Dr. C. Tissa Kappagoda and co-investigators at the University of California, Davis, studied 24 men and women who met the criteria for metabolic syndrome set by the Adult Treatment Panel of the National Cholesterol Education Program. "They weren't chosen for high blood pressure, per se," Dr. Kappagoda told Reuters Health.
The subjects were randomized into one of three treatment arms: one group received 150 mg grape seed extract daily, a second received 300 mg daily and a third received placebo.
Parameters of the metabolic syndrome were measured at baseline and at the end of the 4-week study period. These included blood glucose, plasma insulin and insulin resistance, serum lipids and oxidized low-density lipoprotein cholesterol. Blood pressure was measured using an ambulatory blood pressure monitoring device over a 12-hour period. Platelet aggregation and activation were also evaluated at the beginning and end of the study.
Baseline blood pressures ranged from 120-130 mm Hg systolic and below 80 mm Hg diastolic. After four weeks of treatment, subjects receiving grape seed extract had a drop in systolic blood pressure of approximately 12 mm Hg and in diastolic blood pressure of approximately 9 mm Hg, Dr. Kappagoda told Reuters Health.
Perhaps more significant was the change in oxidized LDL, he added. "The higher the oxidized LDL at baseline, the greater the drop in blood pressure," he said.
Polyphenolic compounds, derived from gallic acid in grape seed extract, cause a release in nitric oxide, which in turn results in an endothelium-dependent relaxation, Dr. Kappagoda explained. "These compounds are found in brightly colored fruits and vegetables," he pointed out. While the effects were statistically significant, "we are not suggesting this is a treatment for hypertension."