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quote:There are two types of vitamin A toxicity, one caused by taking too much vitamin A over a short period of time (acute form) and one that occurs when the excess of the vitamin is present over a longer period (chronic hypervitaminosis A).In an infant, the suddenly intake of too much vitamin A may cause a bulging fontanelle ("soft spot" on the head) and symptoms resembling those of a brain tumor. This group of symptoms is called "pseudotumor cerebri" and it includes a bulging fontanelle, papilledema (swelling of the optic disc), and double vision. Vomiting and drowsiness are common.The symptoms in adults are less specific. Headache, visual changes, and impaired consciousness suggestive of pseudotumor cerebri may occur. Other symptoms can include nausea, vomiting, dizziness, and blurry vision.Chronic vitamin A toxicity develops after taking excessive doses of the substance for extended periods. Bone pain and swelling of the bones is common, often associated with high levels of calcium in the blood. Other symptoms include hair loss, high cholesterol, liver damage, and vision problems. Symptoms are often subtle and may include fatigue, malaise, and nausea.In children, hypervitaminosis A can cause craniotabes (abnormal softening of the skull bones). Irritability, decreased appetite, itchy skin, and poor weight gain are common. There may be skin changes with seborrhea (extremely oily skin and hair) and cracking at the corners of the mouth.Increased intracranial pressure is seen in both acute and chronic forms.
quote:Compared to most drugs, whether they be over-the-counter or prescription, vitamin are very safe. However, too much of a good thing is possible, and this month we will review some common negative effects of ingesting excessive amounts. Fat Soluble VitaminsVitamin AVitamin A gets a lot of publicity, especially from those health practitioners who are "antimicronutrient." In most individuals, vitamin A is very easily tolerated with no problems. Some of the most common signs and symptoms of vitamin A toxicity, which usually fall under the condition of hypervitaminosis A, include fatigue; headaches; muscle, joint and bone pain; dry, flaking skin; alopecia; amenorrhea; gastrointestinal problems, including nausea and vomiting; pruritus; and weight loss. Other problems that vitamin A overdose can cause include hepatomegaly, splenomegaly, liver damage, and a condition known as pseudotumor cerebri.1,2,3,4 Some of these signs and symptoms have been seen in certain individuals with amounts as low as 50,000 IU per day for a period of 18 to 24 months.1,3Conversely, there are many practitioners who have utilized vitamin A for teenage acne with levels of 300,000 to 500,000 IU per day for up to five months with no side effects.5 There have also been studies where people have ingested 1,000,000 IU per day, for five years with no toxicity whatsoever.2Not surprisingly, vitamin C is important in the treatment of vitamin A toxicity.1 This author recommends that if you use high dose vitamin A therapy that liberal amounts of vitamin C are also employed (minimum of 1,500 mg per day).Beta CaroteneUnlike vitamin A, there are no documented causes of liver damage with high doses. Orange skin is a common side effect seen with people who either drink a lot of carrot juice or ingest a lot of beta carotene. There have been no studies indicating that the change in skin color is toxic. High doses of beta carotene can, in some individuals, decrease vitamin E levels.3Vitamin DThe most common effects of vitamin D fall into the hypervitaminosis D condition, which include constipation, nausea, vomiting, anorexia, hypertension, hypercalcemia and hypercalciuria, polyuria, and polydipsia.1,4 Although vitamin D is in the fat-soluble vitamin family, most nutritional biochemists will tell you that it is actually a prohormone and not a vitamin. Because man can synthesize vitamin D in the skin with a little sun exposure, normal, healthy patients need not consume any more than 400 IU per day in supplemental form. Many new and reformulated vitamin formulas contain vitamin D in amounts ranging from 50 to 200 IU. If your patient is on multivitamins containing less than 400 IU of vitamin D, you need not worry about deficiency, provided they are not osteoporotic or in the process of healing a fracture.Vitamin EVitamin E is a very safe nutrient. However, large doses should be taken carefully in those people suffering from rheumatic heart disease, diabetes, hypertension, or hypothyroidism.3 In a few susceptible individuals, ingestion of over 1,000 IU of vitamin E per day may cause immune suppression.6 In levels below 1,000 IU, vitamin E is known to enhance the immune system.6 Finally, one of the first signs and symptoms of excess vitamin E intake is fatigue.7 Again, problems with vitamin E are very rare, and it is the safest of the commonly ingested, fat-soluble vitamins.Vitamin KVitamin K toxicity is rare. It may interfere with the therapeutic effect of Coumadin.3 There are three types of vitamin K: vitamin K1, which is in foods; vitamin K2, which is made in the small intestine of the body; and vitamin K3, the synthetic form, called menadione. Studies have shown that the K3 or menadione form can be toxic. In fact, the FDA has banned this synthetic vitamin K from supplements.1 (Isn't it amazing that the government actually banned something synthetic?)
