By Dr. Mercola
Eighty-seven percent of U.S. adults say they like onions,1 which is great news since they’re one of the healthiest foods you can eat. Rich in vitamin C, sulphuric compounds, flavonoids, and other phytochemicals,2 an onion a day may help keep the doctor away.
Onions are surprisingly high in beneficial polyphenols, which play an important role in preventing and reducing the progression of diabetes, cancer, and neurodegenerative and cardiovascular diseases.
Polyphenols also play an important role as a prebiotic, increasing the ratio of beneficial bacteria in your gut, which is important for health, weight management, and disease prevention.
Onions contain more polyphenols than even garlic or leeks, and are one of the best sources of a type of polyphenol called flavonoids, especially the flavonoid quercetin.
Onions Provide Disease-Fighting Quercetin
Quercetin is a powerful antioxidant with anti-inflammatory properties that may help fight chronic diseases like heart disease and cancer. In lab studies, quercetin was shown to prevent histamine release (histamines are the chemicals that cause allergic reactions.3
This makes quercetin-rich foods like onions “natural antihistamines.” In addition, quercetin may:4
Reduce the risk of atherosclerosis
Help prevent death from heart disease
Reduce blood pressure
Relieve symptoms of interstitial cystitis
Reduce symptoms of prostatitis
Inhibit the growth of cancer cells from breast, colon, prostate, ovarian, endometrial and lung tumors
Lower lung cancer risk, especially among smokers
While apples and tea also contain quercetin, onions appear to be a particularly good source. Research from Wageningen Agricultural University in the Netherlands showed quercetin absorption from onions is double that from tea and three times that from apples.5
Research from the University also showed consuming onions leads to increased quercetin concentrations in the blood. As reported by The World’s Healthiest Foods:6
“… [O]n an ounce-for-ounce basis, onions rank in the top