It certainly would be great to spend your money on apples rather than health insurance. Unfortunately, an apple a day will not keep you totally disease free, but there is some evidence that it can help.
Scientists have done many studies looking for a specific chemical in apples that could prove this old adage. Quercetin, a polyphenolic compound (polyphenols are the antioxidant compounds found in red wine), is the compound most referenced for its curative properties. Quercetin was found to help in lung and prostate cancer and to reduce the incidence of cardiovascular disease. Apples also contain other antioxidant compounds and fiber. The peel has the highest proportion of these antioxidants (almost five times greater), so definitely don't skip the peel. There has also been some research that has found that apples help in fighting Alzheimer's and breast cancer.
Researchers in Canada looked at eight varieties of apples and found that Red Delicious and Northern Spy apples had the highest levels of antioxidant chemicals. This study left out many varieties that are also popular in the United States, so your favorite may still be good for you.
It is no magic bullet, but hey, it makes apple pie sound more nutritious, right?