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Chocolate Chalks up Big Heart-Health Win
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Johns Hopkins team reports that small amounts of dark chocolate mimic the blood-thinning benefits of aspirin
by Craig Weatherby

Lack of discipline led to unexpected scientific success in a recent study from Baltimore’s Johns Hopkins University.

Some people who volunteered for the university’s Genetic Study of Aspirin Responsiveness (GeneSTAR) didn’t obey their dietary instructions.

Key Points
  • Study confirms that dark chocolate produces anti-blood-clotting benefits like those of low-dose aspirin.
  • Dark chocolate (60% cocoa solids) was determined to be beneficial in smaller amounts than previously proved effective (about half a bar a day).
  • Extra-dark chocolate (80% cocoa solids) would yield equal benefits in even smaller amounts.
But instead of scientific failure, their disobedience led to an inadvertent and important discovery, presented November 14 at the American Heart Association's annual Scientific Sessions in Chicago.

The wayward volunteers’ inability to resist their cravings revealed that antioxidant-rich dark chocolate reduces a key cardiovascular risk factor, and that the delicious treat does it in amounts smaller than suspected possible. 

In fact, the new findings indicate that people may enhance heart health substantially by savoring just a few squares of dark chocolate a day.

The new findings are significant because previous human studies showed the same extent of anti-clotting benefit only when volunteers consumed the amounts of cocoa flavanols found in many bars of dark chocolate.

To be labeled “dark” chocolate a bar should contain 60 percent or more cocoa solids, which are the source of the flavanol antioxidants that produced significant vascular health benefits in the new study.

Extra-dark chocolates like our organic bars contain a whopping 80 percent cocoa, making them even richer in flavanol antioxidants.

How aspirin and chocolate benefit “sticky” blood
Like aspirin, the flavanol antioxidants abundant in raw, non-Dutched cocoa and dark chocolate inhibit inappropriate activation of a key component of our bodies’ clotting mechanism: the cell-like but nucleus-free bodies called blood platelets.

Let's quickly review the role that platelets play in increasing the “stickiness” of heart patients’ blood and raising their risks of suffering heart attacks or strokes.

When the endothelial tissue that constitutes the lining of blood vessels is damaged, the structural protein underneath it (collagen) comes into contact with blood.

Any such collagen-exposing breach in the endothelial lining induces the body to release chemicals that cause blood platelets to stick to each other in a process called “activation”. In turn, activated platelets release chemicals that activate surrounding platelets, eventually producing a clot.

While platelet activation usually occurs in response to cuts or other wounds, it can also happen when oxidized cholesterol and fatty acids in the blood begin to form plaques on artery walls: a condition called atherosclerosis.

Oxidized cholesterol and fatty acids infiltrate the endothelial lining and promote chronic platelet activation. In turn, sustained platelet activation promotes formation of artery-narrowing plaques, which are unstable and can breach, releasing chunks of fatty material that can block an artery.

Constant platelet activation becomes especially dangerous in blood vessels narrowed by atherosclerosis, since it can easily cause flow-blocking clots.

Aspirin and cocoa share anti-inflammatory actions
Formation of the arterial plaques that define atherosclerosis is an incompletely understood process, but inflammation is both a cause and effect of plaque accumulation, thanks in part to its ability to promote platelet activation.

The vicious inflammatory cycle that occurs in heart patient’s blood vessels explains why researchers wondered whether aspirin
which exerts strong anti-inflammatory effectsmight reduce unwanted platelet activation and its killer consequences.

Scientists' aspirin-research endeavors proved very successful, and daily low-dose aspirin has saved many lives by reducing platelet activation and the consequent risks of atherosclerosis, heart attacks, and strokes.

But aspirin isn’t the only anti-inflammatory agent available to us. Certain foods contain antioxidants with potent anti-inflammatory effects.

Chief among these beneficial plant compounds are the flavanol-type polyphenols abundant in tea, berries, and chocolate: especially the catechin-class flavanols in which raw, non-Dutched cocoa and extra-dark chocolate are extremely rich.

Like aspirin (acetylsalicylic acid)which is an altered version of the salicylic acid found in many plant foodsthe catechin antioxidants in cocoa inhibit inflammation by blocking expression of enzymes called cyclooxygenase 1 and cyclooxygenase 2 (COX-1 and COX-2).

However, aspirin appears to block the COX-1 enzyme unconditionally, with adverse side effects that include gastric bleeding. Likewise, the largely discredited drugs Celebrex and Vioxxwhich were touted as safer than aspirin for long-term, high-dose useblock the COX-2 enzyme unconditionally, with adverse side effects that include increased risk of heart attacks.

In contrast, the catechin antioxidants in cocoa (and the antioxidant polyphenol pigment curcumin, found in turmeric) only block the COX-2 enzyme conditionally--that is, when inflammation is out of control--and therefore produce no adverse side effects.