quote:DefinitionVitamin toxicity is a condition in which a person develops symptoms as side effects from taking massive doses of vitamins. Vitamins vary in the amounts that are required to cause toxicity and in the specific symptoms that result. Vitamin toxicity, which is also called hypervitaminosis or vitamin poisoning, is becoming more common in developed countries because of the popularity of vitamin supplements. Many people treat themselves for minor illnesses with large doses (megadoses) of vitamins.DescriptionOverviewVitamins are organic molecules in food that are needed in small amounts for growth, reproduction, and the maintenance of good health. Some vitamins can be dissolved in oil or melted fat. These fat-soluble vitamins include vitamin D, vitamin E, vitamin A (retinol), and vitamin K. Other vitamins can be dissolved in water. These water-soluble vitamins include folate (folic acid), vitamin B12, biotin, vitamin B6, niacin, thiamin, riboflavin, pantothenic acid, and vitamin C (ascorbic acid). Taking too much of any vitamin can produce a toxic effect. Vitamin A and vitamin D are the most likely to produce hypervitaminosis in large doses, while riboflavin, pantothenic acid, biotin, and vitamin C appear to be the least likely to cause problems.Vitamins in medical treatmentVitamin supplements are used for the treatment of various diseases or for reducing the risk of certain diseases. For example, moderate supplements of folic acid appear to reduce the risk for certain birth defects (neural tube defects), and possibly reduce the risk of cancer. Therapy for diseases brings with it the risk for irreversible vitamin toxicity only in the case of vitamin D. This vitamin is toxic at levels which are only moderately greater than the recommended dietary allowance (RDA). Niacin is commonly used as a drug for the treatment of heart disease. Niacin is far less toxic than vitamin D. Vitamin toxicity is not a risk with medically supervised therapy using any of the other vitamins.Vitamin megadosesWith the exception of folic acid supplements, the practice of taking vitamin supplements by healthy individuals has little or no relation to good health. Most adults in the United States can obtain enough vitamins by eating a well-balanced diet. It has, however, become increasingly common for people to take vitamins at levels far greater than the RDA. These high levels are sometimes called vitamin megadoses. Megadoses are harmless for most vitamins. But in the cases of a few of the vitamins-- specifically vitamin D, vitamin A, and vitamin B6-- megadoses can be harmful or fatal. Researchers have also started to look more closely at megadoses of vitamin C and of vitamin E, since indirect evidence suggests that these two vitamins may reduce the risks of cancer, heart disease, and aging. It is not yet clear whether megadoses of either of these vitamins has any influence on health. Some experts think that megadoses of vitamin C may protect people from cancer. On the other hand, other researchers have gathered indirect evidence that vitamin C megadoses may cause cancer.Causes and symptomsFat-soluble vitaminsVITAMIN DVitamin D and vitamin A are the most toxic of the fat-soluble vitamins. The symptoms of vitamin D toxicity are nausea, vomiting, pain in the joints, and loss of appetite. The patient may experience constipation alternating with diarrhea, or have tingling sensations in the mouth. The toxic dose of vitamin D depends on its frequency. In infants, a single dose of 15 mg or greater may be toxic, but it is also the case that daily doses of 1.0 mg over a prolonged period may be toxic. In adults, a daily dose of 1.0-2.0 mg of vitamin D is toxic when consumed for a prolonged period. A single dose of about 50 mg or greater is toxic for adults. The immediate effect of an overdose of vitamin D is abdominal cramps, nausea and vomiting. Toxic doses of vitamin D taken over a prolonged period of time result in irreversible deposits of calcium crystals in the soft tissues of the body that may damage the heart, lungs, and kidneys.VITAMIN AVitamin A toxicity can occur with long-term consumption of 20 mg of retinol or more per day. The symptoms of vitamin A overdosing include accumulation of water in the brain (hydrocephalus), vomiting, tiredness, constipation, bone pain, and severe headaches. The skin may acquire a rough and dry appearance, with hair loss and brittle nails. Vitamin A toxicity is a special issue during pregnancy. Expectant mothers who