Across 5 randomized controlled trials, all 5 reported small beneficial effects of red grape (primarily grape seed extract) supplementation on reducing mean arterial pressure (MAP). Effects were observed in short-term studies (median duration 7 days) and in populations including men with prehypertension, overweight/obese individuals, and NAFLD patients. The most commonly tested doses were 300 mg (single dose) and 520 mg/day, though dose reporting was inconsistent.
Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). All studies had small sample sizes (9–25 participants), short durations (7–60 days), and predominantly included male participants, limiting generalizability. The specific form of red grape (e.g., grape seed extract) was used in all studies, but exact formulation details were not reported, so effects may not apply to whole grape or other extracts.
GSE decreased resting MAP (91 ± 2 vs. 88 ± 3) compared to the placebo (MAP: 89 ± 2 vs. 90 ± 2)
insulin, HOMA-IR, TC, TG, LDL-c, ALT, AST, AST/ALT, SBP, DBP and MAP decreased and QUICKi and HDL-c increased significantly (p-value for all < 0.05)
and MAP (NBW: 75±2 vs. 72±2 mmHg; obese: 86±3 vs. 84±3 mmHg)
GSE supplementation attenuated MAP at both workloads (40% VO2peak: 115 ± 1 vs. 112 ± 2 mmHg; 60% VO2peak: 126 ± 2 vs. 123 ± 2 mmHg)
Compared with PL, GSE supplementation significantly decreased MAP at rest (85 ± 3 mmHg vs. 82 ± 3 mmHg), 40% (102 ± 3 mmHg vs. 99 ± 3 mmHg), and 60% workloads (109 ± 3 mmHg vs. 107 ± 3 mmHg) (P = 0.001, ES = 0.2).