Allium cepa is the common onion. Although it is usually thought of as a vegetable, A. cepa also has a long history of medicinal use.
Onions are perennials that are cultivated for food worldwide. There are many varieties. Most onion bulbs are white, yellow, or red. The green stems and leaves are hollow and can reach 3 ft (1 m) in height. The plants bear small flowers that are usually white or purple. The fleshy bulb that grows below the ground is used medicinally as well as for food. Onions are members of the lily family.
Onion has been used as a food source for almost as long as humans have been keeping written records. Their usefulness has been discovered independently by many cultures on several continents. Onions are mentioned in ancient Egyptian
writings and were known in ancient Greece. In medieval Europe, they were used unsuccessfully to ward off plague.
In North America, Native Americans used onion to treat insect stings and relieve colds. It is also used in traditional Chinese medicine. Homeopaths make a tincture of onion to treat a variety of conditions including cold, cough, diarrhea, facial paralysis, hay fever, hernia, laryngitis, pneumonia, and trauma.
Over the centuries, onion has been used for healing both internally and externally. Internally, onion has been recommended to treat colds, cough, bronchitis, whooping cough, asthma, and other respiratory problems. It is believed to help loosen congestion in the lungs and expand the airways.
Onion is also used internally to relieve excess gas and calm an upset stomach. A mixture of rue (Ruta graveolens) and onion is used to rid the digestive system of parasites. Onion is also thought to stimulate the appetite.
Onion is believed to have a positive effect on the circulatory system. It has been used as a diuretic to reduce swelling. It is also thought to help reduce arteriosclerosis by lowering blood cholesterol levels and preventing the formation of blood clots. Onion has been used to treat diabetes and is reputed to lower blood sugar levels.
Externally, fresh onion juice is used to prevent bacterial and fungal infections. It can be applied to wounds and stings on the skin, used to remove warts, used to stimulate hair growth, and even used to reduce unwanted skin blemishes. Warm onion juice dropped in the ear is said to help relieve earache. Baked onion is used to draw pus from abscesses.
Modern scientific research supports many of the traditional uses for onion. Onion contains thiosulphinate, a compound that is effective in killing many common bacteria, including Salmonella typhi, Pseudomonas aeriginosa, and Escherichia coli. This finding supports the folk use of onion to treat wounds and skin infections and possibly its use for an upset stomach.
Even more supportive are small clinical studies on humans that show that both fresh onions and commercial onion extracts actually lower blood cholesterol levels, lower blood pressure and help prevent the formation of blood clots. Although these studies have been done on only a small number of people, they are consistently supported by additional data from animal and test-tube studies.
In 1990, scientists detected the presence of a compound in onion that partially blocks the development of inflammation. In addition, laboratory animals were protected against induced asthma with fresh onion juice. Humans with asthma have also shown reduced allergy-induced constriction of the airways when given an extract of onion. These findings support the traditional folk administration of onion to treat asthma and respiratory complaints.
Some test-tube and small animal studies suggest that onion oil can stop the growth of tumors. Whether these results are applicable to humans remains to be seen, but in a 1989 study done in China, people who ate large amounts of vegetables in the Allium family appeared to have a significantly reduced rate of stomach cancer.
Onion has also been shown to contain antioxidants, which are compounds that protect the body against free radicals. Free radicals are highly reactive molecules that destabilize other molecules and are associated with a number of degenerative diseases.
The German Federal Health Agency's Commission E, established in 1978 to independently review and evaluate scientific literature and case studies pertaining to herb and plant medications, has approved onion as an antibacterial agent. Although many studies are promising, more information is needed before this endorsement is extended to other uses of onion. In general, however, it appears that onion is a healthful vegetable that may confer many medical benefits.
Onion is a common vegetable, and can be served cooked or raw. For medicinal purposes, onion is available for internal use as a capsule or tablet containing dehydrated onion or onion extract. A recent study of the antioxidant activity of onion juice indicates that it is not affected by heating or boiling. For external use, the juice of fresh onion is used. A common dose is 1/4–1 cup of raw onions daily or one teaspoon of juice three times a day. In folk medicine, a cough syrup is made of raw onion liquid and honey.
No special precautions are needed when taking onion medicinally.
Although no allergic reactions to the bulb of the onion are reported, some people develop an allergic rash after handling the leaves of the plant. In addition, windblown particles of onion leaves and skin have been shown to irritate the eyes of farm workers employed to harvest the onions.
There are no studies of the interaction of onion and conventional pharmaceuticals. However, given the long and widespread use of onion as a vegetable, serious interactions appear unlikely.
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Hwang, Y. H., et al. "Suspended Onion Particles and Potential Corneal Injury in Onion Harvesters." Archives of Environmental Health 57 (January-February 2002): 78-84.
Racchi, M., et al. "Antiradical Activity of Water-Soluble Components in Common Diet Vegetables." Journal of Agricultural and Food Chemistry 50 (February 2002): 1272-1277.
Rebecca J. Frey, PhD