Tuesday, July 3, 2007

Dark Chocolate and Blood-Pressure Reduction

A piece of dark chocolate a day keeps the doctor away

July 3, 2007

When it comes to dark chocolate and blood-pressure reduction, it would seem that a little goes a long way. A new randomized controlled study has shown that just one square of dark chocolate a day reduces blood pressure by a few mm Hg in healthy people with above-optimum blood pressure.

Dr Dirk Taubert (University Hospital of Cologne, Germany) and colleagues report their findings in the July 4, 2007 issue of the Journal of the American Medical Association.

Taubert told heartwire that this is the first research to show the benefits of cocoa in dark chocolate long-term—the study lasted 18 weeks. They were also able to demonstrate a feasible mechanism for the BP-lowering effects of dark chocolate, he noted.

Hypertension expert Dr Franz H Messerli (Columbia University, New York), who was not involved in this research, told heartwire: "This is now study 6 showing the same phenomenon. It is an exceedingly well-done, very thorough study, which I think is nothing short of revolutionary."

Dark chocolate increases production of nitric oxide

Taubert et al say that short-term studies have previously shown that high doses of cocoa for two weeks can improve endothelial function and reduce blood pressure, due to the action of cocoa polyphenols. "But the clinical effect of low habitual cocoa intake on BP and the underlying BP-lowering mechanisms are unclear."

They conducted arandomized, controlled, investigator-blinded, parallel-group trialwith 44 adults, aged 56 to 73, with untreated upper-range prehypertension or stage 1 hypertension without concomitant risk factors. The participants were randomly assigned to receive either one square (6.3 g) of a commercial brand of dark chocolate per day, constituting just 30 kcal, or matching polyphenol-free white chocolate for 18 weeks.

The primary outcome measure was change in BP after 18 weeks. Secondary outcomes included changes in plasma markers of vasodilative nitric oxide (S-nitrosoglutathione) and oxidative stress (8-isoprostane) and bioavailability of cocoa polyphenols.

From baseline to 18 weeks, dark-chocolate intake reduced mean systolic BP by 2.9 mm Hg (p<0.001)>

The BP decline was accompanied by a sustained increase of S-nitrosoglutathione by 0.23 nmol/L (p<0.001)white chocolate caused no changes in BP or plasma biomarkers.

"The apparent mechanisms by which dark chocolate lowered BP suggests a chronic increase in the production of nitric oxide in the vascular endothelium," the researchers explain. "It is likely that cocoa flavanols in dark chocolate were responsible for the observed effects on S-nitrosoglutathione and BP."

Long-term RCTs with larger numbers of participants needed.

"This study provides enough evidence to suggest that low amounts of polyphenol-rich dark chocolate as an addition to a healthy diet caused progressive reductions of systolic and diastolic BP in older subjects with prehypertension without inducing weight gain or other adverse effects," Taubert said.

However, he says the findings need to be replicated in other populations (their participants were predominantly white, older, and mildly hypertensive) and that the effects of dark chocolate need to be evaluated in long-term randomized controlled studies with larger numbers of participants.

"A few hundred patients would be needed, with a follow-up of at least one year," he says.

"However, we are more interested in the mechanism, and we are trying to find out which polyphenol in the cocoa is responsible. When we know the substance, we will go back and test it."

Small changes in BP, but big implications

Messerli says the clinical significance of these apparently small changes in blood pressure is nevertheless extremely important. "When you look at this populationwise, there's no question that this achieves a major reduction in heart attacks and stroke."

But he cautions that people must understand that the chocolate has to be dark. "Regular (milk) or white chocolate has no benefit whatsoever. It is completely useless. I now tell my patients, I will take away your Häagen-Dazs and your crème brûlée, but I give you a little bit of dark chocolate. There are no adverse events, in contrast to many BP-lowering pills, and patients are motivated to enjoy a daily treat."

He also points out that the amount of dark chocolate eaten is key, because people still need to keep within their daily limit of calories. The one square in this study was 6.3 g and represented only 30 kcal per day, he notes, "but previous studies have shown that 100 g of dark chocolate lowers BP by 12/8 mm Hg; however, this is somewhat of a Pandora's box."

Taubert D, Roesen R, Lehmann C, et al. Effects of low habitual cocoa intake on blood pressure and bioactive nitric oxide. A randomized controlled trial. JAMA 2007; 298:49-60

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