NEW YORK — Mighty enough to keep vampires at bay, garlic has for thousands of years been considered a wondrous substance, used to treat all sorts of ailments.

Its real powers are less certain, though studies continue into the possibilities that garlic can help lower blood pressure and cholesterol, act as a painkiller and an antibiotic, and help fight cancer.

Some studies of garlic and heart disease included too few people, said Nancy Ernst, a nutritionist with the National Heart, Lung and Blood Institute of the National Institutes of Health.

She also pointed out that because of garlic’s odor, it’s hard to do a “double-blind” study in which participants don’t know whether they’re getting the real thing. And some studies used high doses of garlic, 10 or more cloves a day.

“I think it would be a problem to suggest that people could get adequate cholesterol-lowering just by adding garlic to their diet,” Ernst said.

“I think we just really don’t know,” she said. “I think it would be useful to have an answer, so people don’t think it has magical powers.”

Several researchers are studying the effects on cancer of garlic and onions, or allium vegetables.

“Animal and in vitro experiments indicate that compounds in allium vegetables inhibit several types of tumors and decrease tumor growth and proliferation,” according to a study in the Journal of the National Cancer Institute last year, which found a reduction in stomach cancer risk among people in a province of China who regularly ate garlic and onions compared with those who did not.

Michael Wargovich of the M.D. Anderson Cancer Center in Houston said the research so far “clearly supports that the protective chemicals (from foods) will have to be part of the diet throughout life.”

Eventually, he said, food manufacturers may produce “designer foods” that include high doses of food components found to prevent cancer. But for now, he said, he and his wife “just try to follow the guidelines that are out there right now.”

“We don’t know even as researchers how much is enough,” he said.

Regardless of medical uses, garlic enhances the flavors of many foods. A raw clove has just four calories. Garlic contains almost no sodium or fat, but has some fiber and protein.

It can make some people ill. Of course, most people don’t eat but a little, although roasted garlic heads have become a popular appetizer. Roasting, or any cooking, reduces garlic’s pungency. It’s not certain how cooking garlic affects its medical potential.

Raw cloves can be sliced or smashed or forced through a press. Whole cloves can be sauteed to flavor oil, but if they burn they taste bitter. They also can be kept in vinegar to flavor it.

Chewing fresh parsley helps counteract the bad breath garlic causes.

When buying garlic, look for firm heads with tight skin. It should be stored in a cool, dark, ventilated place. Except in very humid, hot climates, it should not be refrigerated.

Folk medicine and lore long have depended on garlic to fight vampires, cholera, scorpion stings, leprosy and much more.

The journal Preventive Medicine pointed out that a 35-century-old Egyptian document considered garlic useful for treating heart disorders. Slaves building the Egyptian pyramids were said to have eaten great quantities of garlic. Romans thought it an aphrodisiac. Garlic juice was used on bandages to fight infections during World War I.

“Part of it is just myth. You could see if someone had garlic around their necks to ward away colds, maybe people just didn’t get in close enough contact” to be susceptible, Ernst suggested.

But much of it is not myth.

Eric Block, an organic chemist at the State University of New York, has been researching garlic and onions as possible agents in the treatment of heart disease and has found and patented a compound from garlic called ajoene that is “a pretty potent inhibitor” of the formation of blood clots, as effective as aspirin, he said.

“The garlic and onion were like detective stories waiting to be approached by a sleuth,” Block said.

His laboratory work has yet to be tested on animals or people, but Block said he has no doubts about garlic’s power. In fact, one indicator of its power — bad breath — has kept him from testing his theories on himself.

“I’m a department chairman and I have to do a lot of negotiating with parents, students, faculty,” he said. “It’s a social problem.”