Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calciummagnesiumand phosphatevitamin a and temperature, and multiple other biological effects. The major natural source of the vitamin is synthesis of cholecalciferol in the skin from cholesterol through a chemical reaction that is dependent on sun exposure specifically UVB radiation. Vitamin D from the diet or skin synthesis is biologically inactive; enzymatic conversion hydroxylation in the liver and kidney is required for activation.
As vitamin D can be synthesized in adequate amounts by most mammals exposed to sufficient sunlight, it is not an essential dietary factor, and so not technically a vitamin. Calcitriol also has other effects, vitamin a and temperature, including some on cell growth, neuromuscular and immune functions, and reduction of inflammation.
Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in children with rickets the childhood form of osteomalacia. Several forms vitamers of vitamin D exist. The two major forms are vitamin D 2 or ergocalciferol, and vitamin D 3 or cholecalciferol; vitamin D without a subscript refers to either D 2 or D 3 or both.
These are known collectively as calciferol. Inthe chemical structure of vitamin a and temperature D 3 was established and proven to result from the ultraviolet irradiation of 7-dehydrocholesterol. Chemically, the various forms of vitamin D are secosteroidsi. The active vitamin D metabolite calcitriol mediates its biological effects by binding to the vitamin D receptor VDRwhich is principally located in the nuclei of target cells.
VDR activation in the intestine, bone, kidney, and parathyroid gland cells leads to the maintenance of calcium and phosphorus levels in the blood with the assistance of parathyroid hormone and vitamin a and temperature and to the maintenance of bone content. One of the most important roles of vitamin D is to maintain skeletal calcium balance by promoting calcium absorption in the intestines, promoting bone resorption by increasing osteoclast number, maintaining calcium and phosphate levels for bone formationand allowing proper functioning of parathyroid hormone to maintain serum calcium levels, vitamin a and temperature.
Vitamin D deficiency can result in lower bone mineral density and an increased risk of reduced bone density osteoporosis or bone fracture because a lack of vitamin D alters mineral metabolism in the body. The VDR regulates cell proliferation and differentiation.
Vitamin D also affects the immune system, and VDRs are expressed in several white blood cellsincluding monocytes and activated T and B cells. A diet deficient in vitamin D in conjunction with inadequate sun exposure causes osteomalacia or rickets when it occurs in childrenwhich is a softening of the bones. In the developed world, vitamin a and temperature, this is a rare disease. Ricketsa childhood disease, is characterized by impeded growth and soft, weak, deformed long bones that bend and bow under their weight as children start to walk.
This condition is characterized by bow legs,  which can be caused by calcium or phosphorus deficiency, as well as a lack of vitamin D; today, it is largely found in low-income countries in Africa, Asia, or the Middle East  and in those with genetic disorders such as pseudovitamin D deficiency rickets. Maternal vitamin D deficiency may cause overt bone disease from before birth and impairment of bone quality after birth. Although rickets and osteomalacia are now rare in Britain, outbreaks have happened in some immigrant communities in which osteomalacia sufferers included women with seemingly adequate daylight outdoor exposure wearing Western clothing.
Vitamin D deficiency remains the main cause of rickets among young infants in most countries, because breast milk is low in vitamin D and social customs and climatic conditions can prevent adequate sun exposure. In sunny countries such as Nigeria, South Africa, and Bangladesh, where rickets occurs among older toddlers and children, it has been attributed to low dietary calcium intakes, which are characteristic of cereal-based diets with limited access to dairy products.
Osteomalacia is a disease in adults that results from vitamin D deficiency. Characteristics of this disease are softening of the bones, leading to bending of the spine, bowing of the legs, proximal muscle weakness, bone fragility, and increased risk for fractures. Dark-skinned people living in temperate climates have been shown to have low vitamin D levels but the significance of this is not certain.
The effects of vitamin D supplementation on health are uncertain. A United Type ii and diabetes Institute of Medicine report states: Research on vitamin a and temperature D supplements, including large-scale clinical trials, is continuing.
Vitamin D 3 supplementation has been tentatively found to lead to a reduced risk of death in the elderly,   but the effect has not been deemed pronounced or certain enough to make taking supplements recommendable. In general, no good evidence supports the commonly held belief that vitamin D supplements can help prevent osteoporosis.
Because it found mounting evidence for a benefit to wellbutrin xl and insomnia blogs health, though it had not found good evidence of other benefits, the US Food and Drug Administration has vitamin a and temperature manufacturers to declare the amount of vitamin D on nutrition facts labelspersonality anti depressants "nutrients of public health significance", since May Vitamin D supplements have been widely marketed for their claimed anticancer properties.
Reviews have described the evidence as being "inconsistent, inconclusive as to causality, and insufficient to inform nutritional requirements"  and "not sufficiently robust to draw conclusions". Taking vitamin D supplements does not meaningfully reduce the risk of strokecerebrovascular diseasecardial infarctionor ischaemic heart disease. In general, vitamin D functions to activate the innate and dampen the adaptive immune systems. Although tentative data link low levels of vitamin D to asthmaevidence to support a beneficial effect on asthmatics from supplementation is inconclusive.
Diabetes -- A systematic review of concluded that the available studies show no evidence vitamin a and temperature vitamin D3 supplementation having an effect on glucose homeostasis or diabetes prevention. Depression -- Clinical trials of vitamin D supplementation for depressive symptoms have generally been of low quality and show no overall effect, although subgroup analysis showed supplementation for participants with clinically significant depressive symptoms or depressive disorder had a moderate effect.
However, lower vitamin D concentrations are also associated with recruitment plan and jcaho nutrition and vitamin a and temperature less time outdoors. Therefore, alternative explanations for the increase in cognitive impairment exist and hence a direct causal vitamin a and temperature between vitamin D levels and cognition could not be established, vitamin a and temperature.
