Foods rich in cocoa appear to reduce blood pressure but drinking tea may not

Apr 10 2007

Foods rich in cocoa appear to reduce blood pressure but drinking tea may not, according to an analysis of previously published research in the April 9 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

Current guidelines advise individuals with hypertension (high blood pressure) to eat more fruits and vegetables, according to background information in the article. Compounds known as polyphenols or flavonoids in fruits and vegetables are thought to contribute to their beneficial effects on blood pressure and cardiovascular risk. "Tea and cocoa products account for the major proportion of total polyphenol intake in Western countries," the authors write. "However, cocoa and tea are currently not implemented in cardioprotective or anti-hypertensive dietary advice, although both have been associated with lower incidences of cardiovascular events."

Dirk Taubert, M.D., Ph.D., and colleagues at the University Hospital of Cologne, Germany, conducted a meta-analysis of 10 previously published trials, five of cocoa's effects on blood pressure and five involving tea. All results were published between 1966 and 2006, involved at least 10 adults and lasted a minimum of seven days. The studies were either randomized trials, in which some participants were randomly assigned to cocoa or tea groups and some to control groups, or used a crossover design, in which participants' blood pressure was assessed before and after consuming cocoa products or tea.

The five cocoa studies involved 173 participants, including 87 assigned to consume cocoa and 86 controls, 34 percent of whom had hypertension (high blood pressure). They were followed for a median (middle) duration of two weeks. Four of the five trials reported a reduction in both systolic (the top number, when the heart contracts) and diastolic (the bottom number, when the heart relaxes) blood pressure. Compared with those who were not consuming cocoa, systolic blood pressure was an average of 4.7 millimeters of mercury lower and diastolic blood pressure was an average of 2.8 millimeters of mercury lower.

The effects are comparable to those achieved with blood pressure-lowering medications, the authors note. "At the population level, a reduction of 4 to 5 millimeters of mercury in systolic blood pressure and 2 to 3 millimeters of mercury in diastolic blood pressure would be expected to substantially reduce the risk of stroke (by about 20 percent), coronary heart disease (by 10 percent) and all-cause mortality (by 8 percent)," they write.

Of the 343 individuals in the five tea studies, 171 drank tea and 172 served as controls, for a median duration of four weeks. Drinking tea was not associated with a reduction in blood pressure in any of the trials.

Tea and cocoa are both rich in polyphenols, but while black and green tea contain more compounds known as flavan-3-ols, cocoa contains more of another type of polyphenol, procyanids. "This suggests that the different plant phenols must be differentiated with respect to their blood pressure-lowering potential and thus cardiovascular disease prevention, supposing that the tea phenols are less active than cocoa phenols," the authors write.

The findings do not indicate a widespread recommendation for higher cocoa intake to decrease blood pressure, but it appears reasonable to substitute phenol-rich cocoa products such as dark chocolate for other high-calorie or high-fat desserts or dairy products, they continue. "We believe that any dietary advice must account for the high sugar, fat and calorie intake with most cocoa products," the authors conclude. "Rationally applied, cocoa products might be considered part of dietary approaches to lower hypertension risk."