Credit of photo: VOA

It is not news that eating dark chocolate may lower blood pressure (BP) in some people as many small and short-term studies have found.   But a new study published in the July 4 2007 issue of the Journal of the American Medical Association found that to have a small blood pressure lowering effect, you may only need a tiny piece of dark chocolate daily for a couple of weeks, if you are healthy.

The study led by Dirk Taubert, M.D., Ph.D., of University Hospital of Cologne, Germany, and colleagues, who have studied cocoa rich food for quite some years, found eating no more than 30 calories a day of dark chocolate was associated with a lowering of blood pressure in healthy subjects who had high blood pressure but in normal ranges.

Previous studies have shown high consumption of cocoa-rich foods such as dark chocolate can lower blood pressure and researchers believe that is due probably to the action of the cocoa polyphenols such as flavanols.  

One study reported in 2005 by Davide Grassi and colleagues at University of L'Aquila, L'Aquila, Italy shows that high intake of dark chocolate lowers systolic blood pressure.   The 15-day study involved 15 healthy people who ate 100 grams of dark chocolate a day.   The authors suggested that the benefit may be due to the antioxidant properties of flavanols and the increased bioavailability of nitric oxide.

A similar study of 20 men and women with high blood pressure, but not on blood pressure medications found eating three ounces of dark chocolate a day for two weeks significantly reduced their blood pressure by an average of 10 percent. Specifically, patients who ate dark chocolate experienced an average 11.9 mm Hg drop in their systolic blood pressure and an 8.5 mm Hg drop in diastolic blood pressure.   The study was conducted by Dr. Jeffrey B. Blumberg and colleagues at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and published in the July 18 2005 online edition of Hypertension.

The blood pressure lowering effect of high intake of dark chocolate is not always seen in every previous study though. A two-week small trial by Engler M. B. from University of California, San Francisco and colleagues shows daily high intake of dark chocolate with 213 mg pocyanidins and 46 mg epicatechin or intake of low-flavonoid dark chocolate bars (46 grams) did not change blood pressure in 21 healthy subjects although the high flavonoid chocolate bars did improve endothelium-dependent flow-mediated dilation of the brachial artery.   The study was published in the June 23 2004 issue of Journal of the American College of Nutrition.

Many studies that found consumption of dark chocolate is associated with reduced blood pressure lasted only two weeks or less.   Long term consumption of high amounts of chocolate may become an issue as it contains high sugar, fat and calorie intake, which could offset the beneficial effects of vascular health.   In the current study, the German researchers wanted to know if low daily intake of dark chocolate would have a blood pressure lowering effect.

In the study, Dirk Taubert and colleagues enlisted 44 healthy adults aged 56 to 73 with untreated upper-range pre-hypertension or stage 1 hypertension.   The participants were randomly assigned 6.3 grams or 30 calories a day of dark chocolate containing 30 mg polyphenols or white chocolate without polyphenols.

They found after 18 weeks, those who ate dark chocolate had their systolic blood pressure reduced by −2.9 (1.6) mm Hg and diastolic BP by −1.9 (1.0) mm Hg without changes in body weight, plasma levels of lipids or glucose.   The hypertension prevalence declined from 86 to 68 percent.   These dark chocolate eaters had cocoa phenols and increased vasodilatory S-nitrosoglutathione in their blood.  

In contrast, the blood pressure, both systolic and diastolic, remained unchanged throughout the study in those who ate white chocolate.    Biomarkers also remained the same in the group.

The results suggest that polyphenols from cocoa and nitric oxide may be involved in the blood pressure lowering effect and tiny amounts of dark chocolate is effective in lowering blood pressure in healthy people.

“Although the magnitude of the BP reduction was small, the effects are clinically noteworthy. On a population basis, it has been estimated that a 3-mm Hg reduction in systolic BP would reduce the relative risk of stroke mortality by 8 percent, of coronary artery disease mortality by 5 percent, and of all-cause mortality by 4 percent,” the authors wrote.

The reduction of mortality by consuming flavanols-loaded dark chocolate is not just speculation of the German researchers.  Through at least partially the blood lowering mechanism, the mortality from coronary heart disease and stroke may be reduced by as much as 19 percent in those who ate the highest amounts of cocoa rich foods, compared to those who ate the lowest amounts, according to Ding E L. and colleagues from Department of Epidemiology at Harvard University School of Public Health.

Ding’s estimation of mortality reduction associated with consumption of cocoa rich food was based on a review of 139 publications on cocoa-rich food.   Ding and colleagues wrote in the Jan. 2006 issue of Nutrition & metabolism "The body of short-term randomized feeding trials suggests cocoa and chocolate may exert beneficial effects on cardiovascular risk via effects on lowering blood pressure, anti-inflammation, anti-platelet function, higher HDL, decreased LDL oxidation.”

The significant part of the current study is that a small piece of dark chocolate can have a big effect on blood pressure.   Taubert and colleagues concluded "Data in this relatively small sample of otherwise healthy individuals with above-optimal BP indicate that inclusion of small amounts of polyphenol-rich dark chocolate as part of a usual diet efficiently reduced BP and improved formation of vasodilative nitric oxide."

A scientist affiliated with foodconsumer.org suggests that although dark chocolate can be part of a healthy diet, consumers should never overuse it.  Research is still needed to confirm the long term effect of dark chocolate on blood pressure.

Vol. 298 No. 1, July 4, 2007      JAMA  

Effects of Low Habitual Cocoa Intake on Blood Pressure and Bioactive Nitric Oxide, A Randomized Controlled Trial

Dirk Taubert, MD, PhD; Renate Roesen, PhD; Clara Lehmann, MD; Norma Jung, MD; Edgar Schömig, MD

JAMA. 2007;298:49-60.