|In this issue of HEALTHbeat:
• Chocolate and your health — guilty pleasure or terrific treat?
• What should an exam for skin cancer include?
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|March 3, 2009|
Dear HEALTHbeat subscriber,
Like coffee and alcohol, chocolate has long been considered a guilty pleasure that’s probably best avoided. But, like those other former dietary “bad boys,” chocolate has been partially redeemed in recent years by news of its health benefits — at least when consumed in moderation. This issue of HEALTHbeat explains what chocolate can do for your health, and what type is most beneficial. Also in this issue, Dr. Kenneth Arndt, editorial board member of the Harvard Health Letter, discusses what steps an exam for skin cancer should include.
Wishing you good health,
|Chocolate and your health — guilty pleasure or terrific treat?|
The cacao bean, from which chocolate is made, is devilishly complex, containing more than 400 chemicals. Many of them can affect human biology and health. Whether chocolate is good or bad for you depends largely on the type of chocolate and the amount you consume.
Fats. About a third of the fat in cocoa butter is oleic acid, the very same monounsaturated fat that gives olive oil its good name. Another third is stearic acid; it is a saturated fat, but unlike the three other saturated fats in the human diet, stearic acid does not raise cholesterol levels because the body can metabolize it to oleic acid. And while chocolate also contains some palmitic acid, a saturated fat that does boost cholesterol, careful studies show that eating chocolate does not raise blood cholesterol levels.
Flavonoids. The humble cacao bean contains a number of chemicals in the flavonoid family. Polyphenols protect chocolate from turning rancid, even without refrigeration. Even more important are the flavanols, a group of chemicals that are responsible for many of the protective actions of chocolate. Flavanols are present in many healthful foods—like apples, cherries, and black tea—but dark chocolate is the richest source.
Amino acids. Chocolate is high in tryptophan, phenylalanine, and tyrosine. Like other amino acids, these nitrogen-rich compounds are the building blocks of all the body’s proteins. But two of these amino acids have a unique property: they are precursors of adrenaline, a “stress hormone,” and dopamine, a neurotransmitter that relays signals between nerve cells in the brain. Scientists postulate that dopamine induces feelings of pleasure. But these chemicals may also explain some of the adverse effects of chocolate, including its ability to trigger headaches in some migraine sufferers, its ability to raise blood pressure to dangerous levels in some patients taking monoamine oxidase inhibitors for depression, and its ability to instigate diarrhea, wheezing, and flushing in patients with carcinoid tumors, which are rare.
Methylxanthine. Chocolate contains two members of this group of chemicals. One is obscure, the other notorious — but both theobromine and caffeine have similar effects on the body. They may explain why chocolate makes some hearts beat faster — and why it gives many people heartburn by relaxing the muscle between the stomach and the esophagus, thus allowing acid to reflux up from the stomach into the sensitive “food pipe.”
The flavonoids have many properties that might improve health. To see if they really work, researchers have studied foods ranging from apples to onions, and from tea to wine. And it’s no surprise that chocolate has attracted the interest of scientists from around the world, giving the research an international flavor. Most studies concentrate on aspects of cardiovascular health; here are some representative findings:
Antioxidant activity. Antioxidants protect many of the body’s tissues from damage by oxygen free radicals. Among other beneficial actions, flavonoids protect LDL cholesterol from oxidation, which puts the “bad” into “bad cholesterol.” Here are two examples. Scientists from Italy and Scotland fed dark chocolate, milk chocolate, or dark chocolate and 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. Similarly, researchers in Finland and Japan found that dark chocolate reduces LDL oxidation while actually increasing levels of HDL (“good”) cholesterol, but white chocolate lacks both benefits.
Endothelial function. The endothelium is the thin inner layer of arteries. It’s responsible for producing nitric oxide, a tiny chemical that widens blood vessels and keeps their linings smooth. Can chocolate help? Doctors in Greece think it may. They fed 100 grams (about 3½ oz) of dark chocolate to 17 healthy volunteers and observed rapid improvement in endothelial function. Swiss investigators found similar effects from dark chocolate. German scientists reported that flavanol-rich cocoa can reverse the endothelial dysfunction produced by smoking, and European doctors reported that dark chocolate appears to improve coronary artery function in heart transplant patients. There’s good news for nonsmoking, original-heart people, too, since Harvard researchers found that cocoa can blunt the endothelial dysfunction associated with aging.
Blood pressure. Because good endothelial function widens blood vessels, it’s logical that chocolate might help lower blood pressure. Studies show that dark chocolate can lower blood pressure in healthy adults and in patients with hypertension. Research shows that the effect is modest, however, lowering systolic pressure (the higher number recorded, when the heart is pumping blood) and diastolic blood pressure (the lower number, recorded while the heart is resting between beats) by just under 5 millimeters of mercury (mm Hg). The benefit wears off within a few days of stopping “treatment” with a daily “dose” of dark chocolate. And another reality check comes from a six-week 2008 study of 101 healthy adults that did not find any benefit for blood pressure.
