The scholar Ibn al-Qayyim described some of the health benefits of onions in his great work "The Prophetic medicine." He said that onions were beneficial for expelling toxic odors from the body, cleansing the stomach and improving complexion.

He specifically mentioned the benefits of onion seeds for:

• The treatment of leukoderma (a chronic skin disease that causes loss of pigment, resulting in irregular pale patches of skin);
• Effective against alopecia when applied as an ointment;
• Mixing onion seeds with honey and using as a kohl for the treatment of leucoma (an eye disease consisting of an opaque white spot on the cornea).

Ibn-al Qayyim also mentioned applying onion juice in the ear to treat ear and hearing problems. He said that cooked onion was beneficial for jaundice and a cough.

One of the drawbacks he mentioned of eating raw onion was that it can cause bad breath, but these effects could be eliminated by cooking the onion.

What Are onions?

Onions are a member of the lily family and there are two basic types:

• Bulb-forming: these are the onions commonly used in cooking, and consist of many varieties including white, yellow and Spanish onions.
• Perennial: these are clusters of onions that can be replanted to produce another crop of onions.

Onions contain quercetin, a powerful flavonoid antioxidant. Onions are an excellent source of fiber, Vitamin C and folate. Phytochemicals found in onions, particularly allyl sulfides, appear to reduce the risk of some cancers.

Some of the health benefits of onions found in recent studies include:

• Cancer: Yellow onions were found to contain the third highest level of phenolic (a type of antioxidant), of all vegetables in an American study, and were fourth highest in anticancer-growth activity.

• Lung Cancer: onions are rich in the phytochemical quercetin, and a study showed the beneficial effects this has on lung cancer; people who increased their onion consumption decreased their risk of developing lung cancer.

• Colon and Liver Cancer: researchers at Cornell University found that stronger-tasting onions were more effective at inhibiting the growth of liver and colon cancer cells than milder-tasting onions.

• Heart Health: Allyl sulfides, found in onions, decrease the tendency of blood clots to form, which can significantly lower LDL cholesterol levels. A study of Japanese women found that those with the highest onion intake had the lowest LDL cholesterol. Another study, conducted at the University of Wisconsin-Madison found that stronger-tasting and stronger-smelling onions made blood platelets less sticky, therefore reducing the risk of atherosclerosis, cardiovascular disease, heart attack and stroke.

Tip on Using Onions

• Avoid onions that are soft, whose skin is wet, or that are sprouting.

• Onions do not have to be eaten raw to obtain maximum health benefits; quercetin is relatively stable while being cooked so retains its powerful effects.

• Cooking onions gives them a sweeter taste, and prolonged heat causes the sugars to brown the onion, known as caramelizing.

• Slicing an onion causes its cell walls to tear, which releases a sulfur compound called propanethial S-oxide, and this can cause eye irritation. This effect can be reduced by placing the onion in the refrigerator an hour before cutting. Cutting an onion under running water can also reduce irritation to the eyes.

References for further reading

• Arai Y, Watanabe S, Kimira M, Shimoi K, Mochizuki R, Kinae N. Dietary intakes of flavonols, flavones and isoflavones by Japanese women and the inverse correlation between quercetin intake and plasma LDL cholesterol concentration. J Nutr. 2000 Sep; 130(9):2243-2250.

• Chu YF, sun J, Wu X, Liu RH. Antioxidant and antiproliferative activities of common vegetables. J Agric Food Chem. 2002 Nov 6;50(23):6910-6916.

• Craig WJ. Phytochemicals: Guardians of our health. J Am diet Assoc. 1997;97: S199-S204.

• Dole nutrition Institute. "Onions Boost bone health." 2005. Available at: www.dolenutrition.com. Accessed 5/18/06.

• Grant WB. A multicountry ecologic study of risk and risk reduction factors for prostate cancer mortality. Eur Urol. 2004 Mar;45(3):271-279.

• Knekt P et al. Flavonoid intake and risk of chronic diseases. Am J Clin Nutr. 2002 Sep;76(3):560-568.

• Le Marchand L, Murphy SP, Hankin JH, Wilkens LR, Kolonel LN. Intake of flavonoids and lung cancer. J Natl cancer Inst. 2000 Jan 19;92(2):154-160.

• Onion extract gel versus petrolatum emollient on new surgical scars: prospective double-blinded study. Dermatol Surg. 2006 Feb;32(2):193-197.

• Osmont KS, Arnt CR, Goldman IL. Temporal aspects of onion-induced antiplatelet activity. Plant Foods Hum Nutr. 2003 Winter;58(1):27-40.

• Yang J, Meyers KL van der Heide J, Liu RH. Varietal differences in phenolic content and antioxidant and antiproliferative activities of onions. J Agric Food Chem. 2004 Nov 3;52(22):6787-6793.