Public Interest in Vitamin C Supplementation During the COVID-19 Pandemic as a Potential Risk for Oxalate Nephrolithiasis

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INTRODUCTION: Vitamin C (ascorbic acid) therapy was widely touted as a potential treatment or preventive therapy for COVID-19 despite a lack of supporting evidence. One potential harm of high-dose vitamin C supplementation is increased urinary oxalate, which may increase the risk of hyperoxaluria and oxalate kidney stones. This study aims to evaluate public interest in vitamin C during the COVID-19 pandemic based on online search volume and to characterize variation in vitamin C interest as a potential contributor to kidney stone formation. Methods: The volume and frequency of online search traffic related to vitamin C and COVID-19 were assessed using the Google Trends platform (Google LLC, Mountain View, CA, USA) between 2018 and 2022. Weekly relative search volumes (RSV), the proportional volume of online searches for a search term, were assessed to compare variations in online interest in vitamin C and COVID-19. The most popular Google search results for vitamin C as a treatment for COVID-19 were assessed for medical accuracy. Statistical analysis was performed with t-tests and linear regression. RESULTS: Online search volume for vitamin C increased four-fold at the onset of COVID-19 in March 2020. After the initial outbreak, average RSV for vitamin C remained significantly elevated compared to pre-COVID-19 levels (37.7 vs. 25.1, p<0.001). Weekly RSV for vitamin C increased steadily during the study period (R2=0.59, p<0.001). The peak in online interest in vitamin C corresponded to increased online search volume during three global COVID-19 surges. Among the most popular results for COVID-19-related vitamin C queries, 30% inaccurately suggested that vitamin C had potential benefits in treating COVID-19. None of these search results discussed the potential increased risk of kidney stones with vitamin C supplementation. CONCLUSION: Online public interest in vitamin C supplementation increased and remained elevated during the COVID-19 pandemic. These findings have implications for increased risk of hyperoxaluria and oxalate stones due to vitamin C supplementation. Kidney stone patients should be counseled that excess vitamin C intake is associated with increased urinary oxalate and incident stone formation.

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