Parts Used & Where Grown
Like its close cousins garlic, chives, scallions, and leeks, onion is a member of the lily family (Liliaceae). It is native to Eurasia but now grows all over the world, due mostly to people bringing it with them as a staple food wherever they migrated. The French explorer Pere Marquette was saved from starvation in 1624 by eating wild onions near the present site of Chicago—the name of the city is derived from a Native American word for the odor of onions.1 The bulb of the plant is used medicinally.
Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
Type 2 Diabetes
2 to 3.5 ounces fresh onion daily
Onion may lower blood glucose levels and improve glucose tolerance in people with type 2 diabetes.
Onions have been used traditionally to treat diabetes. Animal studies suggest onion extracts may help reduce high blood glucose levels. Onion and its constituents have been shown in the laboratory to inhibit enzymes involved in the breakdown and digestion of starches and other carbohydrates, as well as enzymes involved in glucose metabolism. Onion has further been found to stimulate insulin responsiveness and glucose uptake by cells. Preliminary trials have found eating onions, in amounts of 60 and 100 grams (about 2 and 3.5 ounces) per day, lowered fasting blood glucose levels and the fasting response to glucose ingestion (glucose tolerance) in subjects with type 2 diabetes.
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Onion may act as an anti-inflammatory in people with asthma.
may act as an anti-inflammatory in people with asthma. Human studies have shown onion can be a strong anti-inflammatory. However, some people with asthma may experience an exacerbation of symptoms if they are allergic to onion and are exposed to it.
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Onion has a long history of use for relieving coughs.
The mucilage of slippery elm gives it a soothing effect for coughs. Usnea also contains mucilage, which may be helpful in easing irritating coughs. There is a long tradition of using wild cherry syrups to treat coughs. Other traditional remedies to relieve coughs include bloodroot, catnip, comfrey (the above-ground parts, not the root), horehound, elecampane, mullein, lobelia, hyssop, licorice, mallow, (Malvia sylvestris),red clover, ivy leaf, pennyroyal (Hedeoma pulegioides, Mentha pulegium),, (Allium cepa), and plantain (Plantago lanceolata, P. major). None of these has been investigated in human trials, so their true efficacy for relieving coughs is unknown.
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Onion injections into the skin and topical onion applications have been shown to inhibit skin inflammation in people with eczema, according to one trial.
injections into the skin and topical onion applications have been shown to inhibit skin inflammation in people with eczema, according to one double-blind trial. The quantity or form of onion that might be most effective is unknown.
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Onion is an herb that directly attack microbes.
Type 1 Diabetes
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Research in laboratory animals suggests onion and its active constituents may lower blood glucose levels, raise insulin levels, reduce advanced glycation end-product (AGE) formation, and possibly prevent diabetes complications.
Research in laboratory animals suggests onion and its active constituents may lower blood glucose levels, raise insulin levels, reduce advanced glycation end-product (AGE) formation, and possibly prevent diabetes complications. In one preliminary trial, people with type 1 diabetes had lower blood glucose levels four hours after eating about three ounces of raw onion than after receiving water.
Traditional Use (May Not Be Supported by Scientific Studies)
Onion has been used as food for many centuries.2 Onion was also a popular folk remedy, being applied to tumors, made into a syrup for relieving coughs, or prepared in a tincture (using gin) to relieve “dropsy” (heart failure–related edema).3 It was considered a weaker version of garlic by many herbal practitioners. Like garlic, onion has a longstanding but unsubstantiated reputation as an aphrodisiac.4
How It Works
How It Works
Two sets of compounds make up the majority of onion’s known active constituents—sulfur compounds, such as allyl propyl disulphide (APDS), and flavonoids, such as quercetin. Each of these groups of compounds has multiple medicinal actions.
The sulfur compounds form a strongly scented oil, particularly the compound known as thioproanal-s-oxide or lacrimatory factor. It is responsible for the tearing many people suffer while cutting onions.5 Onion and onion oil constituents have been repeatedly shown to kill various microbes in the test tube.6, 7 Studies have not been conducted in humans to determine whether onion is a useful antimicrobial agent.
APDS has been shown to block the breakdown of insulin by the liver and possibly to stimulate insulin production by the pancreas, thus increasing the amount of insulin and reducing sugar levels in the blood.8 Several uncontrolled human studies9, 10 and at least one double-blind clinical trial11 have shown that large amounts of onion can lower blood sugar levels in people with diabetes. Onion does not reduce blood sugar levels in healthy nondiabetic people.12
Sulfur compounds in onion oil have also been shown to be anti-inflammatory, both by inhibiting formation of thromboxanes and by inhibiting the action of platelet-activating factor (PAF).13, 14 Not all studies have confirmed that these actions occur in humans.15 The anti-inflammatory effect is strong enough that subcutaneous onion injections and topical onion applications inhibit skin reactions to intensely inflammatory compounds in people with or without eczema, according to the results of one double-blind study.16 Human studies have not been performed to determine whether onion would be useful in people with asthma or cough, though the anti-inflammatory action cited above suggests it might be. These actions, coupled with an ability to reduce the stickiness of platelets17 and, overall, to decrease the thickness of the blood,18 have led to interest in onion as a way to prevent or possibly reduce atherosclerosis.
