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Dark Chocolate’s Heart-Health Secret Discovered
2/6/2006
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Studies confirm cardiovascular benefits of cocoa and the suspected reason for its protective power
by Craig Weatherby and Randy Hartnell


There’s little doubt that both unrefined cocoa powder and dark chocolates—those containing 60 percent or more cocoa—are good for heart health.

Thanks to a wealth of research in recent years, scientists believe, with a high degree of certainty, that unrefined cocoa and dark chocolate alike produce four effects beneficial to cardiovascular health, each of which are known to result when antioxidants neutralize free radicals in the blood:
  1. Keep arteries relaxed. Free radicals prompt the endothelial cells that line our arteries to send “contract, please” signals to surrounding muscle, thereby narrowing the artery and increasing the risk of heart attack.
  2. Reduce the risk of dangerous blood clots. Bone marrow cell fragments called blood platelets clump together in response to internal or external bleeding, to help form clots that can stem the flow. Free radicals increase the tendency of platelets to aggregate into clumps, while antioxidants and anti-inflammatory agents like aspirin and ginger reduce unhealthful clotting.
  3. Reduce oxidation of LDL cholesterol in the blood. This helps prevent it from adhering to artery walls and oxidizing other blood fats.
  4. Raise blood levels of HDL (“good”) cholesterol. HDL carries cholesterol back to the liver (where it was produced), to be passed from the body. HDL may also remove excess cholesterol from plaque in arteries. A high level of HDL (i.e., over 45 mg/dL) and a high ratio of HDL to total cholesterol reduces the risk of heart attacks.
But, until a specific compound in cocoa was shown to produce any of these effects, scientists could not attribute cocoa’s cardiovascular benefits to its polyphenol antioxidants with absolute certainty.

This information gap meant that people could not be directed to consume other foods or beverage containing the beneficial compound(s), nor could any be isolated for possible use as drug-like preventive agents.

Now, the results of a recent Harvard-run research project in Panama appear to have put any and all doubts to rest.

New study finds chocolate’s main heart hero
Now, findings from two well-designed research studies, reported just last month, provide very strong support for this hypothesis with regard to the artery-relaxing effects of cocoa.  Better yet, they identify the specific antioxidant polyphenol that does most of the heavy antioxidant lifting to protect heart health.

A research team led by Norman Hollenberg, M.D. Ph.D. of Harvard Medical School recruited volunteers among the Kuna Indians, who live on the San Blas islands off the coast of Panama. High blood pressure and other signs of cardiovascular disease are rare among the Kuna, who consume three to four cups of flavanol-rich cocoa every day.

And, previous studies carried out by Dr. Hollenberg's team found that Kuna who migrated to the mainland drink much less cocoa—only about four cups per week—and do not enjoy the same high level of cardiovascular health.

The new controlled clinical studies, which employed a randomized double-blind cross-over design—the most rigorous methodology possible—examined the effect of four different drinks on vascular (blood vessel) relaxation among the Kuna volunteers:
  • Study #1 compared the vascular impact of two specially prepared cocoa drinks: one low in cocoa flavanols versus one high in cocoa flavanols;
  • Study #2 compared the vascular impact of two drinks: one containing no flavanols, versus one that contained just one cocoa flavanol, called epicatechin.
The results of the first study showed that only the group given the flavanol-rich drink enjoyed relaxation in their blood vessels.

The results of the second study showed that only the group given the drink containing isolated, cocoa-derived epicatechin

enjoyed blood vessel relaxation similar to that seen in the group that drank the flavanol-rich cocoa.

The cocoa-derived epicatechin was reported to increase the levels of nitric oxide in subjects’ blood, compared to those who drank cocoa beverages with low flavanol levels. Nitric oxide relaxes the muscles surrounding blood vessels, thereby widening them and increasing blood flow.  This observation supports earlier findings that suggested a link between cocoa’s antioxidants and increased nitric oxide production.

As study Dr. Hollenberg said, “Pinpointing specific nutrients responsible for the observed cardiovascular effects [of cocoa], as we are seeing here with epicatechin, opens up new possibilities for the development of dietary interventions for cardiovascular disease”.

It is important to emphasize that epicatechin is not the only strong antioxidant in cocoa and dark chocolate: it’s just that this study proves that at least one cocoa polyphenol—a compound abundant in tea and berries, as well—is highly effective at enhancing key aspects of cardiovascular health.

Tea and berries are good: Is dark chocolate better?
Unrefined cocoa is the uncontested champion when it comes to sheer antioxidant content, with dark chocolates offering about five times more antioxidant capacity than blueberries or green tea.  As the authors of one comparative analysis said, “These results suggest that cocoa is more beneficial to health than teas and red wine in terms of its higher antioxidant capacity.”

