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The D-lemma: To Screen or Not to Screen for 25-Hydroxyvitamin D Concentrations

¹ Department of Medicine, Section of Endocrinology, Nutrition, and Diabetes, Vitamin D, Skin, and Bone Research Laboratory, Boston University Medical Center, Boston, MA.

^aAddress correspondence to the author at: Boston University School of Medicine, 715 Albany St., Boston, MA 02215. Fax 617-638-8882; e-mail mfholick@bu.edu.

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Until recently, there has been little interest in the medical and pediatric communities regarding the vitamin D status of their patients. It had been assumed that everyone was vitamin D sufficient and that only those patients with fat-malabsorption syndromes were at risk(1). African Americans were at risk because of their sunscreening skin pigment, but little attention was placed on their vitamin D status because African Americans were at less risk of fracture than Caucasians. The introduction of drugs to treat osteoporosis made physicians aware that vitamin D deficiency was a contributing factor for osteoporosis.

Vitamin D made in the skin or ingested from the diet is converted in the liver to 25-hydroxyvitamin D [25(OH)D]¹ (1)(2), the major circulating form of vitamin D used for evaluating the vitamin D status of patients. 25(OH)D is hydroxylated in the kidneys to form the biologically active metabolite 1,25-dihydroxyvitamin D [1,25(OH)₂D](1)(2). Because most children and adults were assumed to be vitamin D sufficient when reference intervals for 25(OH)D were determined, values ranged from 10 µg/L (ng/mL) to 55 µg/L. Studies of adults that evaluated parathyroid hormone (PTH) with 25(OH)D revealed, however, that PTH concentrations began to plateau at 30–40 µg/L(3). Healthy adults receiving vitamin D and calcium supplementation who had blood 25(OH)D concentrations between 11 µg/L and 19 µg/L demonstrated substantial decreases in their PTH concentrations, whereas adults with a 25(OH)D concentration between 20 µg/L and 25 µg/L had no significant change in PTH, suggesting that vitamin D deficiency should be defined as a 25(OH)D concentration <20 µg/L(4). Postmenopausal women whose 25(OH)D concentration increased from approximately 20 µg/L to approximately 32 µg/L had a 65% increase in intestinal calcium absorption(5). Thus, vitamin D deficiency was defined as a . . . [Full Text of this Article]