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Titolo	Vitamin C deficiency in dialysis patients - are we perceiving the tip of an iceberg?
Autore	G.J. Handelman
Referenza	Nephrol Dial Transplant 2006; doi: 10.1093/ndt/gfl534
Contenuto	The occurrence of vitamin C deficiency has complicated the management of dialysis patients since the beginning of renal replacement therapy [1]. The major portion of dietary vitamin C is provided by potassiumrich foods such as orange juice, strawberries and broccoli, but these foods are restricted for haemodialysis (HD) patients because HD removes potassium with limited efficiency. Hyperkalaemia is potentially a major risk factor for dialysis morbidity and mortality [2], and one of the chief responsibilities of the renal dietitian is to instruct the patient to limit the intake of potassium-rich foods [3]. Under these circumstances, low dietary vitamin C intake can readily occur. Since vitamin C is partly metabolized to oxalate, which can accumulate in renal failure patients, many clinicians only recommend a dose of 60-100 mg/day, which may not be optimal. The problem is made more severe by vitamin C losses during dialysis, which may remove several hundred mg of vitamin C in a single dialysis treatment [4,5]. Plasma vitamin C in dialysis patients is frequently <10 mM [6], a level associated with scurvy in the non-dialysis population. Normal plasma vitamin C levels in the non-dialysis population are 30-60 mM [7]. Very high levels of vitamin C can also occur in dialysis patients. The normal kidney clears vitamin C when the plasma level exceeds 60 mM [8], but the effect of dialysis on vitamin C is highly variable. For patients who take large vitamin C supplements, the lack of the normal renal clearance mechanism can result in very high plasma levels (>200 mM) [9]. Vitamin C deficiency can interfere with iron absorption and utilization, as well as leading to various abnormalities that are part of the syndrome of scurvy. The occurrence of widespread vitamin C deficiency in dialysis patients calls for greater attention to these clinical problems.
Data	07.12.2006

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