Having badmouthed apples just a few months ago I now keep running across reasons to eat more of them. I mistakenly said that I didn't know if the saying, 'an apple a day kept the doctor away' had any validity.
It was only a matter of days before I read that apples are an excellent source of glucaric acid, a chemical which encourages detoxification of carcinogens and potentially decreases cancer risk. Now I've stumbled into another piece about apples.
A Finnish study several years ago looked at the relationship between dietary flavonoids and cancer risk. People who ate the most flavonoids had a 20% decrease in overall cancer risk. If they were smokers, high flavonoid consumption had a greater benefit, decreasing risk by 45%. By far the biggest single food to have an effect were apples. Apples decreased cancer rates by 87%.  The presumed explanation for this effect is that apples contain large amounts of quercetin. This isn't the only study which points to benefits from quercetin. Quercetin is usually thought of for its potent anti-inflammatory, anti allergy, and antioxidant activity but it has a role in preventing and treating cancer. In vitro research shows quercetin has significant activity against a range of cancer cell lines, (including breast, ovarian, stomach, skin, colon, and brain cancers) causing the cells to either differentiate into healthy cells or to self destruct (apoptosis). [2,3,4,5,6,7] It appears that quercetin increases the effectiv eness of other cancer treatments. [8.9] It may protect healthy cells from oxidative damage during treatment.[10,11]
Only a fraction of the quercetin taken orally is absorbed.  Common practice is to take equal amounts of Bromelain with quercetin to enhance its activity probably by increasing absorption. It stands to reason that in situations where absorption isn't necessary, quercetin is already strongly indicated. Such situations are preventing and treating cancers of the stomach, intestine, and colon. As we have a great deal of clinical experience using quercetin for treating internal systemic conditions such as rheumatoid arthritis and allergies, we have good reason to believe that it is absorbed and does act in the body in a manner predicted by in vitro research. Aside from apples the best dietary source of quercetin appears to be onions.
Slice the onions into 1/8 inch rings and cook slowly in the oil until lightly browned. add stock and boil for a couple of minutes. Season to taste. Pour Soup into cups or plates, float the toast and cover with a generous helping of cheese. Broil just long enough to brown the cheese and serve.