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Onion (Allium cepa)

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Also listed as: Allium cepa
Related terms
Background
Evidencetable
Tradition
Dosing
Safety
Attribution

Related Terms
  • Allicepin, allicin, alliin, Allium cepa, Allium cepa L., allium vegetables, allylsulfides, apigenin, anthocyanins, botanicals, caffeic acid, cinnamic acids, cycloalliin, cysteine, diallyl disulfide, dipropyl disulfide, green onion, isoquercetin, isorhamnetin, kaempferol, L-cysteine sulfoxide, lignans, Liliaceae (family), luteolin, myricetin, onion extract, onion juice, onion powder, onion vinegar, organosulfur compounds, p-hydroxybenzoic acid, phytoestrogens, pickling onions, protocatechuic acid, quercetin, quercetin diglucoside, quercetin monoglucoside, red onion, rutin, S-alk(en)yl cysteine sulfoxides, S-allylcysteine, selenium, Spring Sweet, Sweet Imperial, syn-propanethial-S-oxide, taxifolin, Texas Grano 438, thiosulfinates (allyl methyl trisulfide, diallyl sulfide), Ultra Hybrid, vanillic acid, Vidalia onions, Walla Walla, white onion.
  • Note: Onion (Allium cepa) should not be confused with plants of the Zigadenus species.

Background
  • Onion (Allium cepa L.) is widely used around the world as a food product and has also been used for medicinal applications.
  • Most of the available research has focused on scar prevention, but the results are mixed in this area. Onion has been used in the treatment of diabetes, cancer, heart disease, and alopecia areata (hair loss).
  • As onion is a commonly consumed food, it is considered likely safe in smaller amounts, although there are reports of skin rash and gastrointestinal problems in sensitive individuals.

Evidence Table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. GRADE *


Early study suggests that application of an alcoholic onion extract on the skin may reduce allergic responses, such as wheals ("hives") and flares. More research is needed in this area.

C


Study using topical onion juice increased hair regrowth in alopecia areata (hair loss) patients, especially women. More research is needed in this area to confirm these results.

C


Early evidence suggests that onion or onion extract prevents cancer, including gastrointestinal, ovarian, skin, and endometrial cancers. Some studies, however, have reported no association between Allium vegetable consumption and incidence of cancer (particularly breast and lung cancer). More research is needed before a conclusion can be made.

C


One clinical trial found that fresh onion significantly decreased serum glucose (blood sugar) levels in diabetics. More research is needed in this area to confirm these results.

C


Early evidence suggests that consumption of onions and other vegetables belonging to the Allium genus may reduce the risk of heart attack. More well designed studies are needed before a conclusion can be made.

C


Onion-olive oil capsules may help lower blood pressure, although additional research is needed to make a firm conclusion.

C


Research in humans found that onion may have an effect on blood serum triglyceride, betalipoprotein cholesterol and phospholipid levels. More research is needed in this area to confirm these results.

C


Several trials have been conducted using combination products that include an onion extract. These studies have investigated onion's potential role in scar healing in adults and children, specifically due to injuries from laser tattoo removal or surgery. The overall results are mixed, and more research is needed to make a conclusion.

C
* Key to grades

A: Strong scientific evidence for this use
B: Good scientific evidence for this use
C: Unclear scientific evidence for this use
D: Fair scientific evidence for this use (it may not work)
F: Strong scientific evidence against this use (it likley does not work)


Tradition / Theory

The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.