take 10 mg vitamin A or more on a daily basis may have an infant with birth defects. These birth defects include abnormalities of the face, nervous system, heart, and thymus gland. It is possible to take in toxic levels of vitamin A by eating large quantities of certain foods. For example, about 30 grams of beef liver, 500 grams of eggs, or 2,500 grams of mackerel would supply 10 mg of retinol. The livers of polar bears and other arctic animals may contain especially high levels of vitamin A.VITAMIN EMegadoses of vitamin E may produce headaches, tiredness, double vision, and diarrhea in humans. Studies with animals fed large doses of vitamin E have revealed that this vitamin may interfere with the absorption of other fat-soluble vitamins. The term absorption means the transfer of the vitamin from the gut into the bloodstream. Thus, large doses of vitamin E consumed over many weeks or months might result in deficiencies of vitamin D, vitamin A, and vitamin K.VITAMIN KProlonged consumption of megadoses of vitamin K (menadione) results in anemia, which is a reduced level of red blood cells in the bloodstream. When large doses of menadione are given to infants, they result in the deposit of pigments in the brain, nerve damage, the destruction of red blood cells (hemolysis), and death. A daily injection of 10 mg of menadione into an infant for three days can kill the child. This tragic fact was discovered during the early days of vitamin research, when newborn infants were injected with menadione to prevent a disease known as hemorrhagic disease of the newborn. Today a different form of vitamin K is used to protect infants against this disease.Water-soluble vitaminsFOLATEFolate occurs in various forms in food. There are over a dozen related forms of folate. The folate in oral vitamin supplements occurs in only one form, however--folic acid. Large doses of folic acid (20 grams/day) can result in eventual kidney damage. Folate is considered, however, to be relatively nontoxic, except in cases where folate supplementation can lead to pernicious anemia.VITAMIN B12Vitamin B12 is important in the treatment of pernicious anemia. Pernicious anemia is more common among middle-aged and older adults; it is usually detected in patients between the ages of 40 and 80. The disease affects about 0.1% of all persons in the general population in the United States, and about 3% of the elderly population. Pernicious anemia is treated with large doses of vitamin B12. Typically, 0.1 mg of the vitamin is injected each week until the symptoms of pernicious anemia disappear. The patient then takes oral doses of vitamin B12 for the rest of his or her life. Although vitamin B12 toxicity is not an issue for patients being treated for pernicious anemia, treatment of these patients with folic acid may cause problems. Specifically, pernicious anemia is often first detected because the patient feels weak or tired. If the anemia is not treated, the patient may suffer irreversible nerve damage. The problem with folic acid supplements is that the folic acid treatment prevents the anemia from developing, but allows the eventual nerve damage to occur.VITAMIN B6Vitamin B6 is clearly toxic at doses about 1000 times the RDA. Daily doses of 2-5 grams of one specific form of this vitamin can produce difficulty in walking and tingling sensations in the legs and soles of the feet. Continued megadoses of vitamin B6 result in further unsteadiness, difficulty in handling small objects, and numbness in the hands. When the high doses are stopped, recovery begins after two months. Complete recovery may take two to three years.VITAMIN CThe RDA for vitamin C in adults is 60 mg per day. Large doses of vitamin C are considered to be toxic in persons with a family history of or tendency to form kidney stones or gallbladder stones. Kidney and gallbladder stones usually consist of calcium oxalate. Oxalate occurs in high concentrations in foods such as cocoa, chocolate, rhubarb, and spinach. A fraction of the vitamin C in the body is normally broken down in the body to produce oxalate. A daily supplement of 3.0 grams of vitamin C has been found to double the level of oxalate that passes through the kidneys and is excreted into the urine.NIACINThe RDA for niacin is 15-19 mg per day in adults. Niacin comes in two forms, nicotinic acid and nicotinamide. Either form can satisfy the adult requirement for this vitamin. Nicotinic acid, however, is toxic at levels of 100 times the RDA. It can