The Importance of Phosphate in Regulating Plasma 1,25-(OH)2-Vitamin D Levels in Humans: Studies in Healthy Subjects, in Calcium-Stone Formers and in Patients with Primary Hyperparathyroidism*

Abstract

Plasma 1,25-(OH)2-D concentrations average 87 .+-. 30 SD pmol/l in 48 healthy adults without a personal or family history of kidney stones. Plasma 1,25-(OH)2-D concentrations were significantly elevated among 26 patients with recurrent calcium-containing renal stones and hypophosphatemia: 150 .+-. 74 pmol/l; P < 0.001, and among 9 patients with proven parathyroid adenoma and hypophosphatemia: 200 .+-. 54 pmol/l; P < 0.001. Plasma 1,25-(OH)2-D levels in these 3 groups were inversely correlated with serum phosphate concentration: plasma 1,25-(OH)2-D, pmol/l = 282 - 141 .times. serum PO4, mmol/l; r = 0.51; P < 0.001. During dietary PO4 deprivation lasting 11 to 16 days in 10 healthy women, serum PO4 fell and plasma 1,25-(OH)2-D concentrations rose whereas in 8 healthy men neither serum PO4 nor 1,25-(OH)2-D concentrations changed. The change from control in plasma 1,25-(OH)2-D levels were correlated with the change from control in serum PO4 concentrations: .DELTA.1,25-(OH)2-D, pmol/l = 1 - 82 .times. .DELTA.serum PO4 mmol/l; r= 0.59; P < 0.01. Reductions in serum PO4 concentrations, either directly or indirectly, stimulate renal synthesis of 1,25-(OH)2-D in humans.