Nibble of chocolate may lower blood pressure
levels and lead to clinically important reductions for
cardiovascular diseases, suggests a new study.
Results of the randomised, controlled, parallel-group trial, published in the Archives of Internal Medicine, involved 44 adults with pre- (BP 130/85 - 139/89) or stage one hypertension (BP 140/90 - 160/100), suggest that a daily serving of dark chocolate containing 30 calories associated with a lowering of blood pressure. Hypertension, defined as having a systolic and diastolic BP greater than 140 and 90 mmHg, affects about 600 million people worldwide and is associated with over seven million deaths. "The most intriguing finding of this study is that small amounts of commercial cocoa confectionary convey a similar BP-lowering potential compared with comprehensive dietary modifications that have proven efficacy to reduce cardiovascular event rate," wrote lead author Dirk Taubert from University Hospital of Cologne. "Whereas long-term adherence to complex behavioural changes is often low and requires continuous counselling, adoption of small amounts of flavanol-rich cocoa into the habitual diet is a dietary modification that is easy to adhere to and therefore may be a promising behavioural approach to lower blood pressure in individuals with above-optimal blood pressure," he added. The researchers randomly assigned the volunteers to a daily either portion of 6.3 g (30 kcal) of dark chocolate containing 30 mg of polyphenols (Ritter Sport Halbbitter, Alfred Ritter) or matching polyphenol-free white chocolate (Milka Weisse Schokolade, Kraft Foods) for 18 weeks. At the end of the study, the researchers observed that consumption of the dark chocolate led to reductions in both systolic and diastolic BP by 2.9 and 1.9 mm Hg, respectively, without affecting body weight, blood lipid levels, or blood sugar (glucose) levels). "Although the magnitude of the BP reduction was small, the effects are clinically noteworthy," wrote the researchers. "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 eight per cent, of coronary artery disease mortality by five per cent, and of all-cause mortality by four per cent. "Furthermore, the blood pressure reductions in our randomized trial are in the same range that were reportedly associated with habitual cocoa intake (a median of 4.2 g per day) in an epidemiological study involving elderly men." No change in blood pressure was observed as a result of eating the polyphenol-free white chocolate. The prevalence of hypertension in the population declined from 86 to 68 per cent. Consumption of the polyphenol-rich dark chocolate led to measurable increases in blood polyphenol concentrations, and the blood pressure reduction was accompanied by a sustained increase of S-nitrosoglutathione, linking the effects to nitric oxide production in the cardiovascular system. "The apparent mechanism by which dark chocolate lowered BP suggests a chronic increase in the production of nitric oxide in the vascular endothelium. The unstable nitric oxide reacts with thiol groups to form stable S-nitrosothiols that have been suggested to contribute to BP regulation," said the researchers. "Future studies should evaluate the effects of dark chocolate in other populations and evaluate long-term outcomes," the authors conclude. The British Heart Foundation's nutritionist Sara Stanner told the BBC: "It is important to remember that chocolate is also high in fat and calories so over-indulgence is not good for your heart. "Fruits and vegetables provide a range of polyphenols, as well as important vitamins and minerals. Eating five or more portions of fruit and vegetables a day is therefore the best way to protect your heart - and you don't need to worry about over-indulging." The study was funded by the University Hospital of Cologne, Germany Source: Journal of American Medical Association 2007, Volume 298, Number 1, Pages 49-60 "Effects of Low Habitual Cocoa Intake on Blood Pressure and Bioactive Nitric Oxide - A Randomized Controlled Trial" Authors: D. Taubert, R. Roesen, C. Lehmann, N. Jung, E. Schomig