Acute and Chronic Effects of Green Tea Kombucha With and Without Grape Skin Extract on Immune and Oxidative Stress Markers in Beginner Runners: A Randomized Controlled Trial.

Green tea kombucha is an antioxidant-rich beverage with promising health benefits. However, evidence regarding its effects in physically active individuals remains limited. This study investigated the acute and chronic effects of green tea kombucha, with or without grape skin extract, on immune and oxidative stress markers in beginner runners. This 12-week randomized clinical trial included 90 healthy adults (18-45 years) allocated to three groups: control (CT-G), green tea kombucha (GT-G), and green tea kombucha with grape skin extract (GTG-G). Participants performed supervised running training three times weekly following a polarized periodization model. Kombucha intake was not associated with significant changes in the primary outcome, ferric reducing antioxidant power (FRAP), nor in acute immune or oxidative responses to exercise (p > 0.05). However, during the chronic period, the GT-G showed increased neutrophils (p = 0.026) and reduced lymphocytes (p = 0.023) compared to the other groups. Fasting catalase (CAT) activity differed between groups GT-G and CT-G (p = 0.037), despite no significant group x time interaction (p = 0.157). A group × time interaction was detected for post-exercise malondialdehyde concentrations (p = 0.033), with no significant interaction in the post hoc test. Sensitivity analyses including all randomized participants confirmed the primary observations; however, false discovery rate (FDR) adjustments indicated these findings are exploratory. No additional effects were detected in GTG-G. In conclusion, 12 weeks of green tea kombucha intake was associated with nominally significant changes in immune and oxidative markers during chronic running training, and further studies are needed to clarify these findings.