A new German study suggests that eating a small amount of dark chocolate every day could lower blood pressure without increasing weight or other health risks.
The study is published in today’s issue of the Journal of the American Medical Association (JAMA).
Other studies have already suggested that eating large amounts of foods rich in cocoa can lower blood pressure. This is thought to be because of the polyphenols in the cocoa, a group of beleficial plant chemicals that includes flavanols.
However, eating large amounts of cocoa often increases other risk factors because of the higher intake of sugar, fat and calories. So the researchers, who are based at the University Hospital of Cologne, thought they would test the effects of a small daily portion of polyphenol-rich cocoa on blood pressure, since this should not increase the other risks.
The researchers recruited 44 adults aged from 56 to 73, comprising 24 women and 20 men, who had untreated upper range prehypertension (blood pressure ranging from 130/85 to 139/89) or stage 1 hypertension (140/90 to 160/100) to take part in the trial which lasted from January 2005 to December 2006. They had no other associated risk factors. All participants were attending one primary care clinic in Germany.
The participants were randomly assigned to take 6.3 g (30 calories) per day of dark chocolate (about the size of a Hershey’s Kiss) containing 30 mg of polyphenols, or a matching dose of white chocolate that did not contain polyphenols for 18 weeks.
The results showed that:
- Eating dark chocolate for 18 weeks reduced average systolic blood pressure (the top reading) by 2.9 mm of mercury.
- It also reduced the average diastolic blood pressure by 1.9 mm of mercury.
- These reductions were not accompanied by changes in body weight, plasma levels of lipids or glucose.
- The proportion of participants with hypertension who ate dark chocolate went down from 86 to 68 per cent.
- The dark chocolate group also had increased levels of plasma biomarkers: cocoa phenols and vasodilatory S-nitrosoglutathione.
- The systolic and diastolic blood pressure of the participants who ate white chocolate did not change.
S-nitrosoglutathione is a precursor of nitric oxide, a compound that causes relaxation and dilation of blood vessels and is linked to decreased blood pressure. It is used as a biomarker for vasodilative nitric oxide.
The researchers concluded that:
“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.”
Commenting on their findings they said that:
“Although the magnitude of the BP [blood pressure] 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.”
They added that the most interesting result was that small amounts of commercially available cocoa have a similar beneficial effect on blood pressure as comprehensive diet programmes that have been used to reduce cardiovascular risks.
But getting patients to stick to complex behaviour changes in the longer term is difficult and there is a high drop out rate with the more conventional complex dietary programmes, so perhaps the simple addition of 30 calories of dark chocolate a day, without any other changes, would be more effective at helping people with high blood pressure to reduce it.
Other scientists are not so sure, writing in various media reports yesterday. For instance, would people stop at such a small amount of chocolate every day? Is that not as difficult to stick to as trying to follow a diet sheet?
The authors said that more longer term studies are needed to evaluate the effects of dark chocolate in other, larger populations.
“Effects of Low Habitual Cocoa Intake on Blood Pressure and Bioactive Nitric Oxide: A Randomized Controlled Trial.”
Dirk Taubert, Renate Roesen, Clara Lehmann, Norma Jung, and Edgar Schömig.
JAMA. 2007;298:49-60.
Vol. 298 No. 1, July 4, 2007
Written by: Catharine Paddock
Writer: Medical News Today