  • Aging, anthelmintic, antibacterial, antifungal, anti-inflammatory, antimicrobial, antimutagenic, antioxidant, antiparasitic, antiplatelet (blood thinning), antiseptic, antiviral, arthritis, asthma, atherosclerosis (hardening of the arteries), baldness, bee stings, behavior (animal), benign prostatic hypertrophy (BPH), cataract, chilblains (inflammation of the hands and feet caused by exposure to cold and moisture), conjunctivitis, convulsions, coronary heart disease, cough, depression, diabetic nephropathy, digestion (prebiotic), digestive stimulant, exercise recovery, eye diseases (loa loa), eye inflammation, food preservative, gastrointestinal disorders, gout, hemophilia, immune enhancement, influenza, insecticidal, insomnia, irritable bowel syndrome (IBS), kidney dysfunction, leukemia, lice, liver protection, malaria, memory enhancement, neonatal disorders (asphyxia), neurodegenerative disorders, neuroprotection, obesity, osteoporosis, prostate conditions, scurvy, sinusitis, soft tissue injury (torn ligaments and tendons), sore throat, spermatogenesis, sun protection, tardive dyskinesia, thrombosis (blood clot), thyroid disorders, wound healing, wounds (stingray), yeast infections.

Dosing

Adults (over 18 years old)

  • There is currently no proven effective medicinal dose of onion in adults.
  • For diabetes, a diet supplemented with 20 grams of fresh onion three times daily has been taken by mouth.
  • For high blood pressure, four onion-olive oil maceration capsules have been taken by mouth daily for one week.
  • For scars, the following has been used: Mederma® (Merz Pharmaceuticals, Greensboro, NC, USA) applied to the skin three times daily for eight weeks; an onion gel extract applied to the skin three times daily for one month or for 10 weeks; Contractubex® gel (10% onion extract, 50IU of sodium heparin per gram of gel, and 1% allantoin) rubbed into scars 1-4 times daily for up to six months.
  • For alopecia areata, Australian brown onion juice has been applied to areas of hair loss twice daily for two months.
  • For determination of allergies, onion juice solution in 45% ethanol has been injected into the skin followed by an undiluted onion solution being applied to the skin at the injection sites.

Children (under 18 years old)

  • There is currently no proven safe or effective medicinal dose of onion in children.
  • For scars, Contractubex® gel (10% onion extract, 50IU of sodium heparin per gram of gel, and 1% allantoin) has been rubbed into scars 1-4 times daily for up to six months.

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

  • Avoid in individuals with a known allergy or hypersensitivity to onion (Allium cepa) or its constituents. In some individuals, handling onion bulbs has caused skin rash, painful tingling in the fingers, or a reddening of the skin.

Side Effects and Warnings

  • Onion is likely safe when consumed in food amounts and when onion extract is applied to the skin for scar healing.
  • The primary adverse effects associated with onion are dermatologic (pemphigus, a chronic blistering disease, and skin rash) and gastrointestinal (heartburn, dyspepsia (upset stomach), gastric acidity, and gastroesophageal reflux). Swelling and ulceration of the eye have been reported from handling onion. Bronchial asthma from onion has been reported in children. Large amounts of onion may have toxic effects. Some studies have demonstrated contamination of onion with antibiotics, heavy metals, and microbes.
  • Onion should be used cautiously in patients with hematologic (blood) disorders or taking anticoagulants or antiplatelets (blood thinners), in patients with diabetes or hypoglycemia (high or low blood sugar) or taking agents that affect blood sugar, and in patients with hypotension (low blood pressure) or taking agents that lower blood pressure. In clinical studies, onion has been found to lower blood pressure in both patients with and without hypertension (high blood pressure).
  • Use cautiously in patients with gastrointestinal disorders as onion may worsen some conditions.
  • Use cautiously in patients with high cholesterol since although most studies suggest that onion may have favorable effects on cholesterol levels, some studies have found that onion may increase cholesterol.
  • Use cautiously in patients with or prone to cancer, since in limited study onion was associated with an increased risk of colon and stomach cancer.
  • Onion may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be decreased in the blood, and reduce the intended effects. Patients taking any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
  • Use cautiously with p-glycoprotein substrates or cyclosporine.
  • Avoid in patients who are allergic or hypersensitive to onion or plants in the Lilaceae family. Anaphylaxis has been reported in sensitive individuals. Work-related allergy has been reported.
  • Avoid if pregnant or breastfeeding in medicinal doses.

Pregnancy and Breastfeeding

  • Onion, in medicinal amounts, is not recommended in pregnant or breastfeeding women due to a lack of available scientific evidence.

Attribution
  • This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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