Effects of Curcumin Supplementation on Inflammatory Biomarkers in Adults with Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background/Objectives: Chronic low-grade inflammation contributes to the pathophysiology of type 2 diabetes mellitus (T2DM). This systematic review and meta-analysis evaluated randomized evidence on the effects of oral curcumin or curcuminoid supplementation on circulating inflammatory biomarkers in adults with T2DM. Methods: PubMed, Scopus, and Web of Science were searched from database inception through 31 August 2026. Random-effects models using restricted maximum likelihood (REML) and Hartung–Knapp confidence intervals were applied to the primary syntheses because relatively few studies contributed to each outcome. Results: Six randomized controlled trials (RCTs; n = 472) provided compatible hs-CRP endpoint data. Curcumin supplementation was associated with lower hs-CRP concentrations (MD = −1.06 mg/L; 95% CI −1.97 to −0.16; p = 0.030; I2 = 17.3%), although sensitivity analyses involving unit-ambiguous or statistically reconstructed data increased uncertainty. Five RCTs (n = 475) contributed quantitative TNF-α data; the pooled standardized effect favored curcumin (Hedges’ g = −1.20; 95% CI −1.98 to −0.42; p = 0.013), with substantial heterogeneity (I2 = 84.9%). Evidence for IL-6 from three randomized cohorts was directionally favorable but heterogeneous and was synthesized narratively, whereas IL-1β findings were limited to a single randomized cohort. Conclusions: Curcumin or curcuminoid supplementation may reduce hs-CRP and TNF-α in adults with T2DM; however, the strength of inference is limited by the small evidence base, heterogeneity, and inconsistencies in outcome reporting. Larger, methodologically standardized trials are warranted.