Publications

Purpose In patients with Primary Hyperparathyroidism (PHPT) vitamin D defciency has been associated with more severe presentations. Our aim was to investigate the efects of Vitamin D supplementation on mineral homeostasis and related hormones in individuals with and without PHPT. Methods Individuals with and without PHPT (CTRL) received 14,000 IU/week of oral vitamin D3 for 12 weeks. At baseline and endpoint, blood samples were collected to measure 1,25(OH)2vitamin D (1,25(OH)2D), intact Fibroblast Growth Factor 23 (FGF23), 25OHD, Parathormone, and other biochemical markers. The 1,25(OH)2D measurement was performed using liquid chromatography and mass spectrometry (LC–MS/MS). Results 70 PHPT patients and 75 CTRL were included, and 55 PHPT and 64 CTRL completed the 12-week protocol. After the intervention, there were signifcant increases in the FGF23 levels (PHPT: 47.9±27.1 to 76.3±33.3; CTRL: 40.5±13.9 to 59.8±19.8 pg/mL, p<0.001), and signifcant decreases in 1,25(OH)2D levels (PHPT: 94.8±34.6 to 68.9±25.3; CTRL: 68.7±23.5 to 56.4±20.7 pg/mL, p<0.001). The reduction of 1,25(OH)2D was inversely associated with the increase of FGF23 in both the PHPT (r=−0.302, p=0.028) and CTRL (r=−0.278, p=0.027). No changes in plasmatic or uninary calcium concentrations were observed in both groups. Conclusion The weekly administration of 14,000 IU of Vitamin D3 was safe and efcient to increase in 25OHD levels in both groups. However, a paradoxical decrease in 1,25(OH)2D levels measured by LC–MS/MS was associated with a signifcant increase in FGF23 levels in both groups. This phenomenon might represent a defense against hypercalcemia after vitamin D supplementation and paves the way for new studies in this regard.