Effects of vitamin C and grape-seed polyphenols on blood pressure in treated hypertensive individuals

Following a 3‐week run‐in period (during which tea and coffee intake was limited to 3 cups per day and all red wine was ceased), subjects were allocated to a study treatment via block randomization using computer‐generated random numbers, devised by the statistician. Volunteers were assigned to receive either (1) 500 mg/day vitamin C and matched grape‐seed polyphenol placebo, (2) 1000 mg/day grape‐seed polyphenols and matched vitamin C placebo, (3) 500 mg/day vitamin C and 1000 mg/day grape‐seed polyphenols, or (4) matched placebo tablets for both grape‐seed polyphenols and vitamin C. Participants took assigned tablets during a 6 week intervention period in a double‐blind fashion. Tablets were taken twice daily at meal times as 250 mg and 500 mg of vitamin C and polyphenols, respectively. All tablets were identical in appearance, size. All study personnel and participants were blinded to treatment assignment for the duration of the study. Outcome measurements were performed at the end of the run‐in period (baseline) and again at the end of the 6 week intervention period. Blood pressure Blood pressure was assessed as 24 h ambulatory blood pressure with blood pressure and heart rate measured every 20 min during the day time and every 30 min at night time. Ambulatory blood pressurewas assessed by a trained researcher who fitted a Spacelabs monitor (Spacelabs Medical Inc. Redmond, WA, USA) and explained its use to the participants. The monitor was fitted to the non‐dominant arm approximately 2.5 cm above the antecubital fossa. Participants were instructed to continue their usual daily activities and to avoid any vigorous exercise. Measurements showing an error code or those with a pulse pressure of less than 20 mm Hg were excluded from the analysis. Blood pressure traces were considered complete if more than 80% of the recordings were valid. Rate of blood pressure variation Within‐visit rate of variation of systolic and diastolic blood pressure, pulse pressure and heart rate were calculated for day time (08:00–20:00) and night time (22:00‐06:00) periods from the 24 h ambulatory blood pressure traces. The within‐visit rate of measurement‐to‐measurement blood pressure and heart rate variation was calculated using the slope of the change in systolic blood pressure, diastolic blood pressure, pulse pressure and heart rate between each reading over time.