The Impact of Polyphenol-Rich Dark Fruits on Pain and Inflammation in Osteoarthritis: A Systematic Review and Meta-Analysis

Background: Osteoarthritis (OA) is a degenerative joint disease marked by pain, stiffness, and functional impairment, with inflammation central to its progression. Polyphenol-rich dark fruits, abundant in anthocyanins, possess antioxidant and anti-inflammatory properties that may mitigate OA-related mechanisms. This meta-analysis synthesized evidence from randomized controlled trials (RCTs) evaluating the effects of dark fruit supplementation on clinical symptoms and inflammatory biomarkers in individuals with OA. Methods: PubMed, Scopus, Web of Science, and three trial registries (ClinicalTrials.gov, WHO ICTRP, ISRCTN) were searched to September 2025 for RCTs comparing dark fruit supplementation with placebo, usual care, or no intervention. Two reviewers independently screened studies, assessed bias using Cochrane RoB, and evaluated certainty via GRADE (Grades of Recommendation, Assessment, Development and Evaluation). Data were pooled using random-effects models, with Hedges’ g as the standardized mean difference. Results: Six RCTs (215 participants; 3–16 weeks) investigating knee OA met inclusion criteria. Pooled analyses showed significant improvements in overall symptom severity (Hedges’ g = –0.31; 95% CI –0.57 to –0.05; P = 0.02), physical function (g = –0.34; 95% CI –0.66 to –0.05; P = 0.02), and interleukin-6 (IL-6, g = –0.40; 95% CI –0.79 to –0.01; P = 0.047). Where reported, compliance was generally high, although adherence and adverse-event reporting were incomplete across trials. Evidence certainty was low, with moderate-to-high risk of bias. Discussion: In the available RCT evidence, which was restricted to knee OA, dark fruit supplementation was associated with small short-term improvements in selected OA symptoms and IL-6. However, findings are limited by low certainty of evidence, short intervention durations, incomplete adherence and adverse-event reporting, and the absence of long-term or structural outcomes; therefore, no conclusions can be drawn regarding disease-modifying effects or longer-term tolerability. Larger, high-quality trials are needed to determine whether polyphenol-rich fruits provide clinically meaningful benefits in OA management.