Written by: Ana Iturbides, Health Writer, Acupuncture Atlanta
The study conducted by Sivaprakasapillai and colleagues sought to examine the effect of grape seed extract on blood pressure in subjects with metabolic syndrome. The positive effects of grape seed extract have been demonstrated in several prior studies. The positive results are said to be a result of the presence of phenolic compounds that are commonly found in plant products (Sivaprakasapillai et al., 1). Phenolic compounds are derived from phenol, which is one of a series of acidic organic compounds (Medline Medical Dictionary). In particular, the phenolic compounds found in grapes have been linked to the French Paradox, which states that the French have a relatively small risk of coronary heart disease, despite a diet rich in red wine and saturated fats (CBS News, “The French Paradox”). The phenolic compounds found in grapes have shown to have a variety of positive effects on metabolic syndrome. Among them are the causing of endothelium-dependent relaxation of blood vessels and the activation of endothelial nitric oxide synthase (Sivaprakasapillai et al., 1). Endothelium-dependent relaxation is simply the relaxing of the flat cells that line internal body cavities, such as those in the heart. Once these cavities are relaxed, they allow for the opening of blood vessels. Endothelial nitric oxide synthase is important because it is the production and distribution of nitric oxide, which is an essential substance that acts to communicate within and between cells to regulate numerous processes in the body (MedLine Medical Dictionary).
Metabolic syndrome, according to the authors, was defined using the National Cholesterol Education Program Adult Treatment Panel. This panel defined the syndrome as consisting of at least three of the following factors: abdominal obesity, elevated serum triglycerides, low serum high-density lipoprotein (HDL) concentration, hypertension, and elevated blood glucose. All of the factors mentioned were associated with impaired blood vessel function because each factor often occurs alongside one or more factors to decrease oxygen and nitrogen production and distribution throughout the body (Sivaprakasapillai et al., 1).
Materials and Methods
The authors conducted the four-week long study on a sample of 27 adults ranging in age from 25-80. Every adult in the study had been diagnosed with metabolic syndrome. The parameters for exclusion from the study included clinical evidence or diagnosis of coronary artery, pulmonary, gastrointestinal, or renal disease and daily consumption of vitamins or prescription medication (Sivaprakasapillai et al., 2). The 27 subjects were randomized into three groups. One group received a placebo, a second group received 300 mg/d of grape seed extract, and a third group received 150 mg/d of grape seed extract. The grape seed extract given to two of the three groups contained 94% phenol.
The subjects’ blood pressure was tested with an ambulatory blood pressure device that recorded daytime blood pressure. Subjects were also advised to maintain their normal level of physical activity and diet. Food diaries were used to measure diet at the beginning and end of the study (Sivaprakasapillai et al., 2). At the end of the study, a final measurement of blood pressure was taken. Fasting samples were collected to measure hemoglobin, white cell count, serum lipids, serum glucose, insulin, and oxidized LDL. Additional samples were obtained from the placebo group and the 300 mg group (Sivaprakasapillai et al., 2). Oxidized LDL was measured using immunosorbent assay and plasma insulin was measured using human specific radioimmunoassay. The authors used an ANOVA statistical test to measure the efficacy of grape seed extract on blood pressure. The primary endpoints for analysis were systolic and diastolic blood pressure, and the secondary endpoints were the changes in serum lipids and oxidized LDL.
At the end of the four-week study period, systolic and diastolic blood pressure decreased in both groups that received grape seed extract. Systolic blood pressure is the highest arterial blood pressure of a cardiac cycle that occurs immediately after the contraction of the left heart ventricle. Diastolic blood pressure is the lowest arterial blood pressure of a cardiac cycle that occurs when the cavities in the heart dilate and fill with blood (MedLine Medical Dictionary). No change in metabolic syndrome was seen in the placebo group.
While the intervention groups did experience a decrease in systolic and diastolic blood pressure, no additional changes were seen in any of the three groups in regards to serum total, LDL, and HDL cholesterol.
Discussion and Conclusion
The authors’ findings indicate that doses of grape seed extract at 150 mg/d or 300 mg/d decreased both diastolic and systolic blood pressure in study subjects with metabolic syndrome as defined by the National Cholesterol Education Program Adult Treatment Panel (Sivaprakasapillai et al., 3). Based on these findings, the authors suggest that grape seed extract can be successful in decreasing blood pressure in adult subjects with metabolic syndrome.
Similar studies have concluded that grape seed extract did not cause a reduction in blood pressure, but the authors point out that those null findings may have been due to differences in the potency of the extract. As stated before, the extract that Sivaprakasapillai and colleagues used contained 94% phenolic compound, whereas other studies have used a less concentrated dose. Additionally, the authors found that a 300 mg/d dose of grape seed extract was found to have therapeutic effects on reducing oxidized LDL cholesterol when LDL concentrations were high. This is promising news since an increase in oxidized LDL is often seen as a precursor for the development of atherosclerosis (Sivaprakasapillai et al., 4).
Metabolic syndrome is becoming a serious public health problem, particularly throughout the Western world. It is an important risk factor for the development of coronary artery disease and diabetes. This study has been consistent with many of the relevant literature in demonstrating that grape seed extract can in fact work to decrease blood pressure in patients with metabolic syndrome.
 CBS News, “The French Paradox”. http://www.cbsnews.com/video/watch/?id=4750380n.
 Medline Plus Medical Dictionary. http://www.nlm.nih.gov/medlineplus/mplusdictionary.html.
 Sivaprakasapillai, B., Edirisinghe, I., Randolph, J., Steinberg, F., Kappagoda, T. “Effect of grape seed extract on blood pressure in subjects with the metabolic syndrome” Metabolism Clinical and Experimental 58 (2009);1743-1746.