Vitamin C deficiency and secondary hyperparathyroidism in chronic haemodialysis patients

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Abstract

Background

Maintenance haemodialysis patients often suffer from secondary hyperparathyroidism and serum parathyroid hormone levels may be influenced by nutritional variables.

Methods

We examined serum bio-intact parathyroid hormone (BiPTH) and plasma vitamin C in 117 chronic haemodialysis patients. Plasma vitamin C was measured by high-performance liquid chromatography with electrochemical detection, on samples collected before start of the dialysis treatment.

Results

Plasma vitamin C showed a significant positively skewed distribution, ranging from <2 μM to >300 μM. We found 15% (n=17) of the patients with severe vitamin C deficiency (<10 μM), 66% (n=77) in the range 10–80 μM, and 19% (n=23) with plasma vitamin C >80 μM, the upper limit of normal for non-renal disease population. High plasma vitamin C was associated with lower plasma BiPTH (P=0.005, one-way analysis of variance), and this association persisted after stepwise multiple regression for other factors known to influence PTH. Low vitamin C levels were also associated with increased serum alkaline phosphatase, a further indicator of the impact of vitamin C status on bone metabolism. Patients who reported dietary vitamin C intake of ≥100 mg/day had lower BiPTH (P=0.015), consistent with findings from plasma measurements of vitamin C. This novel observation of the interaction between PTH and vitamin C may result from effects of vitamin C on cAMP-linked signalling pathways in bone and parathyroid gland.

Conclusions

This finding does not yet warrant therapeutic intervention with supplemental vitamin C to remedy secondary hyperparathyroidism. However, further research may indicate a key interaction between vitamin C and the parathyroid hormone linked signalling pathways, and may uncover mechanisms of therapeutic importance.

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