04/09/2013 12:34 EDT | Updated 06/09/2013 05:12 EDT

The Anti-Cancer Properties of Onions

Pity the poor Vidalia. She's southern and mellow, which you might find charming in a mate, but when it comes to onions and their anti-cancer and other health properties, the harsh northern types are far superior.

The pungent, stinky, tear-inducing qualities come from a host of sulfur compounds in the onions,

explained Dr. Irwin Goldman, a researcher and prof at the University of Wisconsin who's wild about onions and agriculture and their relation to human health.And the sulfur compounds are extremely healthy -- harbouring the potential to lower your blood sugar, blood pressure and cholesterol, to thin your blood, to bolster your immune system and to fight cancer directly by helping your liver detox carcinogens.

Vidalias are sweet because they're grown in the low sulfur soils of Georgia, USA.

Onions grown in high sulfur soils are the most potent, Goldman said in a phone interview, and

and long-storage onions -- the red and yellow ones grown all over the world above the 40 degree latitude -- are highest in sulfur.

Onions also contain flavonoids, pigments that produce colour and act as antioxidants, protecting your DNA from damage.

And again, the dark yellow and red varieties come out on top -- containing more flavonoids and exhibiting more antioxidant activity than sweet southern Vidalias and pure white onions. In fact, shallots -- the small onions with yellow skins -- actually rank highest.

One of those flavonoids, quercetin, has been identified as inhibiting the body's production of VEGF (vascular endothelial growth factor), a protein produced by cells that stimulates the growth of blood vessels and thus promotes the growth and spread of tumors.

Quercetin is higher in yellow and red onions than in white ones, and concentrates in the outer layers, including the skin. That means select the smaller onions, peel them gently -- and throw the precious skins into your next soup stock, or at least your compost pile.

Onions require some advance prep: Cut them and then let them sit for about a half an hour, Goldman advised. That will allow the enzymes in the onions to get to work and develop the full complement of sulfur compounds -- at least 50 of them, it seems

And while you're waiting, might it be useful to stick around and snort some of those sulfur fumes? Funny you should ask, suggested Goldman. He's been hoping to study people working at onion ring processing plants, who cry every day. Might they be inhaling some anti-cancer and other health benefits from sulfur in the air? If only he could get the funding...

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