Vitamin D deficiency will be defined as 25(OH)D levels less than 20 ng/mL (50 nmol/L) and vitamin D insufficiency as 21 to 29 ng/mL (50 to 80 nmol/L). Secondary hyperparathyroidism will be defined as iPTH ≥ 70 ng/L. An increase in serum intact PTH level will be taken to be indicative of a possible negative calcium balance or a vitamin D deficiency (or both). Hypercalcemia will be defined as calcium > 2.63 mmol/L.