Blood Pressure Lowering Effects of Grape Juice

• Blood pressure measured by 24-hour recorder [ Time Frame: 8 weeks ] [ Designated as safety issue: No ]
  

• Pulse wave velocity [ Time Frame: 8 weeks ] [ Designated as safety issue: No ]
  
• Pulse amplitude tonometry [ Time Frame: 8 weeks ] [ Designated as safety issue: No ]
  
• Blood pressure during mental tasks [ Time Frame: 8 weeks ] [ Designated as safety issue: No ]
  

Dietary Supplement: Concord Grape Juice
Approximately 16 oz of grape juice or placebo

Elevated blood pressure (BP) is among the most common and important risk factors for atherosclerosis. A number of non-pharmacological therapies have successfully been applied to prevent the development of elevated BP or reduce elevated BP. For example the DASH Study showed that a diet rich in fruits, vegetables and low fat dairy products, and reduced in saturated fat, total fat and cholesterol, substantially lowered blood pressure in normotensive and hypertensive individuals.

Within the past three years a number of small clinical trials have suggested suggest that drinking purple grape juice for a period of 6-12 weeks may lower blood pressure individuals with elevated blood pressure. Other clinical trials have shown that Concord grape juice improves the function of the vascular endothelium, possibly providing an explanation for the beneficial effect. However, there is a need for a prospective, controlled study to determine whether grape juice has a beneficial effect on blood pressure.

The present study will compare the effect of drinking Concord purple grape juice (7 ml/kg or about 16 oz/day for a 70 kg person) and the effect of calorie-matched placebo on 24-hour ambulatory blood pressure, blood pressure reactivity, and vascular function in men and women in the category of "pre-hypertension" (defined as blood pressure greater than 120/80, but less than 149/89 mmHg and Stage 1 hypertension (defined as blood pressure greater than 140/90, but less than 160/100). This study will specifically recruit patients with systolic blood pressure of 130-159 mmHg or diastolic blood pressure of 85-99 mmHg. The study will be double blind and have a crossover design with the order of treatment randomized (grape juice first or placebo first). A dietician will provide all subjects with formal instruction in a low salt diet, which is the current recommended initial therapy for patients with Stage 1 hypertension.

After a 1-week run-in period, subjects will consume each beverage for 8 weeks with a 4-week rest period between treatments. Blood pressure will be measured before and after each treatment period using a 24-hour ambulatory blood pressure recording. After each treatment period, we will measure changes in blood pressure induced by psychological challenge (mental arithmetic and computer tasks) and by the cold pressor test. In order to gain insight into the potential mechanisms of benefit, we will also examine the effects of beverage consumption on endothelial function, stiffness of the central aorta, fasting glucose and insulin, body weight, and markers of systemic inflammation, including CD40 ligand and C-reactive protein. Finally, we will store plasma samples for future investigation of other potential effects of grape juice on the cardiovascular system.

We hypothesize that Concord grape juice will have favorable effects on blood pressure compared to placebo.