Vitamin D - importance of laboratory evaluation

Vitamin D is unique among vitamins, as it acts as a hormone and may be synthesized in the skin from exposure to sunlight. In addition to its effects on phosphorus-calcium metabolism, recent evidence correlates insufficient levels of vitamin D with an increased risk of developing other diseases, not bone related. Serum levels of 25-hydroxyvitamin D (25( OH)D) is the best indicator of vitamin D body content, as it reflects the vitamin obtained from dietary intake and exposure to sunlight, as well as the conversion of vitamin D from fatty deposits in liver. 25(OH)D levels form a continuous spectrum of vitamin D sufficiency. Although controversial, there appears to be a "consensus" that plasma levels of 25( OH)D below 30-32 ng/m1 indicates a relative deficiency of vitamin D. Vitamin D used for replacement occurs in two major forms: cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Both vitamins are equivalent, both increase serum levels of 25 (OH) D similarly, suggesting an equivalent absorption. The latest Endocrine Society guidelines suggest screening for vitamin D deficiency only in individuals at risk and not in the general population. In these patients, it is recommended the measurement of 25(OH)D circulating in serum, by a reliable analytical method. The vitamin D deficiency is defined by a value of 25 (OH) D less than 20 ng/m1 (50 nmo1/1). In individuals at risk, it is recommended the intake of dietary vitamin D, according to the age and special medical conditions (pregnancy, breastfeeding, obesity and concomitant intake of drugs). For treatment and prevention of vitamin D deficiency it is suggested the use of any of the isoforms (vitamin D2 or vitamin D3) in an age-dependent and individual dose. To obtain the non-calcemic benefits of vitamin D, the Endocrine Society recommends vitamin D supplementation to prevent its decrease. However, supplementation beyond the recommended daily dose is not recommended for the purpose of preventing cardiovascular death or increase quality of life. (C) 2012 Sociedade Portuguesa de Endocrinologia, Diabetes e Metabolismo. Published by Elsevier Espana, S.L. All rights reserved.