Chocolate is good for you -- and other sweet myths

For dark-chocolate lovers, the medical study findings couldn't have been more delicious: Their guilty pleasure can ward off heart disease.

But if it sounds too sweet to be true, it is. The logic doesn't just melt in your mouth; it melts under the skeptical eye of Robert Davis, author of "The Healthy Skeptic."

"The truth is that there have been small, short-term studies suggesting dark chocolate in large quantities may have some short-term, positive effects on the cardiovascular system, but it's unclear whether there are any long-term benefits, and that's what counts," says Davis, a health journalist who teaches at Emory University's Rollins School of Public Health in Atlanta. "It gets translated to say dark chocolate is good for you, and that is a huge exaggeration of the truth."

Based on other studies, blueberries, almonds and even onions also have catapulted to celebrity status, thanks to marketing, media and eager consumers, Davis says.

"No food by itself has that kind of power," he says.

Here is his advice on other popular medical claims:

Healthy Skeptic: There is much more to heart health than cholesterol. Only half of people who have had heart attacks had high cholesterol levels.

Healthy Skeptic: Vitamins help convert carbohydrates into energy, but they are not a source of energy. Only food supplies energy.

Bottom line: You do not need extra doses of Vitamin B. You can get what you need from your diet and daily multivitamin.

Healthy Skeptic: Blueberries have antioxidants. But there's no basis to suggest that blueberries are better for you than strawberries or watermelon or that they will prevent Alzheimer's.

Bottom line: Stop fixating on any one fruit, and focus on eating a variety of fruits and vegetables.

Healthy Skeptic: There is evidence that a glass of wine every night might be good for your heart, but the risk of drinking too much is far greater than drinking just the right amount.

Healthy Skeptic: Sunscreen prevents sunburn and can prevent squamous skin cancer, but there is not strong evidence that it prevents melanoma.

Bottom line: Avoiding sun, staying in the shade and wearing wide-brimmed hats are more effective. Sunscreen should not be a first defense.

Healthy Skeptic: The production of Teflon involves a chemical called perfluorooctanoic acid (PFOA). Studies in rodents show that it might cause cancer and birth defects. Virtually all Americans have PFOA in their blood, but the levels tend to be extremely low -- about 5 parts per billion. That's up to 25,000 times less than the amount demonstrated to cause harm in lab animals.