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Onion (yang cong)

What is onion? What is it used for?

The onion is a member of the lily family, and is related to garlic, chives, scallions and leeks. Like potatoes, onions grow underground.

They originated in Europe and Asia, but are now found worldwide, due in part to their legacy as a staple food; in fact, the name of the city "Chicago" is derived from an Indiana word used to describe the odor of onions.

Although onions have been used as food sources for centuries, they have a long tradition in herbal medicine as well. One of its original uses was as a treatment for tumors. It was also made into a type of syrup to suppress coughs, and prepared in a tincture (along with alcohol) to relieve edema. Today, onion is consumed more as a food and less as an herbal remedy.

Onion contains several active ingredients. The most well-known are a group of sulfur compounds, which form a strongly scented oil and are the reason most people "cry" when cutting onions. However, studies have shown that the oil also has strong antimicrobial properties, and may lower blood sugar levels in people with diabetes. The other active ingredients in onion are flavonoids, particularly quercetin. Quercetin has been linked to a decreased risk of heart attack and may reduce the incidence of atherosclerosis. Other evidence suggests that substances in onions and onion oil may prevent some forms of cancer, such as stomach cancer and breast cancer.

How much onion should I take?

Most studies on onion have shown that they can produce an effect when a person eats at least 25 grams per day; other studies have used two to four times that amount. Although some studies have found that cooked onions provide some healthy benefits, most suggest that the active ingredients are less potent when the onions are booked; as such, fresh or raw onions are considered the best for herbal remedies. If a patients is using an onion tincture, syrup or extract, the recommended dose is one tablespoon three times per day, but it may be necessary to take the dosage for several months before any difference is noted.

What forms of onion are available?

Fresh, raw onions are available at grocery stores worldwide. Dried onions are also available, as are onion tinctures, powders, syrups and extracts.

What can happen if I take too much onion? Are there any interactions I should be aware of? What precautions should I take?

While most people can eat onions without any difficulty, high onion intake can worsen existing cases of heartburn in some people. There have also been isolated reports of onions causing some allergies, which usually present as a skin rash and/or red, itchy eyes. It is safe for consumption by children and (in small amounts) women who are pregnant or breastfeeding, although women with heartburn may experience some discomfort. As of this writing, there are no known drug interactions with onions or onion oil. As always, make sure to consult with a licensed health care provider before taking onions or any other herbal remedy or dietary supplement.


  • Ali M, Bordia T, Mustafa T. Effect of raw versus boiled aqueous extract of garlic and onion on platelet aggregation. Prostaglandins Leukot Essent Fatty Acids 1999;60:43-7.
  • Onstad D. Whole Foods Companion: A Guide for Adventurous Cooks, Curious Shoppers and Lovers of Natural Foods. White River Junction, VT: Chelsea Green Publishing, 1996, pp. 202-206.
  • Rimm ER, Katan MC, Ascherio A, et al. Relation between intake of flavonols and risk for coronary heart disease in male health professionals. Ann Intern Med 1996;125:384-389.
  • Valdivieso R, Subiza J, Varela-Losada S, et al. Bronchial asthma, rhinoconjunctivitis, and contact dermatitis caused by onion. J Allergy Clin Immunol 1994;94:928-930.
  • Zohri AN, Abdel-Gawad K, Saber S. Antibacterial, antidermatophytic and antitoxigenic activities of onion (Allium cepa L.) oil. Microbial Res 1995;150:167-172.
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