Vitamin D is a group of fat-soluble secosteroids, the two major physiologically relevant forms of which are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D can be synthesized by the body from cholesterol when sun exposure is adequate (when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis). Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation.
Vitamin D promotes calcium absorption in the intestine and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of the bones and to prevent hypocalcemic tetany. It is also needed for bone growth and remodeling. Vitamin D is important for the modulation of cell growth, neuromuscular and immune functions, as well as for the reduction of inflammation. It may reduce the risk of developing multiple sclerosis, asthma, cancer as well as rheumatoid arthritis in women. Low levels of vitamin D may increase the risk of heart attack and early death. Hypovitaminosis D is known to cause several bone diseases, such as rickets in children (impeded growth, and deformity of the long bones), osteomalacia (a bone-thinning disorder), osteoporosis (reduced bone mineral density and increased bone fragility), as well as muscle aches and weakness.
Although there is no consensus on vitamin D levels required for optimal health (and it likely differs depending on age and health conditions), serum concentration of less than 20 ng/ml is generally considered inadequate, requiring treatment. There are only a few foods that are good sources of vitamin D, so vitamin D supplements are often recommended unless you are exposed to sunlight on your skin regularly. Fish liver oils (such as cod liver oil), fatty fish species (catfish, salmon, mackerel, tuna, sardines), eggs (egg yolk) are among the best sources of vitamin D3. While choosing the best fish liver oil, one should pay attention to the proper doses of vitamin D and A. All the fat-soluble vitamins should be dosed carefully. Some mushrooms and lichens are good sources of vitamin D2.
- relevant [ˈrɛləvənt] – istotny, mający znaczenie
- adequate [ˈædɪkwɪt] – odpowiedni, stosowany, zadowalający, adekwatny
- to strike [tə straɪk] – uderzać, trafiać
- to trigger [tə ˈtrɪgər] – wywoływać
- inert [ɪnˈɜrt] – nieczynny chemicznie, nieaktywny
- to undergo [tə ʌndərˈgoʊ] – poddawać się, przechodzić, doświadczać
- tetany [ˈtɛtni] – tężyczka
- multiple sclerosis [ˈmʌltəpəl sklɪˈroʊsɪs] – stwardnienie rozsiane
- rickets [ˈrɪkɪts] – krzywica
- impeded [ɪmˈpidɪd] – zahamowany
- osteomalacia [ɒstioʊməˈleɪʃiə] – osteomalacja
- osteoporosis [ɒstioʊpəˈroʊsɪs] – osteoporoza
- cod liver oil [kɒd ˈlɪvər ɔɪl] – tran z dorsza
- catfish [ˈkætfɪʃ] – zębacz
- salmon [ˈsæmən] – łosoś
- mackerel [ˈmækərəl] – makrela
- tuna [ˈtunə] – tuńczyk
- sardine [sɑrˈdin] – sardynka
- yolk [yoʊlk] – żółtko
- lichen [ˈlaɪkən] – porost