Vitamin C deficiency and secondary hyperparathyroidism in chronic haemodialysis patients

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 mu M to > 300 mu M. We found 15% (n = 17) of the patients with severe vitamin C deficiency (< 10 mu M), 66% (n = 77) in the range 10-80 mu M, and 19% (n = 23) with plasma vitamin C > 80 mu M, 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.