Vitamin D | |
---|---|
Drug class | |
Class identifiers | |
Synonyms | Calciferols |
Use | Rickets, osteoporosis, osteomalacia, vitamin D deficiency |
ATC code | A11CC |
Biological target | vitamin D receptor |
Clinical data | |
Drugs.com | MedFacts Natural Products |
External links | |
MeSH | D014807 |
Legal status | |
In Wikidata |
Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, along with numerous other biological functions.[1][2] In humans, the most significant compounds within this group are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).[2][3]
The primary natural source of vitamin D is the synthesis of cholecalciferol in the lower layers of the skin’s epidermis, triggered by a photochemical reaction with ultraviolet B (UV-B) radiation from sunlight or UV-B lamps.[1] Cholecalciferol and ergocalciferol can also be obtained through diet and supplements.[1][2] Foods such as the flesh of fatty fish are good sources of vitamin D, though there are few other foods where it naturally appears in significant amounts.[2][4] In the U.S. and other countries, cow's milk and plant-based milk substitutes are fortified with vitamin D, as are many breakfast cereals.[1] Mushrooms exposed to ultraviolet light also provide useful amounts of vitamin D2.[2][5] Dietary recommendations typically assume that all of a person's vitamin D is taken by mouth, given the variability in sunlight exposure among the population and uncertainties regarding safe levels of sunlight exposure, particularly due to the associated risk of skin cancer.[2]
Vitamin D obtained from the diet or synthesised in the skin is biologically inactive. It becomes active by two enzymatic hydroxylation steps, the first occurring in the liver and the second in the kidneys.[1][3] Since most mammals can synthesise sufficient vitamin D with adequate sunlight exposure, it is technically not essential in the diet and thus not a true vitamin. Instead it functions as a hormone; the activation of the vitamin D pro-hormone produces calcitriol, the active form. Calcitriol then exerts its effects via the vitamin D receptor, a nuclear receptor found in various tissues throughout the body.[6]
Cholecalciferol is converted in the liver to calcifediol (also known as calcidiol or 25-hydroxycholecalciferol), while ergocalciferol is converted to ercalcidiol (25-hydroxyergocalciferol).[1] These two vitamin D metabolites, collectively referred to as 25-hydroxyvitamin D or 25(OH)D, are measured in serum to assess a person's vitamin D status.[7][8] Calcifediol is further hydroxylated by the kidneys and certain immune cells to form calcitriol (1,25-dihydroxycholecalciferol), the biologically active form of vitamin D.[9][10] Calcitriol circulates in the blood as a hormone, playing a major role in regulating calcium and phosphate concentrations, as well as promoting bone health and bone remodeling.[1] Additionally, calcitriol has other effects, including influencing cell differentiation, neuromuscular and immune functions, and reducing inflammation.[2]
Vitamin D has a significant role in calcium homeostasis and metabolism.[1] Its discovery was due to effort to identify the dietary deficiency in children with rickets, the childhood form of osteomalacia.[11] Vitamin D supplements are commonly used to treat or to prevent osteomalacia and rickets.[1] The evidence for other health benefits of vitamin D supplementation in individuals who are already vitamin D sufficient is inconsistent.[2] The effect of vitamin D supplementation on morbidity and mortality is also unclear, with one meta-analysis finding a small decrease in mortality in elderly people.[12] Except for the prevention of rickets and osteomalacia in high-risk groups, any benefit of vitamin D supplements to musculoskeletal or general health may be small and in some cases, may have adverse effects on health.[13][14][15]
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was invoked but never defined (see the help page).The authors conclude that there is therefore little reason to use vitamin D supplements to maintain or improve musculoskeletal health, except for the prevention of rare conditions such as rickets and osteomalacia in high risk groups, which can be caused by vitamin D deficiency after long lack of exposure to sunshine.