Botanical name: Allium cepa
© Martin Wall
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.
Onion has been used in connection with the following conditions (refer to the individual health concern for complete information):
|Science Ratings||Health Concerns|
Reliable and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.
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
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
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 If a tincture, syrup, or oil extract is used, 1 tablespoon three times per day may be necessary for several months before effects are noted.33
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.34 There are also isolated reports of allergy to onion, including among people with asthma,35 manifesting 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.36
At the time of writing, there were no well-known drug interactions with onions.
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(suppl):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, onions 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 [review].
20. Hertog MGL, Feskens EJ, Hooman PC, et al. Dietary antioxidant flavonoids and the risk of coronary heart disease: The Zutphen Elderly Study. Lancet 1993;342:1007–11.
21. Rimm ER, Katan MB, Ascherio A, et al. Relation between intake of flavonols and risk for coronary heart disease in male health professionals. Ann Intern Med 1996;125:384–9.
22. Louria DB, McAnally JF, Lasser N, et al. Onion extract in treatment of hypertension and hyperlipidemia: A preliminary communication. Curr Ther Res 1985;37:127–131.
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(suppl):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(suppl):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. Louria DB, McAnally JF, Lasser N, et al. Onion extract in treatment of hypertension and hyperlipidemia: A preliminary communication. Curr Ther Res 1985;37:127–131.
34. 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.
35. 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.
36. 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.
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The information presented in Healthnotes 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 September 2008.