Quercetin in Onions Prevents Asthma, Allergies and Heart Disease
The known health benefits of onions may be fairly new but these flavorful bulbs have been a food staple for more than 3,000 years. This humble vegetable doesn’t get a lot of media hype compared to green tea, red wine and blueberries, but some scientists are saying onions may just be one of the greatest super foods yet.
Onions are a member of the allium family of plants – garlic, shallots, chives and leeks are in the same family – and the most common types are yellow, red and white. 
They are the second most important horticultural product grown in the world.
What truly makes the health benefits of onions so fantastic are the properties of the polyphenol quercetin compound. Polyphenols are phytochemicals, antioxidants that naturally protect plants against bacteria and viruses. Red wine, citrus, olive oil and apples also contain quercetin.
A Natural Anti-Inflammatory
Cornell University food science associate professor, Rui Hai Liu, MD, PhD, said, “Our study clearly shows that the health benefits of onions and shallots have potent…antioxidant activity and protective effect.” Cornell’s study was published in the Journal of Agricultural and Food Chemistry.
Liu continued, “Onions are one of the richest sources of flavonoids in the human diet. Flavonoids are not only anti-cancer but also are known to be antibacterial, antiviral, anti-allergenic and anti-inflammatory.”
Cornell Researchers found that quercetin is most abundant in yellow and red onions and shallots; white and sweet onions contain far lower quantities. Shallots and yellow onions contain the highest amount of quercetin while Vidalia (sweet) onions contain the least.
Health Benefits of Quercetin
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• Reduces allergic reactions with natural antihistamines
• Eases the swelling and joint stiffness of arthritis
• Improves the balance of good (HDL) cholesterol and bad (LDL) cholesterol
• Lowers your risk of all cancers and inhibits tumor growth
• Lowers risk of lung cancer in smokers
• Prevents heart disease
• Improves prostate health
• Reduces the severity of bladder infections
Allergies and asthma affect one in every five people in the United States. The health care costs alone are almost 8 billion annually. Quercetin stops your immune system from releasing histamines, easing allergen symptoms such as runny nose and watery eyes.
Quercetin also prevents plaque buildup on the arterial walls – plaque buildup is the primary cause of heart attack and stroke. It also protects against LDL cholesterol.
One study showed that quercetin – in combination with an alcohol-free red wine also containing this polyphenol – prevented dangerous cholesterol accumulation in overweight participants who were at risk for heart attack.
The health benefits of onions aren’t only due to the abundance of quercetin. Allyl propyl disulphide (APDS) is an anti-inflammatory sulfur compound also found in onions that gives them their distinct smell and makes your eyes water.
The combination of sulfur and quercetin fights twice as hard to bring down inflammation – what doctors and scientists believe is one of the major contributors to disease.
Health Benefits of Sulfur
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• Lowers blood sugar by triggering more insulin production to transport glucose
• Lowers high blood pressure
• Lowers LDL cholesterol
• Prevents blood clots that can lead to heart attack, stroke and hardening of the arteries
• Improves symptoms of asthma and other breathing problems
Onions are naturally salt and fat free, low in calories and abundant in vitamins C, B6, A and E. The copper found in onions protects your bones and joints, firms your skin and possibly prevents osteoporosis in women. Your bowels will also thank you, since onions encourage the growth of good gut bacteria that aids in digestion.
The nutritional rule of thumb: The stronger it smells or tastes, the higher the antioxidants.
Beat Cancer with These Winning Combinations
A study conducted by Johns Hopkins University School of Medicine paired the antioxidant power of onions with that of known cancer-fighter, turmeric. Curcumin, the cancer-fighting compound found in turmeric, gives curry its yellow color. Results showed that inherited precancerous cells in the bowels reduced in size and number.
By combining the antioxidants found in onions with bromelain, the active ingredient in pineapple, the anti-inflammatory and antihistamine effects are enhanced.
A Word of Caution
If you are currently on hormone replacement therapy (HRTs), too much quercetin can reduce the effectiveness of your medication. Some participants in studies complained of upset stomach. Bromelain should be taken for 8-10 days with an equal break of time before taking it again. Stomach upset, diarrhea and increased menstrual bleeding have been reported with long-term bromelain use.
As always, if you are pregnant or nursing you should speak to your doctor before increasing your intake of any nutrient. Sufficient studies have not been completed for pregnant women or children.
The health benefits of onions far outweigh potential bad breath. Inexpensive, flavorful and chock full of free radical fighters – adding this diverse vegetable into your daily diet is common sense for your total body health. 
