At this point, the clinical and lab evidence that cocoa and dark chocolate benefit cardiovascular health seems pretty persuasive.
And it's very clear that these heart benefits flow from cocoa's rare blend of polyphenols, including flavanols, procyanidins, and catechins.
In fact, no cardiovascular benefits appear when people eat cocoa treated with alkali (“Dutched”) … a nearly universal cocoa-making practice that destroys most of its polyphenols.
The other top sources of cocoa-type polyphenols include grape skins, red wine, green and white tea, blackberries, boysenberries, wild blueberries, chokeberries, and Brazil's acai fruit – but cocoa is uniquely rich in all three kinds.
Better artery “performance” and lower blood pressure rank as cocoa's most convincingly demonstrated cardiovascular benefits.
As the German authors of an evidence review wrote four years ago, “The magnitude of the hypotensive [blood-pressure-lowering] effects of cocoa is … in the range that is usually achieved with … beta-blockers or angiotensin-converting enzyme [ACE] inhibitors.” (Taubert D et al. 2007)
(Despite its similar polyphenol profile, the authors found no evidence that tea reduces blood pressure.)
Last year, Australian evidence-reviewers came to a similar conclusion, and detailed the apparent upper boundaries of cocoa's powers:
“… dark chocolate is superior to placebo in reducing systolic hypertension or diastolic prehypertension. Flavanol-rich chocolate did not significantly reduce mean blood pressure below 140 mmHg systolic or 80 mmHg diastolic.” (Ried K et al. 2010)
(The U.S. National Heart, Lung, and Blood Institute defines normal blood pressure as less than 120 mmHg systolic and 80 mmHg diastolic. Stage I hypertension is defined as systolic pressure between 140 and 159 mm Hg or diastolic pressure of 90 to 99 mm Hg.)
So-called “ACE inhibitors” – drugs such as benazepril, fosinopril, and lisinopril – work by inhibiting the conversion of angiotensin I to the potent vasoconstrictor (artery tightener) angiotensin II, thereby lowering blood pressure and easing blood flow.
Swedish study affirms cocoa's healthy heart effects
The new study combined tests in human endothelial (artery-lining) cells with measurements in volunteers (Persson IA et al. 2011).
The results indicate that – like raw, non-Dutched cocoa – dark chocolate (75 percent cocoa solids) influences the genes that control blood pressure and artery dilation/relaxation.
Eating dark chocolate exerted beneficial influences over the enzyme targeted by blood pressure drugs, called angiotensin-converting enzyme or ACE.
Confirming that this effect on genes that control ACE had a practical impact, dark chocolate also lowered blood pressure in the people participating in the clinical portion of the study.
And in the test tube portion of the new study, cocoa polyphenols raised levels of nitric oxide (NO) in human endothelial cells – an effect that usually causes arteries to relax and dilate.
However, no rise in volunteers' NO levels were seen in the clinical part of the study … possibly because that effect takes longer to manifest than the three hours that passed between the time the volunteers ate chocolate and their and NO levels were tested.
Cocoa's “nutrigenomic” effects on blood pressure and arteries
Researchers at Sweden's at Linkoping University recruited 16 volunteers aged between 20 and 45 years (Persson IA et al. 2011).
Every day for two weeks, the participants ate 75 grams (2.6 ounces) of dark chocolate containing 72 percent cocoa solids.
(Any chocolate containing 60 percent or more cocoa is considered “dark”, with Vital Choice brand being 80 percent cocoa.)
The results showed a significant, 18 percent drop in ACE activity after eating the 72 percent dark chocolate … a reduction comparable to the cut produced by the leading ACE inhibitor drugs.
Interestingly, the degree of inhibition of the AC enzyme depended on the volunteers' individual “genotype” or genetic profile.
People can have one of three genotypes related to angiotensin-converting enzyme ACE, called D/D, I/D, and I/I, distributed about equally across the human population.
Three hours after consuming dark chocolate, ACE was inhibited by 21 percent in people with the I/I genotype, and by 28 percent in people with the D/D genotype.
(The authors did not report an ACE-inhibition figure for the I/D genotype, perhaps because there were too few volunteers with that type to draw a clear conclusion.)
As the Swedish team wrote, “Our results indicate that lifestyle changes, with the help of foods that contain high catechin and procyanidin content, prevent cardiovascular disease.” (Persson IA et al. 2011)
Engler MB, Engler MM, Chen CY, Malloy MJ, Browne A, Chiu EY, Kwak HK, Milbury P, Paul SM, Blumberg J, Mietus-Snyder ML. Flavonoid-rich dark chocolate improves endothelial function and increases plasma epicatechin concentrations in healthy adults. J Am Coll Nutr. 2004 Jun;23(3):197-204.
Faridi Z, Njike VY, Dutta S, Ali A, Katz DL. Acute dark chocolate and cocoa ingestion and endothelial function: a randomized controlled crossover trial. Am J Clin Nutr. 2008 Jul;88(1):58-63.
Persson IA, Persson K, Hägg S, Andersson RG. Effects of cocoa extract and dark chocolate on angiotensin-converting enzyme and nitric oxide in human endothelial cells and healthy volunteers--a nutrigenomics perspective. J Cardiovasc Pharmacol. 2011 Jan;57(1):44-50.
Ried K, Sullivan T, Fakler P, Frank OR, Stocks NP. Does chocolate reduce blood pressure? A meta-analysis. BMC Med. 2010 Jun 28;8:39.
Taubert D, Roesen R, Schömig E. Effect of cocoa and tea intake on blood pressure: a meta-analysis. Arch Intern Med. 2007 Apr 9;167(7):626-34.