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Normal vitamin C intake (from food or ≤100-200 mg supplements) is safe. Mega-doses (1,000+ mg/day) convert to oxalate and cause kidney stones and, in CKD, oxalate nephropathy. In dialysis, vitamin C dosing has specific rules.
Vitamin C is metabolized to oxalate — its waste product. At high doses, urine oxalate rises sharply, driving calcium-oxalate stones (the most common stone type).
In CKD, oxalate clearance falls, so supplement-derived oxalate accumulates — case reports document oxalate nephropathy (crystal damage to kidney tissue) from mega-dose vitamin C.
Routine high-dose IV vitamin C in ICUs has caused acute oxalate kidney injury in case series.
Recommended: get vitamin C from food (fruits, vegetables — with potassium awareness in CKD); limit supplements to 100-200 mg/day unless a deficiency is documented; dialysis patients typically have specific modest dosing protocols.
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This content is a general reference, not medical advice, a diagnosis, or a treatment plan. Do not change your diet, fluids, medicines, or dialysis plan without your nephrologist or renal dietitian. Individual recommendations depend on your labs, medications, conditions, and care plan.