Timing-dependent effects of green tea supplementation and exercise intensity on oxidative stress in diabetic rats: a...

Exercise and green tea supplementation have been shown to attenuate oxidative stress in type 2 diabetes; however, their interactive effects across different exercise timings and intensities have not been systematically investigated. This study aimed to examine the interactive effects of exercise timing, exercise intensity, and green tea supplementation on oxidative stress in a rat model of type 2 diabetes using a factorial experimental approach. Fifty male Wistar rats were randomly assigned to eight experimental groups (n = 5 per group) in a 2 × 2 × 2 factorial design according to green tea supplementation form (Traditional green tea infusion vs. standardized green tea extract), exercise intensity (low vs. moderate), and exercise timing (morning light-phase vs. evening dark-phase). The intervention was conducted over 8 weeks and involved treadmill-based exercise training combined with oral green tea supplementation. Serum malondialdehyde (MDA) was the sole oxidative stress biomarker assessed in this study. MDA serum levels were measured as an index of systemic oxidative stress. Three-way analysis of variance revealed a significant interaction among green tea supplementation form, exercise intensity, and exercise timing on serum MDA levels (p = 0.0019, η ² = 0.26). All intervention groups demonstrated significantly lower MDA levels compared with diabetic controls (p < 0.05). The combination of standardized green tea extract with moderate-intensity exercise performed in the morning (light-phase) produced the greatest reduction in MDA levels and showed a trend toward normalization when compared with normal controls. These findings suggest that green tea supplementation, exercise intensity, and exercise timing do not act independently but interact in a timing-dependent manner to modulate oxidative stress in diabetic rats. However, interpretation of the observed morning (light-phase) advantage should consider the nocturnal nature of rodents, which may limit direct translation to human chronobiological exercise recommendations. Further studies incorporating multiple oxidative and metabolic markers and human trials are warranted.