Short- and long-term effects of capsaicin supplementation on glycemic control: a systematic review and meta-analysis of controlled trials.

Background & aims Animal studies have shown that capsaicin exerts beneficial effects on glucose metabolism. However, the findings of human studies are contradictory. Therefore, we aimed to conduct a systematic review and meta-analysis of controlled trials to assess the effect of capsaicin administration on glycemic indices. Methods Medline, Scopus, Cochrane Library, and Google Scholar were searched from the database inception to January 14, 2021. The weighted (WMD) or standardized (SMD) mean difference with 95% confidence interval (CI) was calculated using a random-effects model. Results Fourteen trials were included in this study. Long-term capsaicin supplementation did not show significant effects on fasting blood glucose (WMD: 0.03 mmol L-1, 95% CI: -0.05 to 0.12, I2 = 40.5%) and fasting insulin (SMD: 0.09, 95% CI: -0.04 to 0.22, I2 = 0.0%). Short-term capsaicin supplementation had no significant effects on 2-hour postprandial blood glucose (WMD: 0.06 mmol L-1, 95% CI: -0.34 to 0.47, I2 = 92.5%) and 2-hour postprandial insulin (WMD: 1.70 μIU mL-1, 95% CI: -3.46 to 6.86, I2 = 72.4%). Subgroup analysis revealed that the dose and ingestion form of capsaicin could be sources of between-study heterogeneity. Conclusions Capsaicin supplementation seems to have neither acute nor chronic beneficial or detrimental effects on blood glucose and insulin levels.