Human studies have proven mixed as to whether onion is helpful for people with atherosclerosis.19 Intake of quercetin in the diet, primarily from onion, tea, and apples, has been linked to a decreased risk of having a heart attack.20 High intake of quercetin and other flavonoids from onion and other foods has been shown to decrease risk of atherosclerosis in an epidemiologic study in the United States, although the result was not considered statistically significant.21 One open clinical trial showed that a crude onion extract could lower blood pressure in some people with hypertension.22 On the whole, it is unclear whether or not onion supplements, as opposed to onions eaten as food, have a beneficial effect on heart disease.
In a preliminary study of healthy male volunteers, administration of 50 grams of raw or boiled onion prevented the rise in serum cholesterol induced by consumption of a high-fat meal.23
The evidence on cancer prevention with onion suggests a benefit for some but not necessarily for all types of cancer. Onion consumption at a level of at least half an onion a day was associated with a 50% decline in stomach cancer risk in one study.24 Higher onion intake was also correlated with lower risk of breast cancer in a French epidemiological study.25 No protective effect against colorectal cancer was seen from higher onion intake.26
How to Use It
Most human studies that have shown an effect from onions used at least 25 grams per day and often two to four times that amount.27, 28 Though some studies have found cooked onions acceptable, several studies suggest that onion constituents are degraded by cooking and that fresh or raw onions are probably most active.29, 30, 31, 32
Interactions with Supplements, Foods, & Other Compounds
Interactions with Medicines
Most people can eat onion in food without any difficulties. Higher intakes of onion may worsen existing heartburn, though it does not seem to cause heartburn in people who do not already have it.33 There are also isolated reports of allergy to onion, including among people with asthma,34manifesting as skin rash and red, itchy eyes.
Onion is safe for use in children and, in small amounts in food, during pregnancy (though some pregnant women may have heartburn that onions could exacerbate) and nursing. It is unknown whether larger amounts of onion are safe during pregnancy and nursing. One study did find that baby rats nursing from mothers that were fed onion developed a taste for onion and suffered no ill effects.35
1. Onstad D. Whole Foods Companion: A Guide for Adventurous Cooks, Curious Shoppers & Lovers of Natural Foods. White River Junction, VT: Chelsea Green Publishing Co, 1996:202-6.
2. Onstad D. Whole Foods Companion: A Guide for Adventurous Cooks, Curious Shoppers & Lovers of Natural Foods. White River Junction, VT: Chelsea Green Publishing Co, 1996:202-6.
3. Felter HW, Lloyd JU. King's American Dispensatory, 18th ed, vol 1. Portland, OR: Eclectic Medical Publications, 1898, 1983:146.
4. Onstad D. Whole Foods Companion: A Guide for Adventurous Cooks, Curious Shoppers & Lovers of Natural Foods. White River Junction, VT: Chelsea Green Publishing Co, 1996:202-6.
5. Brodnitz MH, Pascale JV. Thiopropanal S-oxide: A lachrymatory [sic] factor in onions. J Agric Food Chem 1971;19:269-72.
6. Zohri AN, Abdel-Gawad K, Saber S. Antibacterial, antidermatophytic and antitoxigenic activities of onion (Allium cepa L.) oil. Microbiol Res 1995;150:167-72.
7. Kim JH. Anti-bacterial action of onion (Allium cepa L.) extracts against oral pathogenic bacteria. J Nihon Univ Sch Dent 1997;39:136-41.
8. Sharma KK, Gupta RK, Gupta S, Samuel KC. Antihyperglycemic effect of onion: Effect on fasting blood sugar and induced hyperglycemia in man. Indian J Med Res 1977;65:422-9.
9. Jain RC, Sachdev KN. A note on hypoglycemic action of onion in diabetes. Curr Med Pract 1971;15:901-2.
10. Mathew PT, Augusti KT. Hypoglycaemic effect of onion, Allium cepa Linn, on diabetes mellitus, a preliminary report. Indian J Physiol Pharmacol 1975;19:231-7.
11. Tjokroprawiro A, Pikir BS, Budhiarta AA, et al. Metabolic effects of onion and green beans on diabetic patients. Tohoku J Exp Med 1983;141:671–6.
