Letters Section Editor: Robert M. Golub, MD, Senior Editor.
To the Editor: Several factors affect serum 25-hydroxyvitamin D concentration, including age, smoking, renal function, adiposity, and body weight or body mass index.1 Furthermore, several conditions may affect the bioavailability of study participants' calcium supplementation, such as dosing with or without meals, the form of calcium supplement taken, the dosage taken at one time (>600 mg), coadministration with proton pump inhibitors, and vitamin D status.2 In the study of serum parathyroid hormone (PTH) levels, vitamin D sufficiency, and calcium intake by Dr Steingrimsdottir and colleagues,3 it is not clear if these factors have been considered.
Gau J, Clay S, Carlsen W. Parathyroid Hormone, Vitamin D, and Calcium Intake. JAMA. 2006;295(15):1769–1770. doi:10.1001/jama.295.15.1769-a
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