Buyer Beware: Evidence-Based Evaluation of Dietary Supplements for Nephrolithiasis

Introduction: Numerous dietary supplements claiming to treat or prevent kidney stones have recently been brought to the market. However, the evidence for these claims is not clear. This study assesses the scientific evidence supporting dietary supplements for the treatment and prevention of urinary stone disease. Materials and Methods: Two online marketplaces (Amazon and Google) were queried for dietary supplements available without a prescription to treat, alleviate, or prevent stone disease. Product labels were reviewed to compile stone-related claims and active ingredients. The 30-day cost of treatment and consumer star rating were assessed. MEDLINE, Web of Science, and Google Scholar were queried with labeled ingredients to assess the scientific evidence from published and lay sources. Results: A total of 27 dietary supplements containing 56 ingredients were analyzed. Supplements made a variety of claims, including dissolving stones (12 products, 44%), preventing stone formation (7 products, 26%), and reducing stone symptoms (6 products, 22%). Mean 30-day cost was $32 (range $4-$189). All products were rated highly by consumers (mean 4.2 of 5 stars). Of the 56 ingredients, 9 (16%) had any published studies for use in stone disease, and 5 (9%) had exclusively studies supporting their use. Eighteen scientific publications about the ingredients were identified, of which six showed mixed or no benefit in stone disease. Overall, 18 (67%) supplements contained ingredients with conflicting or absent evidence of benefit. No association was found between product cost or rating and products containing ingredients supported by human or animal studies (p > 0.05). Conclusions: Two-thirds of dietary supplements claiming to treat or prevent kidney stones contain ingredients with conflicting or no scientific evidence to support their claims. Clinicians should counsel stone formers that the effects of most supplements are unknown or unstudied in humans, and that the absence of evidence does not imply absence of potential harm.