cause flushing of the skin, nausea, diarrhea, and liver damage. Flushing is an increase in blood passing through the veins in the skin, due to the dilation of arteries passing through deeper parts of the face or other parts of the body. In spite of the side effects, however, large doses of nicotinic acid are often used to lower blood cholesterol in order to prevent heart disease. Nicotinic acid results in a lowering of LDL-cholesterol ("bad cholesterol"), an increase in HDL-cholesterol ("good cholesterol"), and a decrease in plasma triglycerides. Treatment involves daily doses of 1.5-4.0 grams of nicotinic acid per day. Flushing of the skin occurs as a side effect when nicotinic acid therapy is started, but may disappear with continued therapy.DiagnosisThe diagnosis of vitamin toxicity is usually made on the basis of the patient's dietary or medical history. Questioning the patient about the use of vitamin supplements may shed light on some of his or her physical symptoms. With some vitamins, the doctor can confirm the diagnosis by ordering blood or urine tests for specific vitamins. When large amounts of the water-soluble vitamins are consumed, a large fraction of the vitamin is absorbed into the bloodstream and promptly excreted into the urine. The fat-soluble vitamins are more likely to be absorbed into the bloodstream and deposited in the fat and other tissues. In the cases of both water-soluble and fat-soluble vitamins, any vitamin not absorbed by the intestines is excreted in the feces. Megadoses of many of the vitamins produce diarrhea, because the non-absorbed nutrient draws water out of the body and into the gut, resulting in the loss of this water from the body.TreatmentIn all cases, treatment of vitamin toxicity requires discontinuing vitamin supplements. Vitamin D toxicity needs additional action to reduce the calcium levels in the bloodstream because it can cause abnormally high levels of plasma calcium (hypercalcemia). Severe hypercalcemia is a medical emergency and may be treated by infusing a solution of 0.9% sodium chloride into the patient's bloodstream. The infusion consists of two to three liters of salt water given over a period of one to two days.PrognosisThe prognosis for reversing vitamin toxicity is excellent for most patients. Side effects usually go away as soon as overdoses are stopped. The exceptions are severe vitamin D toxicity, severe vitamin A toxicity, and severe vitamin B6 toxicity. Too much vitamin D leads to deposits of calcium salts in the soft tissue of the body, which cannot be reversed. Birth defects due to vitamin A toxicity cannot be reversed. Damage to the nervous system caused by megadoses of vitamin B6 can be reversed, but complete reversal may require a recovery period of over a year.PreventionVitamin toxicity can be prevented by minimizing the use of vitamin supplements. If vitamin D supplements are being used on a doctor's orders, vitamin toxicity can be prevented by monitoring the levels of plasma calcium. The development of hypercalcemia with vitamin D treatment indicates that the patient is at risk for vitamin D toxicity.
quote:Vitamin A is an important fat-soluble vitamin. Its basic molecule is a retinol, or vitamin A alcohol. In Western countries, 70% of dietary vitamin A is preformed as all trans-retinol. After absorption, retinol is transported via chylomicrons to the liver, where it is either stored as retinol ester or re-exported into the plasma in combination with retinol-binding protein for delivery to tissue sites.Sources of vitamin A include external supplementation and synthesis within the body from plant carotenes. The best sources of preformed vitamin A are liver, milk, kidney, and fish oil. The carotene substrates necessary for the synthesis of vitamin A are mainly found in plants, principally carrots.The bioavailability of retinol generally is more than 80%, whereas the bioavailability and bioconversion of carotenes are lower. These may be affected by species, molecular linkage, amount of carotene, nutrition status, genetic factors, and other interactions. While in general the body absorbs retinoids and vitamin A very efficiently, it lacks the mechanisms to destroy excessive loads. Thus, the chances for toxicity exist unless intake is regulated carefully. Revision of earlier estimates of daily human requirements of vitamin A has been suggested; the suggestion is that estimates ought to be revised downwards. Concern exists about the teratogenicity of vitamin A.
