Twelve-Week Curcumin Supplementation Improves Glucose Homeostasis and Gut Health in Prediabetic Older Adults: A Pilot, Double-Blind, Placebo-Controlled Trial

Abstract

Background: The prevalence of diabetes increases with age, and food bioactive compounds have shown potential in mitigating its development. This study aimed to evaluate the efficacy of curcumin in preventing type 2 diabetes mellitus (T2DM) in older adults with prediabetes. We hypothesized that curcumin, due to its insulin-sensitizing effects, would help maintain glucose homeostasis, metabolic health, and gut health. Methods: This randomized, double-blind, placebo-controlled trial included 28 older adults (aged 60 years or older) with prediabetes or overweight/obesity. Participants were randomly assigned to receive either curcumin (80 mg) or placebo capsules for 12 weeks. The primary outcome measures were glucose homeostasis markers, including hemoglobin A1c (HbA1c), blood glucose, and insulin levels. Secondary outcomes included body composition, body mass index (BMI), body weight, lipid profiles, and gut microbiome composition. Data normality was assessed using the Shapiro-Wilk test, and two-way repeated-measures ANOVA with multiple comparisons was used to find differences between groups and over time. Results: A total of 23 participants (age = 66.52 ± 5.76 years; 14 in the curcumin group and 9 in the placebo group) completed the 12-week intervention. HbA1c levels significantly decreased in the curcumin group, whereas levels remained stable in the placebo group. While the curcumin group observed an increase in AST levels, the ALT level was reduced in the placebo group. Both the curcumin and placebo groups showed a reduced ALT/AST ratio by the end of the intervention. Body mass index, lipid profiles, and body composition showed no significant changes over the study period. Gut microbiome analysis revealed no significant changes in alpha diversity or beta diversity of microbiome; however, there was marginal enrichment of beneficial bacteria such as Bacteroidota (phylum), Bacteroidaceae (family), Agathobacter, Bacteroides, and Roseburia (genera) in the curcumin-supplemented group over time. Conclusions: Curcumin supplementation improved or favorably maintained glucose homeostasis and showed modest improvements in beneficial gut microbiota in older adults with prediabetes, potentially reducing the risk of developing diabetes. Long-term studies with larger sample sizes are needed to confirm these findings and determine the clinical relevance of curcumin supplementation for prediabetes prevention.

Keywords: HbA1c; curcumin; geriatric diabetes; glucose homeostasis; gut microbiome; type 2 diabetes prevention.

Figure 1

CONSORT diagram illustrating the progression of participants through each stage of the study, including screening, randomization, allocation to intervention groups, follow-up, and analysis.

Figure 2

No significant changes in alpha or beta diversity of the gut microbiome were observed following the 12-week intervention: (A) observed ASVs, (B) Pielou’s Evenness Index, (C) Shannon Index, (D) Weighted UniFrac distance, and (E) unweighted UniFrac distance for the curcumin and placebo groups. Pre: before supplementation; Post: after intervention; Pla: placebo; and CUR: curcumin.

Figure 3

Twelve weeks of curcumin supplementation modestly alters gut microbial composition in older adults. The figure represents microbial composition at the (A) phylum, (B) family, (C) genus, and (D) ASVs levels. Pre: before supplementation; Post: after intervention; Pla: placebo, and CUR: curcumin.