Bone mass and dynamic parathyroid function according to bone histology in nondialyzed uremic patients after long-term protein and phosphorus restriction

One year of a very low protein diet (VLPD) can reverse secondary hyperparathyroidism in uremic patients. We studied bone histology, bone mineral density (BMD), and dynamic parathyroid function (calcium/PTH curves) in 16 nondialyzed patients with advanced renal failure who had been receiving a VLPD for a mean of 5 yr (mean protein intake, 0.34 +/- 0.12 mg/kg day; mean phosphorus intake, 8.2 +/- 2.1 mg/kg day) and daily supplementation with essential amino acids and their ketoanalogs (1000 IU vitamin D-2 and 1-2 g calcium carbonate). Three patients exhibited a high bone formation rate (BFR), 7 patients had normal bone remodeling, and 6 patients had a low BFR, including 2 with osteomalacia and 4 with adynamic bone disease without aluminum overload. A longer diet duration and lower caloric intake were associated with low BFR. More than half of the patients exhibited moderate or severe osteoporosis at the appendicular skeleton. The t score of femur BMD explained 65% of the BFR variance. Patients with a low BFR had a dynamic parathyroid function similar to that of patients with a normal BFR, except they had a lower capacity to buffer a calcium load, whereas patients with a high BFR had a higher basal PTH/maximum PTH and a steeper calcium/PTH curve slope; the calcium set-point was identical in the three groups.