Dietary vitamin D intake in advanced CKD/ESRD.

In healthy individuals, vitamin D produced in the skin or derived from nutritional sources is converted to 25-hydroxyvitamin D (25[OH]D) in the liver, and then 1,25-dihydroxyvitamin D (1,25[OH](2)D) by 1 alpha-hydroxylase in the kidney. Chronic kidney disease (CKD) is accompanied by a progressive decline in the ability to produce 1,25(OH)(2)D; thus, replacement of this hormonal form of vitamin D has been the focus of therapeutic interventions to prevent and treat complications such as hypocalcemia, and secondary hyperparathyroidism. New research suggests that conversion of 25(OH)D to 1,25(OH)(2)D outside of the kidney may have important biological roles beyond those traditionally ascribed to vitamin D. 25(OH)D levels have increasingly been linked to important clinical outcomes in CKD. This article reviews vitamin D metabolism, emerging new roles for vitamin D, and data surrounding the potential importance of nutritional sources of vitamin D in the management of patients with CKD.