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Is vitamin D deficiency important in the natural history of COPD?
  1. J K Quint,
  2. J A Wedzicha
  1. Academic Unit of Respiratory Medicine, University College London, UK
  1. Correspondence to Dr JK Quint, University College London, Department of Academic Respiratory Medicine, Royal Free Hospital, Rowland Hill Street, London NW3 2QG, UK; j.quint{at}

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Vitamin D consists of a group of fat-soluble prohormones, the most important of which are vitamin D2 and D3, with measurement of 25-hydroxyvitamin D (25-OHD) closely representing a person's vitamin D2 and D3 status. D2 (ergocalciferol) is plant and fungal derived, while vitamin D3 (cholecalciferol) is made from 7-dehydrocholesterol in the skin. This conversion of 7-dehydrocholesterol to previtamin D3 is governed by both the intensity and appropriate wavelength of the ultraviolet (UV) B irradiation reaching 7-dehydrocholesterol. Adequate amounts of vitamin D3 can be made in the skin after only 10–15 min of sun exposure at least twice a week without sunscreen. However, with longer exposure to UVB rays, equilibrium is achieved in the skin and the vitamin degrades as fast as it is generated. Serum concentrations of vitamin D have been found to vary with age, race, sex, season and geographic location, and subclinical deficiency is common, particularly in temperate climates.1

Once in its physiologically active form vitamin D is released into the circulation, binds to a carrier protein in the plasma (vitamin D-binding protein (DBP)) and is transported to various target organs. The hormonally active form of vitamin D mediates its biological effects by binding to the vitamin D receptor (VDR), which is principally located in the nuclei of target cells. This VDR is constitutively expressed in monocytes, activated macrophages, dendritic cells, natural killer cells, and T and B cells. Activation has potent antiproliferative, prodifferentiative and immunomodulatory functions; both immune enhancing and immunosuppressive.2 It is these immunomodulatory properties of vitamin D that have particularly attracted interest in recent years with regards …

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