Dietary polyphenols, such as those from grape products, may exert beneficial effects on cardiovascular health, including anti-hypertensive effects. We investigated the effect of a specific grape seed extract (GSE) rich in low-molecular-weight polyphenolic compounds on ambulatory blood pressure (ABP) in untreated subjects with pre- and stage I hypertension. In addition, potential mechanisms that could underlie the hypothesised effect of GSE on blood pressure (BP), and platelet aggregation, were explored. The study was designed as a double-blind, placebo-controlled, randomised, parallel-group intervention study including seventy healthy subjects with systolic BP between 120 and 159 mmHg. A 1-week run-in period was followed by an 8-week intervention period, during which subjects consumed capsules containing either 300 mg/d of GSE or a placebo (microcrystalline cellulose). Before and after the intervention, daytime ABP readings, 24 h urine samples and fasting and non-fasting blood samples were taken VSports手机版. The mean baseline systolic BP was 135. 8 (SE 1. 3) mmHg and diastolic BP was 81. 5 (SE 0. 9) mmHg. BP values were modestly, but not significantly, affected by the polyphenol-rich GSE treatment v. placebo with an effect of - 3. 0 mmHg for systolic BP (95% CI - 6. 5, 0. 5) and - 1. 4 mmHg for diastolic BP (95% CI - 3. 5, 0. 6). Vasoactive markers including endothelin-1, NO metabolites and asymmetric dimethylarginine, plasma renin activity and platelet aggregation were not affected by the GSE intervention. Our findings show that consumption of polyphenol-rich GSE does not significantly lower ABP in untreated subjects with pre- and stage I hypertension. .