Impact of vitamin C on parathormone secretion in patients on hemodialysis with secondary hyperparathyroidism

Secondary hyperparathyroidism is a complication of chronic kidney disease, and it develops due to abnormal regulation of calcium and phosphate homeostasis (1). Various factors interact in its development. They are consist of decrease kidney synthesis of 1,25-dihydroxyvitamin D, the, phosphorus retention and impaired calcemic response to parathyroid hormone (1,2). Hence, increasing of parathormone synthesis, and parathyroid cell hyperplasia will happen. High serum levels of parathormone, considered as a uremic toxin, which can stimulate accelerated bone absorption and reabsorption, and cause bone demineralization and kidney osteodystrophy (1-4). The bones which become demineralized are structurally fragile and easily broken, and they are not resistant to any shock. At this stage, there is higher risk of fractures (2-5). On the other hand, there is a risk factor for ectopic calcification and cardiovascular disease in patients on hemodialysis too (1-5). Secondary hyperparathyroidism often happens in stage three of chronic kidney disease, before the development of hyperphosphatemia. To prevent the various troubles originated by secondary hyperparathyroidism, it is mandatory to reduce high parathyroid hormone to an acceptable level in hemodialysis patients (3-6). Various, active vitamin D analogs, which can strongly suppress parathyroid hormone, have become available for treatment, however, their yield are limited (2-7). According to various investigations, phosphate binders frequently result in unfavorable side effects and imbalance in bone metabolism (4-7). Thus, new therapies with fewer side effects is reasonable. In fact, there is a potential association between the occurrence of secondary hyperparathyroidism and low vitamin C levels (8,9). Vitamin C supplementation is possibly a modality to reduce parathormone with less side effects, while several investigations have shown, increasing vitamin C levels by dietary supplementation resulted in reduction of parathormone in vitamin C-deficient individuals on regular hemodialysis with secondary hyperparathyroidism (8,9). Investigations, have shown, in low serum levels of vitamin C, calcium-sensing receptors may become resistant to parathormone effects. Vitamin C increases the response to parathormone at the receptor level, through increasing the cyclic adenosine Implication for health policy/practice/research/ medical education Increased parathormone can stimulate bone demineralization and lead to high-turnover bone disease; a situation marked by accelerated rates of bone absorption and reabsorption. This condition defined as secondary hyperparathyroidism and requires treatment. Various studies have shown the contradictory effect of vitamin C on parathormone secretion, however some of the investigations showed its beneficial property to lower serum parathormone level. Patients on hemodialysis are at risk for low levels of serum vitamin C too. Vitamin C is a watersoluble substance which can be reduced by routine hemodialysis. This subject, however needs further investigation with larger samples, to fully define the impact of vitamin C on parathormone secretion.