Take people who are free of cardiovascular disease and ask them what they eat. Then, years later, find out if they’ve had a heart attack or stroke or have high blood pressure.
“Generally, those who report consuming the most chocolate at the start of the study are less likely to later be diagnosed with cardiovascular disease,” says Kevin Monahan, a physiologist and associate professor of medicine at the Penn State College of Medicine in Hershey.
In two Swedish studies, for example, people who ate the most chocolate had a lower risk of stroke or a fatal heart attack than those who ate the least. (The “most” was about two ounces a week in one study and at least twice a week in the other.)
“That makes chocolate sound great,” says Monahan. “But those studies are limited because they’re observational. You don’t know if the result is an effect of eating chocolate, or if it has something to do with other factors that differ in people who eat chocolate.”
It could be that someone who eats chocolate every week is demonstrating restraint and willpower, says Catherine Kwik-Uribe, director of research and development for Mars Symbioscience, a scientific division of the candy giant that makes Snickers, M&M’s, and other chocolates.
“So what we may actually be seeing is evidence of a disciplined approach to health and lifestyle that’s reflected in the food choices they make, as opposed to the chocolate itself being the cause of their good health.”
That’s why scientists have conducted dozens of randomized controlled trials during the past decade in which they compared (flavanol-rich) dark chocolate to (flavanol-free) white chocolate, or they compared flavanol-enriched cocoa to low-flavanol cocoa. If flavanols—rather than something else about people who consume flavanols—matter, those studies should pick it up.
Blood flow. “Large amounts of cocoa flavanols have consistently improved endothelial function in studies in healthy young people, in patients with coronary artery disease, and in people with diabetes or high blood pressure,” says Monahan.
Endothelial function is a measure of how an artery responds to an increase in blood flow. (The endothelium is the inside lining of blood vessels.)
“The endothelium is a barometer of the health of your blood vessels,” says Joseph Vita, a professor of medicine and senior staff cardiologist at the Boston University School of Medicine.
“That’s because it’s one of the first things to go wrong on the path to atherosclerosis, which is the underlying cause of heart attack and the most common form of stroke. If your arteries are stiff, that means your heart has to work harder to pump the blood out.”
Flavanols seem to increase the body’s ability to synthesize nitric oxide, which triggers the dilation of arteries.
“Relaxing, or dilating, is good because it’s the way to get more blood, and more oxygen, flowing,” notes Monahan. “It’s like adding an extra lane to a highway so that more cars can get through.”
In a study funded by chocolate maker Hershey, Monahan and his colleagues found that blood flow in the arteries increased within two hours after older people consumed cocoa flavanols in a beverage, compared with another time when they got a placebo drink.
But Hershey’s milk chocolate division may not have been jumping for joy. Blood flow improved in people given high doses of flavanols (180, 465, or 1,095 milligrams), but not in those who got 70 mg. The classic 1½ oz. Hershey’s Milk Chocolate bar contains about 25 mg of flavanols.
Last year, the European Food Safety Authority approved a health claim for cocoa and chocolate and endothelial function after concluding that 200 mg or more of flavanols could “help maintain endothelium-dependent vasodilation, which contributes to normal blood flow.” (The EFSA is the equivalent of the U.S. Food and Drug Administration.)
Blood pressure. Improved endothelial function could explain why cocoa or chocolate that contained large amounts of flavanols produced “a small but statistically significant effect in lowering blood pressure by 2-3 mm Hg in the short term.”
That’s what the Cochrane Collaboration, an international network of scientists who evaluate the research for medical therapies, concluded in 2012 after reviewing 15 randomized controlled trials that lasted from 2 to 18 weeks.
But the trials tested an average of 560 milligrams of flavanols a day. You’d have to eat 5½ ounces of dark chocolate to get that much.
The European Food Safety Authority hasn’t been impressed with the research. The evidence is “insufficient” for chocolate manufacturers to claim that cocoa and chocolate can lower blood pressure, it declared.
Sources: Neurology 79: 1223, 2012; J. Intern. Med. 266: 248, 2009; Arch. Biochem. Biophys. 527: 90, 2012; J. Appl. Physiol. 111: 1568, 2011; Cochrane Database Syst. Rev. 8: CD008893, 2012.
Other relevant links:
- Can you eat milk chocolate to improve your circulation? See: What to Eat: Are Cocoa and Chocolate a Reliable Source of Flavanols?
- Do the flavanols in chocolate help prevent cognitive decline? See: Chocolate and Brain Health
- Heart health requires more than just limiting saturated fat intake. See: What Can People Do to Protect Their Heart?