A case report of renal oxalosis and secondary hyperoxaluria due to chronic high vitamin C consumption

Renal oxalosis occurs from supersaturation of the urine with oxalate in the presence of calcium, resulting in deposition of calcium oxalate crystals within renal tissue and, consequently, progressive renal disease. One of the causes of secondary hyperoxaluria is a high intake of vitamin C, which exceeds the renal excretion capacity, and can induce renal oxalosis. We present a case involving a 67-year-old patient with chronic kidney disease and proteinuria, associated with secondary hyperoxaluria and renal oxalosis, who reported prolonged, excessive intake of vitamin C supplements. The patient presented with a gradual worsening of his renal function and proteinuria during the last 6-month period, after an episode of SARS-CoV-2 infection. The kidney biopsy revealed calcium oxalate crystals within the renal tissue. Thorough investigation and history-taking revealed a substantial increase in vitamin C supplementation during the SARS-CoV-2 infection (up to 3 g daily), indicating secondary hyperoxaluria as the causative factor. Overall during the pandemic, supplement consumption dramatically increased and patients were not adequately informed about the risks of various over-the-counter products. Excessive intake of vitamin C, popularized for its supposed health benefits, can lead, among others, to secondary hyperoxaluria and renal oxalosis. Prompt recognition is pivotal to initiate management and to prevent irreversible kidney damage.