Onion

Efficacy-safety rating:

●●...Ethno or other evidence of efficacy.

Safety rating:

What is Onion?

The onion plant is a perennial herb with hollow cylindrical leaves. On top of the long stalk are greenish-white flowers, and the seeds of the plant are black and angular. The underground bulb is used medicinally.

What is Onion used for?

Onions contain 89% water, 1.5% protein, and vitamins, including B1, B2, and C, along with potassium. Polysaccharides also are present, as are peptides, flavonoids, and essential oil. The alliums, like onion, contain alliin and similar sulfur compounds. Prostaglandins also have been identified in onion.

Central Asia is believed to be the region of origin of the onion. Onions were used as early as 5000 years ago in Egypt, as seen on ancient monuments. Ancient Greek and Roman recordings also refer to the onion. During the Middle Ages, onions were consumed throughout Europe. They later were thought to guard against evil spirits and the plague, probably because of their strong odor. Onion “skin” dye has been used for egg and cloth coloring for many years in the Middle East and Europe. Columbus was said to have brought the onion to America. Folk healers used the onion to prevent infection. The combination of onions and garlic cooked in milk is a European folk remedy used to clear congestion. In folk medicine also, onion has been used for asthma, whooping cough, bronchitis, and similar ailments. Onions also are used in homeopathic medicine.

The main properties of onion include antimicrobial activity, cardiovascular support, hypoglycemic action, antioxidant/anticancer effect, and asthma protection. More research is needed in the area of asthma treatment, although certain compounds are said to inhibit bronchoconstriction. The bulb contains certain sulfur compounds that are known to be antimicrobial. The onion also may be of benefit in cardiovascular disease, as it possesses hypolipidemic effects and has antiplatelet actions, retarding thrombosis. But certain lipid-reducing and blood pressure-lowering effects in humans have not yet been clinically proven. Some studies have been performed concerning diabetes treatment by onion with promising results in animal experimentation. Although more research is needed on the use of onion as a treatment for diabetes in humans, many articles describe onion's benefits in improving glucose levels. The onion also is a proven antioxidant and may be helpful in treating certain cancers. More clinical research is needed to understand the many medicinal benefits of onion.

Other reported uses include the treatment of stingray wounds, warts, acne, appetite loss, urinary tract disorders, and indigestion. These uses have not been proven.

What is the dosage of Onion?

Fresh onion bulbs are used at daily doses of 50 g. Dried onion is used at a dose of 20 g/day for dyspepsia.

Is Onion safe?

Contraindications have not yet been identified.

Generally recognized as safe when used as food. Avoid dosages above those found in foods because safety and efficacy are unproven.

While the German Commission E lists no interactions, there are some theoretical concerns. Theoretically, there may be a possible increased risk of bleeding because onion has some antiplatelet activity. Avoid concurrent use of warfarin medications because of theoretical additive or synergistic effects.

The German Commission E lists no contraindications, side effects, or interactions.

Certain sulfur compounds escape from the onion in vapor form and hydrolyze to sulfuric acid when it is cut, causing the familiar eye irritation and tearing. Corneal swelling from onion exposure has been reported. Using a sharp knife also minimizes the crushing of onion tissue and liberation of volatiles, and cutting an onion under running water avoids tearing. With large intake, the stomach may be affected, and frequent contact with onion rarely may cause allergic reaction.

The toxicity of large doses of onion has been unresolved.

References

Copyright © 2006 Wolters Kluwer Health

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