12. Sharma KK, Gupta RK, Gupta S, Samuel KC. Antihyperglycemic effect of onion: Effect on fasting blood sugar and induced hyperglycemia in man. Indian J Med Res 1977;65:422-9.
13. Dorsch W, Ettl M, Hein G, et al. Anti-asthmatic effects of onions: inhibition of platelet-activating factor-induced bronchial construction by onion oils. Int Arch Allergy Appl Immunol 1987;82:535-6.
14. Dorsch W, Wagner H, Bayer T, et al. Antiasthmatic effects of onions: Alk(en)ylsulfinothic acid alk(en)ylesters inhibit histamine release, leukotriene and thromboxane biosynthesis in vitro and counteract PAF- and allergen-induced bronchial obstruction in vivo. Biochem Pharmacol 1988;37:4479-85.
15. Srivastava KC. Effect of onion and ginger consumption on platelet thromboxane production in humans. Prostaglandins Leukot Essent Fatty Acids 1989;35:183-5.
16. Dorsch W, Ring J. Suppression of immediate and late anti-IgE-induced skin reactions by topically applied alcohol/onion extract. Allergy 1984;39:43-9.
17. Chen JH, Chen HI, Tsai SJ, Jen CJ. Chronic consumption of raw but not boiled Welsh onion juice inhibits rat platelet function. J Nutr 2000;130:34-7.
18. Kendler BS. Garlic (Allium sativum) and onion (Allium cepa): A review of their relationship to cardiovascular disease. Prev Med 1987;16:670-85 [review].
19. Kleijnen J, Knipschild P, Ter Riet G. Garlic, onion and cardiovascular risk factors: A review of the evidence from human experiments with emphasis on commercially available preparations. Br J Clin Pharmacol 1989;28:535-44.
20. Hertog MGL, Feskens EJM, Hollman PCH, et al. Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study. Lancet 1993;342:1007-11.
21. Rimm EB, Katan MB, Ascherio A, et al. Relation between intake of flavonoids and risk for coronary heart disease in male health professionals. Ann Intern Med 1996; 125:384-9.
22. Louria DB, McAnally JF, Lasser N, et al. Onion extract in treatment of hypertension and hyperlipidemia: A preliminary communication. Curr Ther Res 1985;37:127-31.
23. Sharma KK, Chowdhury NK, Sharma AL, Misra MB. Studies on hypocholestraemic activity of onion. I. Effect on serum cholesterol in alimentary lipaemia in man. Indian J Nutr Diet 1975;12:288-91.
24. Dorant E, van der Brandt PA, Goldbohm RA, Sturmans F. Consumption of onions and a reduced risk of stomach carcinoma. Gastroenterology 1996;110:12-20.
25. Challier B, Perarnau JM, Viel JF. Garlic, onion and cereal fibre as protective factors for breast cancer: A French case-control study. Eur J Epidemiol 1998;14:737-47.
26. Dorant E, van den Brandt PA, Goldbohm RA. A prospective cohort study on the relationship between onion and leek consumption, garlic supplement use and the risk of colorectal carcinoma in the Netherlands. Carcinogenesis 1996;17:477-84.
27. Tjokroprawiro A, Pikir BS, Budhiarta AA, et al. Metabolic effects of onion and green beans on diabetic patients. Tohoku J Exp Med 1983;141:671–6.
28. Jain RC, Sachdev KN. A note on hypoglycemic action of onion in diabetes. Curr Med Pract 1971;15:901-2.
29. Bordia T, Mohammed N, Thomson M, Ali M. An evaluation of garlic and onion as antithrombotic agents. Prostaglandins Leukot Essent Fatty Acids 1996;54:183-6.
30. Tjokroprawiro A, Pikir BS, Budhiarta AA, et al. Metabolic effects of onion and green beans on diabetic patients. Tohoku J Exp Med 1983;141:671–6.
31. Chen JH, Chen HI, Tsai SJ, Jen CJ. Chronic consumption of raw but not boiled Welsh onion juice inhibits rat platelet function. J Nutr 2000;130:34-7.
32. 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.
33. Allen ML, Mellow MH, Robinson MG, Orr WC. The effect of raw onions on acid reflux and reflux symptoms. Am J Gastroenterol 1990;85:377-80.
34. Valdivieso R, Subiza J, Varela-Losada S, et al. Bronchial asthma, rhinoconjunctivitis, and contact dermatitis caused by onion. J Allergy Clin Immunol 1994;94:928-30.
35. Wuensch KL. Exposure to onion taste in mother's milk leads to enhanced preference for onion diet among weanling rats. J Gen Psychol 1978;99(2d Half):163-7.
Last Review: 06-05-2015
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The information presented by TraceGains is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2022.