Foods High in Quercetin

The flavonoid quercetin may help keep people's hearts healthy while fighting inflammation and cancer. Flavonoids are antioxidants found in fruits and vegetables, and the chemicals defend the body and its processes. Quercetin may also help prevent ulcers, cataracts and allergies. Most people already consume anywhere from 5 to 70 mg daily of quercetin, according to Vitamin Retailer, a dietary supplement industry magazine. The magazine recommends people ingest 400 mg three times per day.

Apples

• Apples contain high amounts of antioxidants, including quercetin. Health expert Dr. Andrew Weil recommends eating organic apples since the Environmental Working Group includes the fruit in its so-called "dirty dozen"--the fruits most contaminated by pesticides.

  The skins of apples hold most of the fruit's antioxidants, and some types of apples contain more healthful compounds than others. Red Delicious, Ida Red and Northern Spy apples rank as the healthiest. Dr. Weil also says that the quercetin found in apples can help improve memory and may help ward off Alzheimer's disease. For optimum absorption, eat an apple a day.

Tea

• Both green and black tea contain relatively high levels of quercetin. A red tea called Rooibos also contains quercetin, although at lower levels than found in other types of tea. Black decaffeinated tea holds the most quercetin, followed by green tea and then caffeinated black tea, according to the United States Department of Agriculture. Brewed tea contains more antioxidants than bottled tea. Green tea is especially rich in the antioxidant catechin, another anti-carcinogen. Dry green tea contains roughly three-and-a-half times more catechins than dry black tea, according to the USDA.

Onions

• The body absorbs three times more quercetin from onions than from apples, according to a study from Wageningen Agricultural University in the Netherlands. The study also found that the body absorbs two times more quercetin from onions than from tea. Scientists from the Netherlands and Ireland estimate that one, 100 g onion contains anywhere from 22 mg to 52 mg of quercetin. Onions also contain calcium, and a study from the Swiss University of Bern suggests that eating dried onion may increase bone mineral density, helping people fend off osteoporosis. Onions also contain vitamin C, potassium, fiber, iron and protein.