quote:Vitamin A Toxicity Excessive intake of vitamin A may cause acute or chronic toxicity. Acute toxicity in children may result from taking large doses (> 100,000 µg or 300,000 IU); it manifests as increased intracranial pressure and vomiting, which may lead to death unless ingestion is discontinued. After discontinuation, recovery is spontaneous, with no residual damage; only two fatalities have been reported. Within a few hours of ingesting several million units of vitamin A in polar bear or seal liver, arctic explorers developed drowsiness, irritability, headache, and vomiting, with subsequent peeling of the skin. Megavitamin tablets containing vitamin A have occasionally induced acute toxicity when taken for a long time.Chronic toxicity in older children and adults usually develops after doses of > 33,000 µg (100,000 IU)/day have been taken for months. In infants who are given 6,000 to 20,000 µg (20,000 to 60,000 IU)/day of water-miscible vitamin A, evidence of toxicity may develop within a few weeks. Birth defects have been reported in the children of women receiving 13-cis-retinoic acid (isotretinoin) for skin conditions during pregnancy (see Drugs in Pregnancy in Ch. 249).Massive doses (50,000 to 120,000 µg or 150,000 to 350,000 IU) of vitamin A or its metabolites are given daily to persons with globular acne. Although the treatment is effective, it puts the patient at risk for vitamin A toxicity.Although carotene is metabolized in the body to vitamin A at a slow rate, excessive ingestion of carotene does not cause vitamin A toxicity but produces carotenemia (carotene blood levels > 250 µg/dL [> 4.65 µmol/L]). This condition is usually asymptomatic but may lead to carotenosis, in which the skin (but not the sclera) becomes deep yellow, especially on the palms and soles. Carotenosis may also occur in diabetes mellitus, myxedema, and anorexia nervosa, possibly from a further reduction in the rate of conversion of carotene to vitamin A.Symptoms, Signs, and Diagnosis Sparse coarse hair, alopecia of the eyebrows, dry rough skin, and cracked lips are early signs. Later, severe headache, pseudotumor cerebri, and generalized weakness are prominent. Cortical hyperostosis and arthralgia are common, especially in children. Hepatomegaly and splenomegaly may occur.Normal fasting plasma retinol levels range from 20 to 80 µg/dL (0.7 to 2.8 µmol/L). In vitamin A toxicity, fasting plasma levels may exceed 100 µg/dL (3.49 µmol/L), up to 2000 µg/dL (69.8 µmol/L). Differential diagnosis may be difficult because symptoms are varied and bizarre, but they usually include headache and rash.Prognosis and Treatment Prognosis is excellent for adults and children. Symptoms and signs usually disappear within 1 to 4 wk after stopping vitamin A ingestion. However, prognosis for the fetus of a mother taking megadoses of vitamin A is guarded.
quote:Originally posted by heikkiHi. Again.But my question is that, what is vitamin? How it looks like? What is one individual vitamin, form, weight, size, color, material construction, etc.
