1,25-dihydroxycholecalciferol and parathyroid hormone in advanced chronic renal failure: effects of simultaneous protein and phosphorus restriction.

Vitamin D3 metabolites and immunoreactive parathyroid hormone (iPTH) were measured in sera obtained from subjects with advanced chronic renal failure (CRF) (creatinine clearance less than 10 ml/min) before and after 3 months on a diet very low in protein (less than 0.2 g/kg/day), phosphorus (less than 500 mg/day), and supplemented with a mixture of essential amino acids and ketoacid analogues of essential amino acids. iPTH and phosphate fell in all subjects (p less than 0.02). 1,25-dihydroxycholecalciferol (1,25[OH]2D3) fell in all but one of the subjects (p less than 0.02), while no significant change was seen in creatinine clearance or in serum 25-hydroxycholecalciferol (25[OH]D3) levels. A strongly positive correlation was found between initial serum levels of 25(OH)D3 and 1,25(OH)2D3 (r = 0.95, p less than 0.001). Thus in contrast with the reported effects of dietary phosphorus reduction in subjects with early and moderate CRF and in normal subjects, this regime was associated with decreased 1,25(OH)2D3 levels in subjects with advanced CRF.