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, I-2 = 40.5%) and fasting insulin (SMD: 0.09, 95% CI: -0.04 to 0.22, I-2 = 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, I-2 = 92.5%) and 2-hour postprandial insulin (WMD: 1.70 mu IU mL(-1), 95% CI: -3.46 to 6.86, I-2 = 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.