Insulin sensitivity. The sugar and calories in chocolate give people with diabetes good reason to eschew it. But an Italian study in nondiabetics suggested that dark, but not white, chocolate can improve insulin sensitivity. However, a small 2008 investigation of flavanol-enriched cocoa in diabetics found no improvement in blood sugar control or blood pressure.
Blood clotting. Most heart attacks and many strokes are caused by blood clots that form on cholesterol-laden plaques in critical arteries. These clots are triggered by platelets; the antiplatelet activity of aspirin explains its important role in patients with coronary artery disease. Researchers in Switzerland and the U.S. found that dark chocolate reduces platelet activation.
From lab to life
International experiments show that dark chocolate has an impressive array of activities: it is an antioxidant that may improve your cholesterol; it improves endothelial function and may lower your blood pressure; it is a sweet that may lower your blood sugar; and its antiplatelet activities could reduce your chances of developing an artery-blocking clot. Taken together, these properties 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.
Research suggests that chocolate may indeed have a role in promoting vascular health, but the devil is in the details. The first consideration is the type of chocolate. Dark chocolate appears beneficial, but milk chocolate, white chocolate, and other varieties do not. The second issue is calories. Most trials have used 100 grams of dark chocolate, the equivalent of eating 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, enough to gain a pound a week.
If you’re a chocolate lover, choose dark chocolate; the first listed ingredient should be cocoa or chocolate liquor, not sugar. Limit yourself to a few ounces a day, and cut calories elsewhere to keep your weight in line.
For more information about how food affects your health, order our Special Health Report, Healthy Eating: A guide to the new nutrition, at www.health.harvard.edu/HE.
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|What should an exam for skin cancer include?|
Q: Since having a basal cell carcinoma removed from my forehead in 1992, I’ve gotten a full-body examination by a dermatologist every six months. In addition to the basal cell carcinoma, I’ve had several melanocytic nevi removed from my back, neck, and hairline.
I recently went to a new dermatologist. My previous exams had taken about half an hour. The doctor checked my entire body under bright lights, including looks between my toes and a careful inspection of my scalp, and a nurse noted mole measurements in my medical chart. My new dermatologist just took a quick look at my back, arms, and legs — he said there’s no need to examine areas that wouldn’t have been sunburned in the past — and no bright lights were used. I wonder what the standard is for a full-body exam.
A. There are three main types of skin cancer: basal cell, squamous cell, and melanoma. Basal cell is the least serious of these because it’s the least likely to spread, or metastasize. There’s no question that exposure to sunlight, particularly the ultraviolet (UV) portion of the light spectrum, is a risk factor for basal and squamous cell skin cancers. Both types occur on the head, the face, and other areas of the body that get lots of sun exposure.
People like you who have had basal cell skin cancer are supposed to come in regularly for skin cancer checks. The National Cancer Institute guidelines say basal cell patients should be examined every six months for five years and annually thereafter. The American Cancer Society’s recommendations are similar. These aren’t just exams for basal cell skin cancer. Doctors should be looking for signs of squamous cell skin cancer and melanoma, too, because, as I mentioned, the risk factors for the different kinds of skin cancer likely overlap and the same sorts of people are vulnerable. That means the doctor should examine not just the sun-exposed areas, but the entire body, including the back, the scalp, and between the toes, because melanoma can first appear in areas not exposed to the sun. The skin near the genitals and anus should also be inspected. In my office, we always ask patients who are getting a skin cancer exam to get into a hospital gown so the exam can be thorough.
So I think your current dermatologist is doing a cursory job. But from what you’ve said, it also seems like the previous one was going a bit overboard.
Half an hour is an awfully long time for a routine skin cancer exam; typically, my exams take 10 to 15 minutes. Good lighting is essential, but a doctor doesn’t need any special equipment. And you may be coming in for exams too often. You had basal cell cancer more than 15 years ago. The guidelines I’ve mentioned recommend annual, not semiannual, exams.
In fact, as a practical matter, I and many other dermatologists examine basal cell cancer patients annually even within the first five years after their initial treatment. The exams are important — about 40% of people who have basal cell carcinoma will get a second lesion, although not in the same place, within three years after the first one is treated. But in my experience, it’s hard enough to get busy people to come back for a check on a yearly basis.
You mention that you’ve had some melanocytic nevi removed. Melanocytic nevi is the medical term for moles, and by definition, moles are benign. Moles and their removal aren’t a reason for having more frequent skin exams.
I’d talk to your current dermatologist about doing a more thorough exam for all sorts of skin cancer. But I’d also recommend getting that exam once — not twice — a year.— Kenneth A. Arndt, M.D.
SkinCare Physicians, Chestnut Hill, MA
Harvard Health Letter Editorial Board
This Question and Answer first appeared in the January 2009 Harvard Health Letter, available at www.health.harvard.edu/health.
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