Anti-inflammatory effects of oral supplementation with curcumin: a systematic review and meta-analysis of randomized controlled trials

Abstract Context Chronic inflammation is a major contributor to the development of noncommunicable diseases. Curcumin, a bioactive polyphenol from turmeric, is a well-known anti-inflammatory agent in preclinical research. Clinical evidence remains inconclusive because of discrepancies regarding optimal dosage, duration, and formulation of curcumin. Objective The aim of this systematic review, conducted and reported in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and checklist, was to evaluate the efficacy of curcumin supplementation on systemic inflammatory mediators, comparing dose, duration, and bioavailability status of interventions. Data Sources The Medline, CINAHL, EMBASE, Scopus, and Cochrane literature databases were searched from 1980 to May-end 2019. Randomized controlled trials investigating effects of dietary curcumin on inflammatory mediators in humans not receiving anti-inflammatory treatment were eligible for inclusion. Two authors independently assessed titles and abstracts of identified articles for potential eligibility and respective, retrieved, full-text articles; disagreements were resolved by a third author. Evidence quality was critically appraised using the Quality Criteria Checklist for Primary Research. Data Extraction Thirty-two trials (N = 2,038 participants) were included and 28 were meta-analyzed using a random-effects model; effect sizes were expressed as Hedges’ g (95%CI). Data Analysis Pooled data (reported here as weighted mean difference [WMD]; 95%CI) showed a reduction in C-reactive protein (−1.55 mg/L; −1.81 to −1.30), interleukin-6 (−1.69 pg/mL, −2.56 to −0.82), tumor necrosis factor α (−3.13 pg/mL; −4.62 to −1.64), IL-8 (−0.54 pg/mL; −0.82 to −0.28), monocyte chemoattractant protein-1 (−2.48 pg/mL; −3.96 to −1.00), and an increase in IL-10 (0.49 pg/mL; 0.10 to 0.88), with no effect on intracellular adhesion molecule-1. Conclusion These findings provide evidence for the anti-inflammatory effects of curcumin and support further investigation to confirm dose, duration, and formulation to optimize anti-inflammatory effects in humans with chronic inflammation. Systematic Review Registration PROSPERO registration no. CRD42019148682.