Across 4 studies, 2 reported beneficial small effects and 2 reported neutral small effects on systolic blood pressure. The beneficial findings come from a systematic review and an RCT in NAFLD patients, while a short-term RCT and a meta-analysis showed no significant effect. The median study duration was 34 days (range 7–60 days), and the most common dose was 520 mg/day of grape seed extract.
Caveats: Evidence base is small (only 4 studies) — conclusions should be considered preliminary. Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. The beneficial meta-analysis showed high heterogeneity (I² = 97.4%) and no significant pooled effect, indicating inconsistency across trials.
There were no differences on the SBP … between placebo and GSE treatments
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)
Intervention with grape seed extract may reduce systolic and diastolic blood pressure in subjects with hypertension or metabolic syndrome.
no significant effects on ... SBP (WMD: -3.55 mmHg, 95% CI: -7.59 to 0.49, I² = 97.4%)