Citric acid concentration compared to serum parathyroid hormone, 1,25(OH)2D3 and calcitonin during dietary Ca deficiency and rehabilitation enhanced with xylitol in rats.

Young male Wistar rats were fed on a Ca-deficient diet for 3 weeks, after which dietary Ca was restored with either CaCO3 or CaCO3 + xylitol (5% per weight). Citric acid, Ca, Mg, Zn and P were determined in the tibia and femur at the beginning and after 2 and 4 weeks of rehabilitation, and serum and urinary citric acid and serum 1,25(OH)2D3, parathyroid hormone (PTH) and calcitonin were measured at the same points in time. The diminished bone Ca (p < 0.001) after 3 weeks of deficiency did not reduce the bone citric acid concentration, although serum citrate increased markedly. Simultaneously the serum 1,25(OH)2D3 concentration more than doubled and PTH increased (p < 0.01). Rehabilitation with CaCO3 + xylitol reduced the 1,25(OH)2D3 concentration to below the control level (p < 0.05), while serum citric acid remained elevated. CaCO3 alone normalized the elevated hormone and citric acid levels in the serum. Dietary CaCO3 and CaCO3 + xylitol normalized the PTH concentration equally well. The gain in bone Ca after 4 weeks of rehabilitation was significantly greater when xylitol was added compared with CaCO3 alone (p < 0.05). Only the 4-week CaCO3 + xylitol group attained the bone Ca concentration of the controls. Xylitol supplementation seems to affect the serum citric acid concentration independent of 1,25(OH)2D3 and PTH concentrations. The elevated citric acid concentration could be associated with increasing bone Ca.