Rocz Panstw Zakl Hig. 2014;65(3):179-84.
Wranicz J1, Szostak-Węgierek D.
Julia Wranicz, Chair of Dietetics, Department of Nutritional Physiology, Faculty of Human Nutrition and Consumer Sciences, Warsaw University of Life Sciences – SGGW, Nowoursynowska street 159c, 02-776 Warsaw, Poland
|Adipose tissue||Skin tissue||Placenta|
|Osseous tissue||Hair follicle||Uterus|
|Smooth muscles||Fetal liver||Testicle|
|Fetal muscle tissue||Brain||Parotid gland|
|Adrenal gland||Parathyroid gland||Retina|
|Cancer cells||Pituitary gland||Bone marrow|
|Stomach||Thymus gland||Pancreatic beta-cells|
|Small intestine||Thyroid gland||Osteoblasts|
|Large intestine||Mammary gland||Lymphocytes B and T|
Vitamin D is a compound responsible for maintaining mineral homeostasis. It protects against calcium and phosphate deficiency through the effects on the intestine, kidney, parathyroid gland and bone. All mechanisms that help maintain mineral homeostasis of the body are regulated by the vitamin D hormonal form - calcitriol. Synthesis of vitamin D starts in the skin as a non-enzymatic process, which begins during exposure to sunlight, when the absorption of ultraviolet B (UVB) radiation results in convertion of 7-dehydrocholesterol, a metabolite of cholesterol that is stored in the skin, to precholecalciferol (previtamin-D₃) that is immediately converted into cholecalciferol (vitamin D₃). After the skin synthesis cholecalciferol is transported to the liver where it undergoes hydroxylation, what results in formation of calcidiol (25(OH)D₃). The second metabolic process takes place in the kidney, where calcidiol undergoes hydroxylation at the C-1 position to the hormonal, the most active metabolite - 1,25-dihydroxyvitamin D (calcitriol).
Vitamin D deficiency may result in bone diseases, such as rickets in children and osteomalacia and osteoporosis in adults. Symptoms of osteomalacia affect mainly the skeletal system and are similar to that observed in rickets. It concerns thoracic kyphosis, pelvis deformities and also the varus knee. Osteoporosis is another condition that is related to abnormalities of mineral homeostasis. It is characterized by the progressive loss of bone mass, impaired bone microarchitecture, and consequently increased fragility and susceptibility to fracture. For the last several years other, non-classic actions of vitamin D₃ have been discussed. It was engendered by the discovery of vitamin D3 receptor (VDR) in the most of body tissues and cells.
Hence, there are many hypotheses which suggest the inverse relationship between vitamin D status and various diseases, such as cancer, autoimmune diseases, diabetes mellitus and others.
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Wranicz J, Szostak-Węgierek D.
Apart from the classic role of vitamin D, its hormonal active form, calcitriol is also characterized by pleiotropic effects on various organs and tissues. For the last several years, many researchers have shown an association between deficiency of vitamin D and the risk of type 2 diabetes mellitus (T2DM). Recent investigations suggested the need of vitamin D supplementation in T2DM prevention. It was shown that vitamin D deficiency decreases insulin secretion. It was also observed that proper vitamin D supplementation may improve the ability of the cells of the islets of Langerhans to synthesize many proteins de novo and to convert proinsulin to insulin. Apart from regulating bone metabolism and also calcium and phosphate homeostasis, 1,25(OH)2D3 exerts antiproliferative and pro-differentiating effects on a wide variety of cell types. It also induces apoptosis of cancer cells and slows their proliferation. In a number of major studies the relationship between low vitamin D levels and increased risk of various cancers was observed. It concerns colorectal, lung, prostate, breast and ovarian cancer. It was observed that in patients with low serum vitamin D concentrations such disorders as ischemic heart disease, heart attack, stroke, cardiac arrhythmia, and hypertension were more frequent and mortality was significantly higher. These results led the researchers to consider vitamin D deficiency as a potential risk factor for cardiovascular diseases. The possible mechanism in the pathogenesis of cardiovascular diseases that may be related to low levels of vitamin D, is its adverse effect on the renin-angiotensin-aldosterone system (RAAS). Calcitriol is also an important determinant of muscle cell proliferation and differentiation, as well as inhibition of apoptosis. Vitamin D is synthesized in the skin. However, there are only a few food products that are rich in vitamin D3, e.g.: fish oils, fish and fortified-products, such as dairy products and margarines. Individuals who are vulnerable to vitamin D deficiency should be supplemented.
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