Chocolate is made from cocoa, which contains polyphenols, which may work as antioxidants that lower LDL cholesterol (the bad kind) and reduce blood pressure. Some experts suggest that eating some chocolate every day can decrease your risk of cardiovascular diseases.
Cocoa contains epicatechins and catechins, which are similar to the polyphenols found in green tea; and quercetin, which is found in fruits and vegetables. Dark chocolate has more antioxidants than milk chocolate because certain processing methods remove the polyphenols, which have a bitter flavor.
Research studies as far back as 2006 looked at chocolate consumption and how it correlated with cardiovascular disease risk in large populations, and found a correlation. People who consumed more chocolate of any kind tended to have a lower risk of cardiovascular disease. This is interesting information, but the problem with these types of nutrition studies is the large possibility of confounding factors. If people who eat chocolate also do other things that decrease their risk of cardiovascular diseases, researchers and reporters can come to the wrong conclusion.
It's better to have randomized control trials, which are studies in which one specific therapy (in this case chocolate or cocoa) is studied in such a way that confounding factors are eliminated or at least minimized.
Cocoa appears to have beneficial effects on the function of blood vessels, so it's possible that chocolate could help people with high blood pressure. Several studies on chocolate's effect on blood pressure have been completed, and many (but not all) of them demonstrate a decrease of blood pressure readings for the subjects who had high blood pressure.
Unfortunately, there are a couple of problems. The studies that showed decreases in blood pressure were mostly open-label studies. That means both the subjects and researchers knew what they were taking and why they were taking it. That's a big issue because when people know that the substance they're taking may improve their health, they're more likely to show health improvements that have nothing to do with that substance (it's called the placebo-effect). Most of the studies that were double-blind studies (neither the researcher nor the subjects knew if they were taking the real chocolate or a placebo) didn't show that same decrease in blood pressure.
Another problem with these studies is that different brands of chocolate were used in different studies. Processing methods may vary greatly from company to company (and often those methods are secret) so the quality and amounts of antioxidants could have differed.
Polyphenols like those found in chocolate may be able to lower cholesterol. Research findings from two different studies published in 2010 showed some promise that cocoa could reduce LDL cholesterol and increase HDL cholesterol (the good kind). But they were small studies. Larger studies are needed to see how much affect cocoa really has on cholesterol levels.
Cocoa also contains small amounts of xanthines (theobromine, theophylline and caffeine) and another compound called phenylethylamine. But since chocolate contains only small amounts of these compounds they probably don't have any impact on your health.
It's possible that eating a small amount of chocolate (dark chocolate has the most antioxidants) may help reduce your blood pressure (if you have high blood pressure), but the evidence isn't all that strong. So when you balance that with the added fat and sugar found in chocolate treats, you need to watch the amount you consume. A small amount of dark chocolate (less than 100 to 200 calories based upon your daily need) is fine, but don't think of it as medicine and expect it to lower your blood pressure; there may be many other lifestyle and dietary factors involved.
Almoosawi S, Fyfe L, Ho C, Al-Dujaili E. "The effect of polyphenol-rich dark chocolate on fasting capillary whole blood glucose, total cholesterol, blood pressure and glucocorticoids in healthy overweight and obese subjects.". Br
Buitrago-Lopez A, Sanderson J, Johnson L, Warnakula S, Wood A, Di Angelantonio E, Franco OH. 'Chocolate consumption and cardiometabolic disorders: systematic review and meta-analysis." J Nutr. 2010 Mar;103(6):842-50. BMJ. 2011 Aug 26;343:d4488. doi: 10.1136/bmj.d4488.
Egan BM, Laken MA, Donovan JL, Woolson RF. "Does dark chocolate have a role in the prevention and management of hypertension?: commentary on the evidence." Hypertension. 2010 Jun;55(6):1289-95.
Erdman JW Jr, Carson L, Kwik-Uribe C, Evans EM, Allen RR. "Effects of cocoa flavanols on risk factors for cardiovascular disease." Asia Pac J Clin Nutr. 2008;17 Suppl 1:284-7.
Lamuela-Raventós RM, Andrés-Lacueva C, Permanyer J, Izquierdo-Pulido M. "More antioxidants in cocoa." J Nutr. 2001 Mar;131(3):834-5.
Mellor DD, Sathyapalan T, Kilpatrick ES, Beckett S, Atkin SL. "High-cocoa polyphenol-rich chocolate improves HDL cholesterol in Type 2 diabetes patients." Diabet Med. 2010 Nov;27(11):1318-21.
Njike VY, Faridi Z, Shuval K, Dutta S, Kay CD, West SG, Kris-Etherton PM, Katz DL. "Effects of sugar-sweetened and sugar-free cocoa on endothelial function in overweight adults." Int J Cardiol. 2011 May 19;149(1):83-8.