Objective

PTH can be oxidised in vivo, rendering it biologically inactive. Non-oxidised PTH (n-oxPTH) may therefore give a better image of the hormonal status of the patient. While vitamin D supplementation decreases total PTH (tPTH) concentration, the effect on n-oxPTH concentration is unexplored. We investigated the effect of vitamin D on n-oxPTH concentration in comparison to tPTH and compared the correlations between parameters of calcium, bone and lipid metabolism with n-oxPTH and tPTH.

Design

Randomized clinical trial

Methods

N-oxPTH was measured in 108 vitamin D insufficient (25(OH)D<75 nmol/L) hypertensive patients, treated with vitamin D (2800 IE daily) or placebo for 8 weeks in the Styrian Vitamin D Hypertension Trial (NCT02136771). We calculated the treatment effect and performed correlation analyses of n-oxPTH and tPTH at baseline with parameters of calcium, bone and lipid metabolism.

Results

After treatment, 25(OH)D concentrations increased, tPTH decreased by 9% (p<0.001) and n-oxPTH by 7% (p=0.025). Also, the ratio of n-oxPTH/tPTH increased (p=0.027). N-oxPTH showed a significant correlation with tPTH (r=0.555, p<0.001), osteocalcin (r=0.237, p=0.014), HDL (r=0.254; p<0.001) and triglycerides (r=-0.216; p=0.025). tPTH had no significant correlation with osteocalcin, HDL or triglycerides.

Conclusions

We showed that both tPTH and n-oxPTH decrease upon vitamin D supplementation. In addition, our study suggests that vitamin D supplementation reduces the oxidation of PTH, as we observed a small but significant decrease in the oxidised proportion of PTH upon treatment. Further research should be carried out to establish the clinical relevance of n-oxPTH and the role of oxidation in PTH-based therapies.