Grapes, particularly the seeds and skins, are rich in polyphenolic compounds such as resveratrol, quercetin, and proanthocyanidins, which have been extensively studied for their antioxidant properties. Free radical damage, also known as oxidative stress, involves the harmful effects of unstable molecules (free radicals) on cellular components. Antioxidants neutralize these free radicals and reduce oxidative damage, which has been implicated in aging, cardiovascular diseases, and cancer.

Numerous in vitro and animal studies have demonstrated that grape extracts can scavenge free radicals and protect cells from oxidative injury. Human studies, though fewer, also suggest potential benefits. For example, a number of clinical trials have shown that supplementation with grape seed extract leads to a significant increase in antioxidant capacity in the blood and reduction in markers of oxidative stress. Resveratrol, in particular, has been shown to modulate signaling pathways that protect against oxidative damage.

While more large-scale human trials are needed to confirm the clinical relevance, the current body of scientific evidence strongly supports the use of grape-derived products as antioxidants to help counteract free radical damage. Thus, the use of grape for this purpose is primarily justified by scientific research.