Researchers and doctors disagree about whether vitamin C can prevent colds or chase away other illnesses, but vitamin C-rich citrus fruits are a sure cure for the winter blahs.

Oranges, tangerines and grapefruits are traditional favorites for snacking during the winter months. They also find their way into many cold-weather recipes. The tangy aroma of lemon chicken or orange-spiced tea can brighten up even the coldest, dreariest day of winter.In many ancient civilizations, oranges were thought to have magical properties, according to "Cooking with Sunshine: Recipes from the Sunkist Kitchens" (Atheneum).

Citrus fruits were believed to cure fevers, colic, dehydration, scorpion stings and other maladies.

Medieval sailors discovered that lemons, limes and other citrus fruits could prevent and cure scurvy, a condition caused by a deficiency of vitamin C.

The idea that the nutrient could prevent colds originated with two-time Nobel Prize winner Linus Pauling. Pauling, a renowned chemist, also recommends using vitamin C with chemotherapy for treating most cancers.

He advises that healthy people take between 6 and 18 grams of vitamin C daily, 100 to 300 times the U.S. Recommended Daily Allowance of 60 milligrams of the nutrient.

"When used properly and taken in time, vitamin C can prevent colds," said Dorothy Munro, one of Pauling's assistants at the Linus Pauling Institute of Science and Medicine in Palo Alto, Calif.

"If you take it at the first sign of a sniffle, it definitely can help. If you wait until the cold has set in, though, it won't help.

"Dr. Pauling gets a number of letters from people all the time who say things like `I haven't had a cold in years since I started taking vitamin C,' so it must be working."

However, several studies performed in the United States and Canada on the effects of large doses of vitamin C have failed to find a link between the nutrient and cold prevention, said Calvin Long, director of research for Baptist Medical Centers in Birmingham, Ala.

"The data thus far shows that there is no difference in the incidence of colds or in decreasing the amount of time that one shows the symptoms of colds," Long said.

"The difference in the incidence of colds for people taking large doses of vitamin C compared to those who did not was 0.09 percent, which is insignificant.

"Probably if there is any kind of positive response from people taking orange juice, it's just in general terms of good nutrition. Keeping the body in positive balance of nutrients is probably the best cure in terms of what we know about the common cold."

During the winter, many people take vitamin C supplements as preventive medicine.

Most people buy either the 500 milligram or 1,000 milligram dosages.

When a person takes that much vitamin C, though, most of it gets washed right out of the body within the day, Long said. Vitamin C is water-soluble, so the body cannot store large amounts.

"The more vitamin C you take, it's just a matter of excretion or reabsorption through the kidneys," he explained.