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Dark Chocolate Reduces Blood Pressure and Improves Insulin Resistance

Jul 26, 2005

If you have high blood pressure, a daily bar-sized serving of flavonol-rich dark chocolate might lower your blood pressure and improve insulin resistance. “Previous studies suggest flavonoid-rich foods, including fruits, vegetables, tea, red wine and chocolate, might offer cardiovascular benefits, but this is one of the first clinical trials to look specifically at dark chocolate’s effect on lowering blood pressure among people with hypertension,” said study author Jeffrey B. Blumberg, Ph.D.

Blumberg is a senior scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. Flavonoids are natural antioxidants found in many foods from plants.


“This study is not about eating more chocolate,” Blumberg cautioned. “It suggests that cocoa flavonoids appear to have benefits on vascular function and glucose sensitivity.”

Blumberg and colleagues at the University of L’Aquila in Italy, including senior author Dr. Claudio Ferri, studied 10 men and 10 women. They all had hypertension and a systolic blood pressure (the top number in a blood pressure reading) between 140 and 159 millimeters of mercury (mm Hg) and a diastolic blood pressure (bottom number) between 90 and 99. None of the participants was taking antihypertensive medicines, and none had diabetes or other disease, nor did they smoke.

For one week before starting the study, participants avoided all chocolate and other flavonoid-rich foods. During the next 15 days, half ate a daily 3.5-ounce bar of flavonoid-rich dark chocolate, while the other half ate the same amount of white chocolate. After another week of avoiding flavonoid-rich foods, each subject “crossed over” and ate the other chocolate.

“White chocolate, which has no flavonoids, was the perfect control food because it contains all the other ingredients and calories found in dark chocolate,” Blumberg said. “It’s important to note that the dark chocolate we used had a high level of flavonoids, giving it a slightly bittersweet taste. Most Americans eat milk chocolate, which has a low amount of these compounds.”

The researchers found a 12 mm Hg decrease in systolic blood pressure and a 9 mm Hg decrease in diastolic blood pressure in the dark chocolate group after 15 days. Blood pressure did not decrease in the white chocolate group.

“This is not only a statistically significant effect, but it’s also a clinically meaningful decline,” Blumberg said. “This is the kind of reduction in blood pressure often found with other healthful dietary interventions.”

The researchers report that the dark chocolate group also experienced a significant reduction in several measures of insulin resistance compared to the white chocolate group. Levels of LDL (“bad”) cholesterol dropped by about 10 percent in the dark chocolate group, but stayed the same in the white chocolate group.

“The findings do not suggest that people with high blood pressure should eat lots of dark chocolate in lieu of other important blood pressure-reduction methods, such as medication and exercise,” Blumberg said. “Rather, we are identifying specific flavonoids that can have a benefit on blood pressure and insulin sensitivity.”

He said these results can generate improved dietary recommendations that will help people regulate these risk factors. Blumberg said flavonoid-rich foods should be part of an overall healthy diet, and that some dark chocolate could be part of that effort, as well as fruits, vegetables, and whole grains.

“We should also look at patients with other forms of hypertension, as well as people who have coronary artery disease, type 2 diabetes or a high-normal blood glucose level.”

Reported in Hypertension:July 18. 2005 Journal of the American Heart Association.