quote:The term vitamin D refers to the secosterols ergocalciferol or vitamin D2 and cholecalciferol or vitamin D3 as well as to the metabolites and analogues of these substances. All forms of vitamin D possess antirachitic activity. Vitamin D is different from all of the other vitamins in human nutrition because it is the only vitamin that is a conditional one. Vitamin D3 is synthesized in the skin from 7-dehydrocholesterol via photochemical reactions using ultraviolet B (UV-B) radiation from sunlight. However, there are conditions where the synthesis of vitamin D3 in the skin is not sufficient to meet physiological requirements. Humans who are not exposed to sufficient sunlight due to reason of geography, shelter or clothing, require dietary intake of vitamin D. Under these conditions, vitamin D is an essential nutrient. Vitamin D without a subscript refers to either vitamin D2 or vitamin D3.Vitamin D is the principal regulator of calcium homeostasis in the body. It is particularly important in skeletal development and bone mineralization. Vitamin D is a prohormone. That is, it has no hormone activity itself, but is converted to a molecule which does.The active form of vitamin D is 1alpha, 25-dihydroxyvitamin D or 1,25(OH2)D (again, when D is used without a subscript it refers to either D2 or D3). The vitamin D hormone 1,25 (OH2)D mediates its actions via binding to vitamin D receptors (VDRs) which are principally located in the nuclei of target cells. 1,25(OH2)D enhances the efficiency of calcium absorption, and, to a much lesser extent, phosphorus absorption, from the small intestine. Vitamin D deficiency is characterized by inadequate mineralization or demineralization of the skeleton. Inadequate mineralization of the skeleton is the cause of rickets in children (vitamin D is also known as the antirachitic factor), while demineralization of the skeleton results in osteomalcia in adults. Further, vitamin D deficiency in adults can lead to osteoporosis. This results from a compensatory increase in the production of parathyroid hormone resulting in resorption of bone.Very few foods are natural sources of vitamin D. Foods that do contain vitamin D include fatty fish, fish liver oils (e.g., cod liver oil) and eggs from hens that have been fed vitamin D. Nearly all the vitamin D intake from foods comes from fortified milk products and other foods, such as breakfast cereals, that have been fortified with vitamin D. Vitamin D is a fat-soluble vitamin and therefore its absorption is adversely affected in those with malabsorption disorders. Those with chronic liver disease, cystic fibrosis, Crohn's disease, Whipple's disease and sprue are prone to vitamin D deficiency. Others at risk for vitamin D deficiency, include those that do not drink milk and who do not receive much sunlight, those who live in regions where they receive little natural light and alcoholics. The elderly are at risk for vitamin D deficiency for several reasons, including inadequate exposure to sunlight, consumption of low amounts of vitamin D-containing foods and the use of certain drugs which interfere with the absorption and/or metabolism of vitamin D (see Interactions). The use of sunscreens may be another factor that may negatively affect vitamin D status.The two forms of vitamin D used for nutritional supplementation are the secosterols ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Secosterols or secosteroids are derived from the cyclopentanoperhydrophenanthrene ring structure, the basic structure of all steroids. The cyclopentanoperhydrophenanthrene structure is comprised of four rings (A, B, C and D). Secosterols or secosteroids are steroids in which one of the rings has been broken. In the case of vitamin D, the bond between carbons 9 and 10 of ring B is broken, and this is indicated by the inclusion of "9, 10-seco" in the chemical name of the molecule. Seco is from the Greek word for split.Vitamin D2 is derived from fungal and plant sources. Vitamin D2 is also known as ergocalciferol. Its chemical names are 9, 10-seco (5Z, 7E)-5, 7, 10(19), 22-ergostatetraene-3beta-ol and (3 beta, 5Z, 7E, 22E)-9, 10-secoergosta-5, 7, 10(19), 22-tetraen-3-ol. Its molecular formula is C28H44O and its molecular weight is 396.66 daltons. The configuration of the double bonds are notated E for entgegen (from the German, meaning to stand opposite to) or trans, and Z for zusammen (from the German, meaning together) or cis. Vitamin D2 is represented by the following structural formula:Vitamin D2Vitamin D3 is derived from animal sources. Vitamin D3 is also known as cholecalciferol and calciol. Its chemical names are 9, 10-seco (5Z, 7E)-5, 7, 10(19) cholestatriene-3beta-ol and (3beta, 5Z, 7E)-9, 10-secocholesta-5, 7, 10(19)-trien-3-ol. Its molecular formula is C27H44O, and its molecular weight is 384.65 daltons. The only structural difference between vitamin D2 and vitamin D3 is in their side chains. The side chain of vitamin D2 contains a double bond between carbons 22 and 23 and a methyl group on carbon 24. The structural formula of vitamin D3 can be represented as follows:Vitamin D3Pharmaceutical forms of vitamin D include calcitriol (1alpha, 25-dihydroxycholecalciferol), doxercalciferol and calcipotriene. Calcitriol and doxercalciferol are used to treat certain metabolic disorders; calcipotriene is used topically for the treatment of psoriasis.Vitamin D analogues called deltanoids are being developed as chemopreventive agents. These analogues separate desirable antiproliferative and pro-differentiation activities from the undesirable hypercalcemic activity of vitamin D. High doses of vitamin D can result in hypercalcemia.