But it’s not clear whether the total antioxidant capacity of a food is always more important than its specific mix of antioxidants, and this may depend on the characteristics of the antioxidants in relation to someone’s individual health condition.

For example, an ounce of chocolate exceeds the antioxidant capacity of a cup of green tea considerably. But tea contains high levels of a very beneficial anti-cancer antioxidant called epigallocatechin gallate (EGCG), which is completely absent from dark chocolate. Accordingly, dark chocolate may be the better protector of heart-health, while tea is probably a more powerful anti-cancer ally.

Chocolate’s one-two antioxidant punch
Raw cocoa, and extra-dark chocolates like ours, are usually rich in both of two highly beneficial, closely related types of polyphenol antioxidants:
  • Flavan-3-ols: These include the epicatechin and catechin that make white, green, and black tea heart-healthy. Certain ones—notably the EGCG in green and white tea—possess anti-cancer properties.
  • Proanthocyanidins: Flavan-3-ols (i.e., catechin, epicatechin) can link up to form these powerfully antioxidant compounds, which are most abundant in cocoa, dark chocolate, and red wine.
How much dark chocolate is needed to enjoy its cardiac benefits? In 2002, researchers at Pennsylvania State University estimated that it takes about one ounce of antioxidant-rich chocolate to produce the immediate, short-term cardiovascular benefits seen in many studies.

They didn’t define “antioxidant-rich”, but it is likely that they had in mind typical dark chocolate, with only 60 percent cocoas solids, versus our extra-dark 80 percent cocoa bars.

If so, it would take only two-thirds of one ounce of our chocolate to produce the desire effect.  And it seems very likely that regular consumption of even smaller amounts would yield substantial beneficial effects over the long term.


Sources
  • Schroeter H, Heiss C, Balzer J, Kleinbongard P, Keen CL, Hollenberg NK, Sies H, Kwik-Uribe C, Schmitz HH, Kelm M. (-)-Epicatechin mediates beneficial effects of flavanol-rich cocoa on vascular function in humans. Proc Natl Acad Sci U S A. 2006 Jan 24;103(4):1024-9. Epub 2006 Jan 17.
  • Heiss C, Kleinbongard P, Dejam A, Perre S, Schroeter H, Sies H, Kelm M. Acute consumption of flavanol-rich cocoa and the reversal of endothelial dysfunction in smokers. J Am Coll Cardiol. 2005 Oct 4;46(7):1276-83.
  • Fisher ND, Hughes M, Gerhard-Herman M, Hollenberg NK. Flavanol-rich cocoa induces nitric-oxide-dependent vasodilation in healthy humans. J Hypertens. 2003 Dec;21(12):2281-6.
  • Holt RR, Lazarus SA, Sullards MC, Zhu QY, Schramm DD, Hammerstone JF, Fraga CG, Schmitz HH, Keen CL. Procyanidin dimer B2 [epicatechin-(4beta-8)-epicatechin] in human plasma after the consumption of a flavanol-rich cocoa. Am J Clin Nutr. 2002 Oct;76(4):798-804.
  • Sies H, Schewe T, Heiss C, Kelm M. Cocoa polyphenols and inflammatory mediators.Am J Clin Nutr. 2005 Jan;81(1 Suppl):304S-312S. Review.
  • 6:  Zhu QY, Schramm DD, Gross HB, Holt RR, Kim SH, Yamaguchi T, Kwik-Uribe CL, Keen CL.  Influence of cocoa flavanols and procyanidins on free radical-induced human erythrocyte hemolysis. Clin Dev Immunol. 2005 Mar;12(1):27-34.
  • Kris-Etherton PM, Keen CL. Evidence that the antioxidant flavonoids in tea and cocoa are beneficial for cardiovascular health. Curr Opin Lipidol. 2002 Feb;13(1):41-9. Review.
  • Wan Y, Vinson JA, Etherton TD, Proch J, Lazarus SA, Kris-Etherton PM. Effects of cocoa powder and dark chocolate on LDL oxidative susceptibility and prostaglandin concentrations in humans. Am J Clin Nutr. 2001 Nov;74(5):596-602.
  • Pearson DA, Paglieroni TG, Rein D, Wun T, Schramm DD, Wang JF, Holt RR, Gosselin R, Schmitz HH, Keen CL. The effects of flavanol-rich cocoa and aspirin on ex vivo platelet function. Thromb Res 2002;106:191-7.
  • Lee KW, Kim YJ, Lee HJ, Lee CY. Cocoa has more phenolic phytochemicals and a higher antioxidant capacity than teas and red wine. J Agric Food Chem. 2003 Dec 3;51(25):7292-5.
  • Richelle M, Tavazzi I, Offord E. Comparison of the antioxidant activity of commonly consumed polyphenolic beverages (coffee, cocoa, and tea) prepared per cup serving. J Agric Food Chem. 2001 Jul;49(7):3438-42.

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