Dietary polyphenols derived from fruits and vegetables have been shown to lower blood pressure (BP) in both normotensive and hypertensive subjects. The current study was designed to investigate the effects of a grape seed extract (GSE) on BP, and the mechanisms underlying the putative BP lowering effect of polyphenols. The GSE was characterized by a very high (∼90%) total polyphenol content with particularly low molecular weights.
Seventy untreated subjects with elevated BP levels (54% male; mean age 64 and daytime ambulatory SBP/DBP 136/82 mmHg) were included in this double-blind placebo-controlled, randomized parallel group study. After a run-in period of one week, the subjects consumed each day a capsule with GSE (MegaNatural®-BP, 300 mg per day) or a placebo capsule, during 8 weeks. Ambulatory BP was measured on 2 separate days for 12 hours (daytime; at 20 min intervals) at baseline and at end of intervention. Blood and urine were collected to measure mechanistic markers.
Daytime ambulatory SBP/DBP decreased (-4.6/-2.1 mmHg) compared to baseline values, but these changes were not significantly different from the control group (-3.1/-1.4 mmHg, p > 0.1). Renin activity, endothelin-1 and NOx concentrations were similar in both study arms.
Consumption of high polyphenol grape seed extract does not lower BP significantly compared to placebo in untreated borderline hypertensive subjects.