Study affirms dark chocolate as comparable to aspirin
The new findings about dark chocolate flowed, inadvertently, from a study intended to discover how genes might influence the way aspirin discourages unnecessary activation of blood platelets (Becker D et al 2006).

That investigation, called GeneSTAR (Genetic Study of Aspirin Responsiveness) was led by Diane Becker, M.P.H., Sc.D. of Johns Hopkins University. The GeneSTAR study was designed to discover whether gene-driven variations in blood clotting affect patients’ responses to low-dose aspirin therapy.

Dr. Becker’s team enrolled 1,200 volunteers, all of whom had a slightly elevated risk of heart disease, due in part to excessive platelet activation.

The study ran from June 2004 to November 2005 and involved more than 500 men and 700 women from all around the US. Participants ranged in age from 21 to 80; 31 percent were African-American and the rest were of primarily European heritage.

At the outset, the volunteers agreed to exercise and refrain from smoking or consuming foods and drinks that affect platelet activation substantially, including coffee, tea, caffeinated sodas, berries, wine, grapefruit juice, and chocolate.

Among the volunteers, 139 admitted consuming chocolate, cocoa, grapes, black or green tea and strawberries. But while they were excluded from the aspirin study, Dr. Becker and her team decided to test their blood for chocolate's effect on blood platelets.

Researchers have known for nearly two decades that dark chocolate lowers blood pressure and exerts beneficial effects on three factors that affect blood flow: arterial stiffness, platelet reactivity and activation, and endothelial (artery lining) function.

The Johns Hopkins group conducted more than 200 different tests of platelet reactivity on the participants’ blood, with results that showed its effects are comparable to those of low-dose aspirin therapy.

For example, platelet samples from those who stuck to the no-chocolate regimen and the “violators” who kept eating chocolate were run through a machine that determines the duration of delay in platelet aggregation (clumping) in capillary-like tubes.

The results showed that blood platelets from the chocolate-consumers took longer to clot, compared with blood platelets from the more obedient volunteers, who avoided chocolate (130 seconds versus 123 seconds).

And a urine test for byproducts of platelet activation (e.g., thromboxane and creatinine) proved that there’d been substantially less platelet activation among the chocolate eaters.

Dark chocolate proven beneficial to platelets in small amounts
The big surprise for the Baltimore team was that clot-preventing platelet de-activation effects occurred among people who’d consumed only modest amounts of dark chocolate.

Prior human studies that demonstrated chocolate’s vascular benefits recorded decreased platelet activity in response to doses of flavanols equivalent to the amounts found in several bars to many bars of dark chocolate.

But the Baltimore study found that the disobedient volunteers showed substantial anti-clotting benefits after eating amounts of dark chocolate as small as two tablespoons (a few squares) per day.

As Dr. Becker told the Johns Hopkins news service, “What these chocolate ‘offenders’ taught us is that the chemical in cocoa beans has a biochemical effect similar to aspirin in reducing platelet clumping...”

She went on to say, “People who ate chocolate had markedly lower amounts of... this byproduct of platelet activity, which meant that the platelets are not being activated and not clumping so much in the body. The magnitude of the difference is very significant.”

Becker noted that standard milk-chocolate candy contains heart-unhealthful amounts of sugar and saturated milk fats. The 63-year-old scientist told the Baltimore Sun that instead of milk chocolate, she enjoys half a bar of dark, low-fat, low-sugar chocolate every day. “The reason I do it is because I'm so proscriptive about everything else in my diet ... I look forward to that all day.”

That’s one prescription most of us can accept with pleasure!

  • Becker D, Faraday N, Yanek L, Moy T, Becker L. Casual chocolate consumption and platelet activity. American Heart Association Scientific Sessions 2006, Chicago. Oral presentation #11865, Room S106b, Nov. 14 2006.
  • Aznaouridis K et al. Dark Chocolate Improves Endothelial Function And Arterial Stiffness In Healthy Individuals. American Heart Association Scientific Sessions 2004. Session Number/Title: AOP.41.1 Nutrition and Cardiovascular Diseases
  • Presentation Number: 3584
  • Engler MB, Engler MM. The emerging role of flavonoid-rich cocoa and chocolate in cardiovascular health and disease. Nutr Rev. 2006 Mar;64(3):109-18. Review.
  • Innes AJ, Kennedy G, McLaren M, Bancroft AJ, Belch JJ. Dark chocolate inhibits platelet aggregation in healthy volunteers. Platelets. 2003 Aug;14(5):325-7.
  • Murphy KJ, Chronopoulos AK, Singh I, Francis MA, Moriarty H, Pike MJ, Turner AH, Mann NJ, Sinclair AJ. Dietary flavanols and procyanidin oligomers from cocoa (Theobroma cacao) inhibit platelet function. Am J Clin Nutr. 2003 Jun;77(6):1466-73.
  • 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 May 15;106(4-5):191-7.

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