Vitamin D is a fat-soluble vitamin that is found in food and can also be made in your body after exposure to ultraviolet (UV) rays from the sun. The major biological function of vitamin D is to maintain normal blood levels of calcium and phosphorus by promoting their absorption from food in the intestines, and by promoting re-absorption of calcium in the kidneys. It promotes bone formation and mineralization and is essential in the development of an intact and strong skeleton. It inhibits parathyroid hormone secretion, which enhances the release of calcium from the large reservoir contained in the bones from the parathyroid gland.
Vitamin D deficiency is known to cause several bone disease. The most prevalent of which are rickets, osteomalacia and osteoporosis. Rickets is childhood disease characterized by impeded growth and deformity of the long bones. Osteomalacia is bone-thinning disorder that occurs exclusively in adults and is characterised by proximal muscle weakness and bone fragility. Osteoporosis is a condition characterized by reduced bone mineral density and increased bone fragility.
Vitamin D malnutrition may also be linked to an increased susceptibility to several chronic diseases such as high blood pressure, tuberculosis, cancer, periodontal disease, multiple sclerosis, chronic pain, depression, schizophrenia, seasonal affective disorder and several autoimmune diseases.
Very few foods naturally contain significant amounts of Vitamin D. Fortified foods represent the major dietary sources of vitamin D, such as fortified bread, margarine, breakfast cereals and milk. Natural vegetarian sources of vitamin D include mushrooms, eggs and yeast.
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