quote:ascorbic acid (vitamin C), C6H8O6;
quote:Many different geometric isomers of retinol, retinal and retinoic acid are possible as a result of either a trans or cis configuration of the four double bonds found in the polyene chain. The cis isomers are less stable and can readily convert to the all-trans configuration (as seen in the structure of all-trans-retinol shown here). Nevertheless, some cis isomers are found naturally and carry out essential functions. For example, the 11-cis-retinal isomer is the chromophore of rhodopsin, the vertebrate photoreceptor molecule. Rhodopsin is comprised of the 11-cis-retinal covalently linked via a Schiff base to the opsin protein (either rod opsin or blue, red or green cone opsins). The process of vision relies on the light-induced isomerisation of the chromophore from 11-cis to all-trans resulting in a change of the conformation and activation of the photoreceptor molecule. One of the earliest signs of vitamin A deficiency is night-blindness followed by decreased visual acuity.As can be seen from the structure, retinol is derived from isoprene, and has an alcohol functional group. The first full synthesis route for the compound was found by David Adriaan van Dorp and Jozef Ferdinand Arens in 1947.George Wald won the 1967 Nobel Prize in Physiology or Medicine for his work with retina pigments (also called visual pigments), which led to the understanding of the role of vitamin A in vision.Many of the non-visual functions of vitamin A are mediated by retinoic acid, which regulates gene expression by activating intracellular retinoic acid receptors. The non-visual functions of vitamin A are essential in the immunological function, reproduction and embryonic development of vertebrates as evidenced by the impaired growth, susceptibility to infection and birth defects observed in populations receiving suboptimal vitamin A in their diet.Retinol can also be used in the treatment of acne in a topical cream. A form of retinoic acid, all-trans retinoic acid (ATRA) is currently used as chemotherapy for acute promyelocytic leukemia, a subtype of acute myelogenous leukemia. This is because this transformed cells of this subtype respond in most cases to agonists of the retinoic acid receptor (RAR).
quote:Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. Vitamin E is often used in skin creams and lotions because it is believed to play a role in encouraging skin healing and reducing scarring after injuries such as burns.Natural vitamin E exists in eight different forms or isomers, four tocopherols and four tocotrienols. All isomers have a chromanol ring, with a hydroxyl group which can donate a hydrogen atom to reduce free radicals and a hydrophobic side chain which allows for penetration into biological membranes. There is an alpha, beta, gamma and delta form of both the tocopherols and tocotrienols, determined by the number of methyl groups on the chromanol ring. Each form has its own biological activity, the measure of potency or functional use in the body.
quote:Depression and anxiety disorders are serious medical illnesses that affect around 50 million American adults. Everyone has times when they're feeling down. For people with the medical condition called depression, feeling very sad or having no interest in activities can last for a long time. Sometimes this happens to people for no obvious reason, even when their lives are going well. Anxiety disorders can fill people's lives with overwhelming anxiety symptoms and fear. Unlike the slight anxiety caused by a stressful event, like a business presentation or a first date, anxiety disorders are constant and can grow worse with time if not treated. Each anxiety disorder has its own specific symptoms, but what they all have in common is intense, irrational fear and dread.
do we actually need vitamin supplements? you see in boots for instance, a whole range of suppliments with a lot aimed at children.do children need supplements?I can see a case for them in more deprived countries where a balanced diet may not be possible.