Supplementing with 2 or 3 capsules of a standard grape seed extract supplement can lower systolic blood pressure by 8-11 points in mild hypertension. With a bit of luck, your blood pressure will then return to normal. This is according to a meta-analysis published in Medicine in 2016.

Study
Chinese researchers affiliated with Binzhou Medical University tracked 16 previously published trials in which participants received a daily supplement containing 100-2,000 milligrams of grape seed extract for 2-16 weeks. In all trials, the effect of supplementation on blood pressure was determined.

The researchers aggregated the trial results and reanalyzed them.

The main bioactive compounds in grape seed extract are oligomeric proanthocyanidins (OPCs) such as procyanidin C1 and procyanidin B2. These polyphenols activate the enzyme endothelial nitric oxide synthase in the blood vessel walls. This enzyme releases nitric oxide from arginine, making the blood vessel walls more flexible. Furthermore, OPCs inhibit endothelin-1, a peptide that constricts blood vessels.

Results
Overall, supplementation with grape seed extract reduced systole by 6 points and diastole by 3 points. These are moderate to small effects, respectively. Supplementation appeared particularly effective for people under fifty.

Supplementation also proved effective in people with mild hypertension. The researchers defined mild hypertension as high-normal blood pressure and grade 1 hypertension. This doesn't mean that supplementation has no effect on more severe hypertension - grade 2 and higher. Researchers simply didn't look at severe hypertension in the studies they used.

Click on the tables below for a larger version.

If you have healthy blood pressure, grape seed extract will not lower it. But for mild hypertension, supplementation can bring your blood pressure into the healthy range.

Moreover, supplementation was more effective if it lasted 8 weeks or longer - and if the daily dose remained below 800 milligrams. In the most convincing studies, researchers used doses of 150-300 milligrams of grape seed extract.

Conclusion
According to this meta-study, supplementation with grape seed extract can, under favorable conditions, lower systolic blood pressure by 8-11 points. This is roughly the effect of a low-dose ACE inhibitor.

A 10-point reduction in systolic blood pressure equates to a 20 percent reduction in the risk of stroke and a 15 percent reduction in the risk of vascular disease.