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Cinnamon, the unofficial aroma of the holidays, is a surprisingly complex spice.

It's not just the flavor, both sweet and fiery, that's full of contradictions. Nutritionally, it could be described as both unremarkable and packed with potentially healthy compounds. It comes with an irresistible warm flavor – and also some warnings.

Before cinnamon could be found on everybody's spice rack, people searched the world for it. It helped inspire the voyages of Christopher Columbus and Vasco da Gama and wars and conquests around the globe.

Even the label on the jar carries more meaning than you'd think, because the spice, which is harvested from the bark of a bushy evergreen tree in the laurel family, comes in many varieties.

Ceylon cinnamon, or "true" cinnamon, goes by the scientific name of Cinnamomum verum and is grown mostly in Sri Lanka. In the United States, the most commonly sold type is cassia cinnamon or, formally, Cinnamomum cassia. The cassia variety is sometimes called Chinese cinnamon, although variants are grown elsewhere in Southeast Asia. Most of the U.S. supply comes from Indonesia.

Cassia cinnamon has a stronger flavor and different chemical profile than the Ceylon variety, and one of the challenges in understanding cinnamon is that studies don't always distinguish the variety, said Dr. Connie Rogers, a professor and head of the department of nutritional sciences at the University of Georgia in Athens.

"There's been a lot of work in clinical trials and in preclinical models, and sometimes the forms haven't been identified clearly," she said. "So I think that one of the questions is, 'Is all cinnamon created equal in terms of health benefits?' And I don't think we really know the answer to that yet."

In any form, cinnamon adds little in terms of basic nutrients. According to the U.S. Department of Agriculture, 1 teaspoon provides traces of vitamins and minerals, plus about 6 calories.

That makes cinnamon a "safe and easy way" to flavor food without adding significant calories to the dish, Rogers said.

Cinnamon also is full of plant-based chemicals called polyphenols that might offer health benefits. One of them, cinnamaldehyde, gives cinnamon its aroma and flavor.

Such bioactive ingredients, Rogers said, work as antioxidants to prevent tissue damage and limit inflammation. Chronic inflammation is a risk factor for cardiovascular disease and other health problems. And "cinnamon may be a really great dietary addition to help prevent or control that inflammation," she said.

Some studies have shown that cinnamon may help to lower blood glucose for people with Type 2 diabetes. A study in the American Journal of Clinical Nutrition found that people who ingested Indonesian cinnamon (Cinnamomum burmannii) for two weeks had lower glucose levels than people who took a placebo.

Similarly, cinnamon also has been studied for its effects on blood cholesterol levels, but findings have been mixed in that area.

Unlike spices that have been studied mostly in concentrated form, cinnamon studies have used relatively small amounts that an average person might consume in a day, Rogers said, so people should "absolutely" check with their doctor before increasing how much they eat regularly, especially if they are taking it as a dietary supplement.

"It's certainly not recommended to replace diet, exercise and any pharmacological treatment that somebody's taking for a clinical condition like diabetes," she said.

And while the research on blood glucose is promising, she said, overall the research on cinnamon is "too new" to draw any solid conclusions about possible medicinal properties. "There appear to be health benefits in some of the clinical research, and in some other research, there doesn't seem to be a benefit." Cinnamon appears to be safe, she said, but "clearly we don't completely understand how this is working."

Some aspects of cinnamon require special attention.

Compared with Ceylon cinnamon, cassia cinnamon contains high levels of coumarin, which can harm the liver. The National Center for Complementary and Integrative Health says that in most cases, consuming cassia cinnamon would not cause significant problems, but prolonged use could be an issue for people living with liver disease.

And since last year, the Food and Drug Administration has issued several recalls for various brands of cinnamon because of high levels of lead. A list of products is posted on the .

Overall, Rogers said, cinnamon can add flavor without adding calories, salt or sugar. Some of her own research has involved using cinnamon as part of a mix of healthy spices and its role in blood pressure, inflammation and risk of heart disease.

People have been finding ways to use cinnamon for thousands of years (it appears in Chinese writing from 4000 B.C.), so the possibilities for using it are vast. In Mexico, Ceylon cinnamon is used to flavor coffee or brewed as tea. In the Middle East and India, cinnamon is more likely to appear in savory dishes. Rogers suggested trying it as a rub to season chicken – or to spice up your morning oatmeal.

Rogers also likes cinnamon with nonfat vanilla yogurt. "I usually add berries and cinnamon to that because the cinnamon goes really nice with any kind of berry."

Of course, it's a favorite in holiday dishes and desserts. And while a sprinkling of cinnamon probably won't turn your favorite pie into a health food, Rogers helpfully noted that "desserts consumed in moderation are perfectly fine."

Eat It or Leave It? is an ľ¹ÏÖ±²¥ News series that takes a closer look at the health benefits and drawbacks of specific foods and drinks.