Dark chocolate shown to have a cardiovascular benefit in hypertensive patients

July 18, 2005

L'Aquila, Italy - Well timed with the movie opening of Charlie and the Chocolate Factory this weekend, the benefits of chocolate received an additional boost with findings from a small study suggesting that the consumption of dark chocolate provides a cardiovascular benefit if included as part of a healthy diet for patients with essential hypertension[1]. Eating 100 g of dark chocolate for two weeks reduced blood pressure and LDL cholesterol levels, improved flow-mediated dilation, and ameliorated insulin resistance in this group of patients with hypertension, report investigators.

The results of the study are published online July 19, 2005 in Hypertension.

Benefit of cocoa likely due to flavanols

Commenting on the study for heartwire , senior investigator Dr Claudio Ferri (University of L'Aquila, Italy) explained that the consumption of flavanol-rich products, particularly dark chocolate, has already been shown to increase endothelium-dependent vasodilation in healthy subjects and to decrease blood pressure in hypertensive elderly patients and healthy volunteers. Other studies have also shown that dark chocolate, at least in healthy subjects, decreased insulin resistance.

The present study was designed to expand on the previous data in healthy volunteers and investigate the effects of dark chocolate on other parameters, including ambulatory blood-pressure measurement, flow-mediated dilation of the brachial artery, and insulin sensitivity in patients with essential hypertension. Twenty never-treated patients with essential hypertension10 males and 10 femaleswere included in the study. Patients were aged 25 to 60 years with a systolic blood pressure between 140 to 159 mm Hg and a diastolic blood pressure between 90 and 99 mm Hg.

After a seven-day chocolate-free run-in, patients were randomized to receive either 100 g of dark chocolate daily, containing 88-mg flavanols, or 90 g of flavanol-free white chocolate. Caloric intake was equivalent in both treatment arms. After a second seven-day chocolate-free period, patients were crossed over to the other treatment. Fifteen subjects were recruited and served as a normotensive control group.

Consumption of the dark chocolate, but not white chocolate, significantly decreased both systolic and diastolic ambulatory blood-pressure measurements, with both systolic and diastolic blood pressures decreasing during daytime and nighttime. Serum LDL-cholesterol levels also declined in the patients randomized to dark chocolate, whereas white chocolate had no effect on either total- or LDL-cholesterol levels.

Cholesterol and blood pressure values at baseline and after 15 days of dark-chocolate and white-chocolate consumption

Characteristic Dark chocolate before (n=10) Dark chocolate after (n=10) White chocolate before (n=10) White chocolate after (n=10)
Total cholesterol (mmol/L) 5.4 5.0* 5.4 5.4
LDL cholesterol (mmol/L) 3.4 3.0 3.4 3.4
24-hour systolic blood pressure (ambulatory blood pressure monitoring) (mm Hg) 135.5 123.6 135.6 134.7
24-hour diastolic blood-pressure (ambulatory blood-pressure monitoring) (mm Hg) 88.0 79.6 87.6 87.5
*p=0.0003 dark-chocolate vs baseline and white-chocolate values
p<0.05 dark-chocolate vs baseline and white-chocolate values
p<0.0001 dark-chocolate vs baseline and white-chocolate values

The researchers report that the dark-chocolate group also experienced a significant reduction in several measures of insulin resistance compared with the white-chocolate group. Compared with baseline, dark-chocolate consumption lowered insulin resistance, as measured by homeostasis model assessment (HOMA) scores, and raised the quantitative insulin-sensitivity check index (QUICKI) and the insulin-sensitivity index (ISI). Flow-mediated vasodilation, impaired in the hypertensive patients compared with a control group, increased to almost normal levels after consumption of dark chocolate.

"The benefits from cocoa are likely to depend on flavanols, a family of flavanoids also contained in tea, red wine, and other vegetables but particularly present in cocoa beans, tea, and red wine," said Ferri. "Why are flavanols and flavonoids beneficial? We truly do not know, but the most likely explanation is represented by the positive effect of flavanols and flavonoids on nitric oxide."

Ferri said that the magnitude of blood-pressure reduction was "somewhat surprising" but noted that the study protocol called for careful attention to daily caloric intake, with the normal diet of participants slightly modified to prevent fluctuations in body weight. As a result, investigators cannot fully exclude a certain confounding role of other dietary changes.

Larger controlled trials, with longer follow-up, are still needed, said Ferri, adding that it is important for patients to remain slim and not pack on the pounds thinking they're doing their heart good by eating excessive amounts of dark chocolate. He said that moderation remains an important message for patients and does not recommend any Willie Wonka-like chocolate splurges.

"When you say to people, 'Drink red wine,' you obviously mean drink one to two glasses of red wine daily and absolutely no more," said Ferri. "With cocoa it is the same, since obesity is our true mortal enemy. Thus, I do not want to tell people: eat cocoa and be glad! Indeed, I know that you can eat some cocoa—very, very small amounts—and probably derive some cardiovascular benefit from this."

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