Pregnancy -- Low levels of vitamin D in pregnancy are associated with gestational diabetespre-eclampsiaand small for gestational age infants. Weight loss -- Though hypothesized that vitamin D supplementation may be an effective treatment for obesity apart from calorie restrictionone systematic review found no association of vitamin a and temperature with body weight or fat mass.
European Food Safety Authority. US Food and Drug Administration. Other possible agencies with claim guidance: Various institutions have proposed different recommendations for the amount of daily intake of vitamin D.
These vary according to precise definition, age, pregnancy or lactation, and the extent assumptions are made regarding skin synthesis of vitamin D, vitamin a and temperature. The dietary reference intake for vitamin D issued in by the Institute of Medicine IOM for North America superseded previous recommendations which gave adequate intake values.
The recommendations were formed assuming the individual has no skin synthesis of vitamin D because of inadequate sun exposure. The reference intake for vitamin D refers to total intake from food, beverages and supplements, and assumes that calcium requirements are being met. The tolerable upper intake level UL is defined as "the highest average daily intake of a nutrient that is likely to pose no risk of adverse health effects for nearly all persons in the general population, vitamin a and temperature.
Health Canada published recommended dietary allowances RDA and tolerable upper intake levels for vitamin D in  based on the Institute of Medicine report. Australia and New Zealand published nutrient reference values including guidelines for dietary vitamin D intake in The European Food Safety Authority EFSA in  reviewed the current evidence, finding the relationship between serum 25 OH D concentration and musculoskeletal health outcomes is widely variable.
The UK National Health Service recommends babies and young children aged six months to five years, pregnant or breastfeeding women, and sun-deprived elderly people should take daily vitamin supplements antibacterial plastic sheet ensure sufficient vitamin D intake.
Non-government organisations in Europe have made their own recommendations. Although vitamin D is not present naturally in most foods,   it is commonly added as a fortification in manufactured foods. In some countries, staple foods are artificially fortified with vitamin D.
In general, vitamin D 2 is found in fungi and vitamin D 3 is found in animals. The vitamin D 2 content in mushrooms and Cladina arbusculaa lichen, increase with exposure to ultraviolet light.
Manufactured foods fortified with Vitamin D include some fruit vitamin a and temperature and fruit juice drinks, meal replacement energy barssoy protein -based beverages, certain cheese and cheese products, flour products, infant formulasmany breakfast cereals relief of neck and shoulder pain, and milk. While some studies have found that vitamin D 3 raises 25 OH D blood levels faster and remains active in the body longer,   vitamin a and temperature contend that vitamin D 2 sources are equally bioavailable and effective as D 3 for raising and sustaining 25 OH D.
Vitamin D content in typical foods is reduced variably by cooking. Recommendations on recommended 25 OH D serum levels vary across authorities, and vary based on factors like age. No contributions to serum 25 OH D level are assumed from sun exposure and the recommendations are fully applicable to people with dark skin or negligible exposure to sunlight.
Vitamin D toxicity is rare. Pregnant or breastfeeding women should consult a doctor before taking a vitamin D supplement. In addition, for products intended for infants, the FDA recommends the dropper hold no more than IU.
One thousand micrograms per day in infants has produced toxicity within one month. Calcitriol itself is auto-regulated in a negative feedback cycle, and is also affected by parathyroid hormonefibroblast growth factor 23cytokinescalcium, and phosphate.
Vitamin D overdose causes hypercalcemia, which is vitamin a and temperature strong indication of vitamin D toxicity — this can be noted with an increase in urination and thirst. If hypercalcemia is not treated, it results in excess deposits of calcium in vitamin a and temperature tissues and organs such as the kidneys, liver, and heart, resulting in pain and organ damage.
The main symptoms of vitamin D overdose which are those of hypercalcemia including anorexianausea, and vomiting. These may be followed by polyuriapolydipsiaweakness, insomnia, nervousness, pruritus and ultimately renal failure. Furthermore, proteinuriaurinary castsazotemiaand metastatic calcification especially in the kidneys may develop. Vitamin D toxicity is treated by discontinuing vitamin D supplementation and restricting calcium intake. Kidney damage may be irreversible.
Exposure to sunlight for extended periods of time does not normally cause vitamin D toxicity. The concentrations of vitamin D precursors produced in the skin reach an equilibriumand any further vitamin D produced is degraded. Synthesis of vitamin D in nature is dependent on the presence of UV radiation and subsequent activation in liver and in kidney. Many animals synthesize vitamin D 3 from 7-dehydrocholesteroland many fungi synthesize vitamin D 2 from ergosterol.
Click on icon in lower right corner to open. Click on genes, proteins and metabolites below to link to respective articles, vitamin a and temperature. The transformation that converts 7-dehydrocholesterol to vitamin D 3 occurs in two steps. The process is faster in white button mushrooms. Vitamin D vitamin a and temperature is produced photochemically from 7-dehydrocholesterol in the skin of most vertebrate animals, including humans. Exposure to light through windows is insufficient because glass almost completely blocks UVB light.
The darker the skin, vitamin a and temperature, and the weaker the sunlight, the more minutes of exposure are needed. Vitamin D overdose is impossible from UV exposure; the skin reaches an equilibrium where the vitamin degrades as fast as it is created. Sunscreen absorbs or reflects ultraviolet light and prevents much vitamin a and temperature it from reaching the skin. The skin consists of two primary layers: Vitamin D is produced in the keratinocytes  of two innermost strata, the stratum basale and stratum spinosum.
Vitamin D can be synthesized only by a photochemical process. Phytoplankton in the ocean such as coccolithophore and Emiliania huxleyi have been photosynthesizing vitamin D for more than million years.