Vitamin D in health and disease: Current perspectives
Roel Jan A. Austral
ABSTRACT Despite the numerous reports of the association of vitamin D with a spectrum of development, disease treatment and health maintenance, vitamin D deficiency is common. Originating in part from the diet but with a key source resulting from transformation by exposure to sunshine, a great deal of the population suffers from vitamin D deficiency. It is linked to the treatment and pathogenesis and/or progression of several disorders including cancer, hypertension, multiple sclerosis, rheumatoid arthritis, osteoporosis, muscle weakness and diabetes. This widespread deficiency of Vitamin D merits consideration of widespread policies including increasing awareness among the public and healthcare professionals.
Vitamin D is a group of fat-soluble prohormones which were identified after the discovery of the anti-rachitic effect of cod liver oil in the early part of the 20th century. The vitamin found in cod liver oil was designated "D" following Vitamin A, B and C, which had been discovered earlier. The two major biologically inert precursors of vitamin D are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Vitamin D3 is formed when 7-dehydrocholesterol in the skin is exposed to solar ultraviolet B (UVB, 290-320 nm), and then converted to previtamin D3. In a heat-dependent process, previtamin D3 is immediately converted to vitamin D. Excess UVB rays transform previtamin D3 into biologically inactive metabolites, tachysterol and lumisterol. Vitamin D2 is plant derived, produced exogenously by irradiation of ergosterol, and enters the circulation through diet.
Both vitamin D precursors resulting from exposure to the sunshine and the diet are converted to 25-hydroxyvitamin D [25(OH)D] (calcidiol) when they enter the liver. 25(OH)D is the major circulating form of vitamin D and is used to determine vitamin D status. In order to be biologically...