Anthocyanin-Rich Aronia melanocarpa Supplementation Modulates Intestinal Barrier Biomarkers and Stress-Axis Response in a Randomized Controlled Trial

Background: Anthocyanin-rich berries may modulate intestinal barrier-related processes and physiological stress responses, but evidence from human studies remains limited. Methods: This randomized, double-blind, placebo-controlled trial included 15 elite male rowers (Aronia group, n = 7; placebo group, n = 8). Participants received Aronia melanocarpa supplementation or placebo for eight weeks and performed a standardized 2000-m rowing ergometer test before and after the intervention. Circulating claudin-3 (CLDN-3), lipopolysaccharide-binding protein (LBP), intestinal fatty acid-binding protein (I-FABP), and cortisol concentrations were assessed before exercise, immediately after exercise, and following 1 h of recovery. Results: A significant Group × Time interaction was observed for CLDN-3 (p = 0.0463). After eight weeks, pre-exercise CLDN-3 concentrations were lower in the Aronia group than in the placebo group (p = 0.0367). Lower pre-exercise LBP concentrations (p = 0.0125) and lower cortisol concentrations at 1 h post-exercise (p = 0.0079) were also observed in the Aronia group compared with placebo. No significant supplementation-specific effect was observed for I-FABP. Conclusions: Eight weeks of Aronia melanocarpa supplementation was associated with differences in selected intestinal barrier-related biomarkers and post-exercise cortisol concentrations in elite male rowers. However, these findings were primarily related to specific sampling time points and should not be interpreted as evidence of improved intestinal barrier function. Given the small sample size and potential dietary confounding, the results are preliminary and require confirmation in larger randomized controlled trials.