which can become serious, even fatal, if allowed to progress untreated. It can occur in people of any age, ancestry, or of either sex. Biotin is part of the B vitamin family. Biotin deficiency rarely occurs among healthy people because the daily requirement of biotin is low, many foods provide adequate amounts of it, intestinal bacteria synthesize small amounts of it, and the body effectively scavenges and recycles it in the kidneys during production of urine.
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, and in both fatty acid and amino acid metabolism. It is important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the circulatory system in the maturation of red blood cells in the bone marrow. Plants do not need cobalamin and carry out the reactions with enzymes that are not dependent on it.
Antinutrients are natural or synthetic compounds that interfere with the absorption of nutrients. Nutrition studies focus on antinutrients commonly found in food sources and beverages. Antinutrients may take the form of drugs, chemicals that naturally occur in food sources, proteins, or overconsumption of nutrients themselves. Antinutrients may act by binding to vitamins and minerals, preventing their uptake, or inhibiting enzymes.
Relatively speaking, the brain consumes an immense amount of energy in comparison to the rest of the body. The mechanisms involved in the transfer of energy from foods to neurons are likely to be fundamental to the control of brain function. Human bodily processes, including the brain, all require both macronutrients, as well as micronutrients.
Selenium is an essential micronutrient for animals, though it is toxic in large doses. In plants, it sometimes occurs in toxic amounts as forage, e.g. locoweed. Selenium is a component of the amino acids selenocysteine and selenomethionine. In humans, selenium is a trace element nutrient that functions as cofactor for glutathione peroxidases and certain forms of thioredoxin reductase. Selenium-containing proteins are produced from inorganic selenium via the intermediacy of selenophosphate (PSeO33−).
{{cite journal}}
: CS1 maint: DOI inactive as of January 2024 (link)