An old proverb attests to the health benefits of the fruit: "An apple a day keeps the doctor away." Research suggests that apples may reduce the risk of colon cancer, prostate cancer and lung cancer. Like many fruits, apples contain Vitamin C as well as a host of other antioxidant compounds, which may reduce the risk of cancer by preventing DNA damage. The fibre content, while less than in most other fruits, helps regulate bowel movements and may thus reduce the risk of colon cancer. They may also help with heart disease, weight loss and controlling cholesterol, as they do not have any cholesterol, have fibre (which reduces cholesterol by preventing reabsorption), and are bulky for their caloric content like most fruits and vegetables.
A group of chemicals in apples could protect the brain from the type of damage that triggers such neurodegenerative diseases as Alzheimer's and Parkinsonism. Chang Y. 'Cy' Lee of the Cornell University found that the apple phenolics, which are naturally occurring antioxidants found in fresh apples, can protect nerve cells from neurotoxicity induced by oxidative stress. The researchers used red delicious apples from New York State to provide the extracts to study the effects of phytochemicals. Lee said that all apples are high in the critical phytonutrients and that the amount of phenolic compounds in the apple flesh and in the skin vary from year to year, season to season and from growing region to growing region (November/December 2004 issue of the Journal of Food Science). The predominant phenolic phytochemicals in apples are quercetin, epicatechin, and procyanidin B2 (PMID 14558772).
The seeds are mildly poisonous, containing a small amount of amygdalin, a cyanogenic glycoside, but a large amount would need to be chewed to have any toxic effect.
Pesticide contamination is linked to an increasing number of diseases, and they are mostly found on the outside of fruits and vegetables. Washing or peeling before eating may reduce pesticide intake but peeling will also reduce the intake of the beneficial nutrients.
Apple consumption can help remove trapped food and clean between the teeth, but the malic acid contained within the fruit is also capable of eroding tooth enamel over time, and through excess consumption.