Serum calcitriol and dietary protein intake in idiopathic calcium stone patients

In kidney stone patients, high protein intake and calcitriol overproduction are factors leading to hypercalciuria, but there are conflicting reports o n the effects of dietary protein on calcitriol production. To investigate t he relationships between serum calcitriol, dietary protein intake, and urin ary calcium excretion, 33 male idiopathic calcium stone formers (aged 20-60 years), with normal renal function and on unrestricted diet, have been stu died. Dietary protein intake was estimated by the protein catabolic rate de termination. Abnormally elevated calcitriol levels were found in 16 patient s (48.5%) who had similar levels of serum intact parathyroid hormone and ph osphate, creatinine clearance, and calcium and phosphate urinary excretion, but lower protein catabolic rate (82+/-16 vs. 97+/-20 g/day, P<0.05) than the patients with normal calcitriol levels. The calcitriol to intact parath yroid hormone ratio was higher in hypercalciuric than in normocalciuric pat ients (2.4+/-1.1 vs. 1.6+/-0.8, P<0.05). Calcitriol was positively correlat ed with plasma calcium (r=0.41, P<0.01) and inversely with protein cataboli c rate (r=-0.42, P<0.01). Protein catabolic rate was positively correlated with creatinine clearance (r=0.69, P<0.001) and urinary phosphate excretion (r=0.72, P<0.001). No relationship was observed between calcitriol and cre atinine clearance. These results confirm the calcitriol overproduction in c alcium stone disease and that the high calcitriol to intact parathyroid hor mone ratio is the main feature associated with hypercalciuria. Calcitriol s erum levels appear to be unrelated to creatinine clearance, whereas there i s an inverse relationship with protein catabolic rate. This suggests that l ow rather than high dietary protein intake may favor the increase of calcit riol synthesis in male calcium stone formers with normal renal function.