This double-blind human trial found that Urolithin A (Mitopure) supplementation for 28 days in middle-aged adults enhanced mitochondrial function and revitalized immune cells. The compound increased younger and more active CD8⁺ T-cells, reduced immune exhaustion, and promoted fatty-acid oxidation. These results show that Urolithin A can safely boost cellular energy and counteract age-related immune decline, marking a breakthrough for nutraceutical-based mitochondrial therapy.