Vitamin C and Benzoic Acid Intake in Patients with Kidney Disease: Is There Risk of Benzene Exposure?

Vitamin C is a small water-soluble molecule primarily cleared by the kidneys. Therefore, its plasma concentration would be expected to increase as kidney function declines. However, studies in patients with chronic kidney disease (CKD) and kidney transplant recipients have shown the opposite: a positive correlation between kidney function and plasma vitamin C levels. In this review, we discuss potential explanations for this counterintuitive finding and suggest alternative mechanisms influencing vitamin C bioavailability in this population. We also explore the hypothesis that this phenomenon may be linked to benzoic acid (benzoate) exposure. Benzoic acid is a widely used food preservative that, like vitamin C, is water-soluble and renally excreted. In individuals with impaired kidney function, reduced clearance may lead to elevated circulating benzoic acid levels, which could increase the likelihood of an in vivo chemical reaction between benzoic acid and vitamin C, resulting in the formation of benzene, which is a known toxic and carcinogenic compound. We summarize experimental evidence demonstrating the vitamin C–benzoic acid reaction in vitro, along with preliminary animal studies suggesting it may also occur in vivo. We also discuss the potential clinical consequences of benzene exposure in the context of patients with kidney function impairment. Given the widespread use of benzoic acid as a food preservative and the ongoing discussion around vitamin C supplementation in patients with kidney disease, this review invites further investigation to evaluate whether this reaction represents a health hazard for this population.