Calcium balance in normal individuals and in patients with chronic kidney disease on low- and high-calcium diets

Calcium balance in chronic kidney disease is poorly understood as calcium deficiency is a stimulus for secondary hyperparathyroidism and consequent bone loss while calcium excess promotes extraosseous calcifications. To help resolve this, we evaluated calcium balance in normal individuals and in patients with chronic kidney disease (CKD) on daily diets containing 800 and 2000 mg elemental calcium. Both normal individuals and patients with late stage 3 and stage 4 CKD were in slightly negative to neutral calcium balance on the 800-mg calcium diet. Normal individuals were in modest positive calcium balance on the 2000-mg diet, while patients with CKD on the same diet were in marked positive calcium balance at least over the 9 days of study; and significantly greater than the normal individuals. Increased calcium intake significantly decreased 1,25-dihydroxy-vitamin D and intact parathyroid hormone levels but did not alter the serum calcium concentration. Thus, our findings have important implications for both preventing calcium deficiency and loading in individuals with late stage 3 and stage 4 CKD.