February 13, 2009
By Harvey B. Simon, M.D.
Harvard Medical School
It's Valentine's Day. Perhaps you're lucky enough to have someone you care about and who cares about you. Often, the gift you send or receive will be chocolate. It may be a gift from the heart, but what will it do to your heart? Is chocolate a forbidden treat or might it actually be a boon to health?
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The Heart of Chocolate
Chocolate doesn't grow on trees, but cacao beans do. After harvesting, the beans are dried for several days and then roasted. Next, the beans are opened; the shells are discarded, and the nibs are ground and separated into cocoa butter and cocoa powder. The powder is low in fat and is used for baking or to make hot chocolate. The cocoa butter is the heart of chocolate.
Cocoa butter is dark and rich, but it tends to be bitter. To make chocolate sweeter, manufacturers add sugar, which also adds calories. And to make milk chocolate, candy makers really do add milk solids, which include saturated fats. Bottom line: Processing may make chocolate look lighter and taste sweeter, but it also removes healthy ingredients and adds harmful ones.
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A Bite of Chemistry
The cocoa bean is devilishly complex. It contains more than 400 chemicals and substances. Many of them can affect human biology and health.
- Fats Cocoa butter is high in fat. It's what gives chocolate its tempting texture and "mouth feel." But it's also what gives chocolate its bad name. Although it's true that the fat has lots of calories, it's not guilty of the charge that it boosts blood cholesterol levels.
- Flavanols The humble cacao bean contains a number of chemicals in the flavanol family. This is a group of chemicals that are responsible for many of the protective actions of chocolate. Flavanols are found in many healthful foods including apples and red wine. But dark chocolate is the richest source.
- Amino acids Chocolate is high in chemicals that help make the "stress hormone," adrenaline, and dopamine, a chemical that relays signals between nerve cells in the brain. Scientists think that dopamine triggers feelings of pleasure. If so, the passionate craving of the true chocoholic may have a chemical basis. But these same chemicals may also explain some of the side effects of chocolate.
- Caffeine Chocolate contains caffeine and a similar chemical that may explain why chocolate makes some hearts beat faster. These chemicals relax the muscle between the stomach and the esophagus, which allows acid to back up from the stomach into the sensitive "food pipe." That's why chocolate gives many people heartburn.
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Scientists from around the world have studied chocolate's effect on people's health. For example:
- Antioxidant activity Scientists from Italy and Scotland fed dark chocolate, milk chocolate, or dark chocolate and a glass of whole milk to healthy volunteers. Dark chocolate boosted the volunteers' blood antioxidant activity. But milk, either in the chocolate or a glass, prevented the effect.
- Vascular function The inner layer of arteries makes a tiny chemical that widens blood vessels and keeps their linings smooth. Doctors in Greece think chocolate may help keep vessels open. They fed 100 grams (about 3½ ounces) of dark chocolate to 17 healthy volunteers. Their vascular function improved rapidly. Swiss investigators found similar effects from dark chocolate but no benefit from white chocolate.
- Blood pressure Because good vascular function widens blood vessels, it's logical that chocolate might help lower blood pressure. Studies from Italy, Argentina, Germany and the United States have shown that dark chocolate can lower blood pressure in healthy adults and in patients with hypertension. But the benefit is modest and it wears off within a few days of stopping "treatment" with a daily "dose" of dark chocolate.
- Insulin sensitivity People with diabetes have good reason to avoid chocolate. It's got lots of sugar and calories. But an Italian study suggested that dark, not white, chocolate can improve insulin sensitivity. However, a 2008 investigation of flavanol-enriched cocoa found no improvement in blood sugar or blood pressure.
- Blood clotting Most heart attacks and many strokes are caused by fatty deposits called plaques that contain cholesterol. The build-up of plaque can cause a blood clot to form. Researchers in Switzerland and the United States found that dark chocolate reduces blood cell activity that can lead to clot formation.
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From the Lab to Life
Given this evidence, chocolate could reduce the risk of heart attack and stroke. But all of these hopeful results are based on short-term experiments in a small number of volunteers. Do these bits and pieces of data apply to real life?
Perhaps. The strongest support for chocolate as a health food comes from a 2006 report from the widely respected Zutphen Elderly Study. Researchers evaluated 470 Dutch men between the ages of 65 and 84. All subjects were free of diabetes, cardiovascular disease, and cancer when the study began in 1985. Each volunteer provided comprehensive dietary information, and had his blood pressure, cholesterol, body fat, and other cardiovascular risk factors evaluated.
Researchers tracked the men for 15 years. They found that the men who ate the most cocoa-containing products had lower blood pressures than those who ate the least. The average difference was 3.7 mm Hg in systolic pressure and 2.1 mm Hg in diastolic. These differences may not seen substantial, but even after taking other risk factors into account, the chocolate lovers also enjoyed a 47% lower death rate. Most of the benefit was due to a sharply decreased risk of heart disease. And the largest single source of cocoa was dark chocolate.
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Raising the Bar
To the ancient Mayans, chocolate was the food of the gods. Many modern Americans agree. But others fear "death by chocolate." They assume that anything tasting so good must be bad for you. Is chocolate a divine food or a devilish temptation?
New research suggests that chocolate may indeed have a role in promoting vascular health. But the devil is in the details. Dark chocolate appears beneficial, but milk chocolate, white chocolate and other varieties are not. Most trials have used 100 grams of dark chocolate, about one and a half chocolate bars of typical size. If you ate that much every day, you'd pack in more than 500 extra calories and gain a pound a week. And if that's not bad enough, remember that chocolate can trigger migraines, heartburn or kidney stones in susceptible people.
If you're a chocolate lover, dark chocolate can be part of a healthy lifestyle. To have the pleasure without the guilt:
- Choose dark chocolate.
- Make sure the first listed ingredient is cocoa or chocolate liquor, not sugar.
- Limit yourself to a few ounces a day, and cut calories elsewhere to keep your weight in line.
- Don't rely on chocolate to make up for a bad diet or insufficient exercise.
In the past few years, modern science has learned a lot about this ancient food. Even so, more chocolate research is needed. Any volunteers?
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Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.