In the United States, as well as in most industrialized countries, cardiovascular disease and cancer are ranked as the top two leading causes of death. The causes of both diseases have been linked to lifestyle choices, and one of the most important is diet. It has been estimated that a healthy diet could prevent approximately 30% of all cancers [1,2]. High cholesterol and obesity are greatly influenced by diet and lifestyle and are costing the United States billions of dollars in health related expenses. High cholesterol, a risk factor for cardiovascular disease, is commonly treated with statin drugs, and it has been estimated that the United States will spend 30 billion dollars per year on cholesterol treatment by statin drugs [3]. In 1998, obesity, a risk factor for cardiovascular disease, cancer, and diabetes, has been estimated to cost the United States over 92 billion dollars per year [4]. Understanding the effects of diet on chronic disease may greatly aid in the prevention of chronic disease.As children, many of us were told to "eat your vegetables because they are good for you", and the adage "an apple a day keeps the doctor away" is still quite popular. Recently, many studies have provided the scientific backing for both of these very common phrases. In the early 1990's, researchers examined well over one hundred epidemiological studies relating to diet and cancer, and in 128 of 156 dietary studies, fruits and vegetables had a significant protective effect against a variety of different cancers [5]. They found that those who consumed low amounts of fruits and vegetables were twice as likely to have cancer compared to those who ate high amounts of fruits and vegetables. Recently, a study linked intake of fruits and vegetables with a reduced risk in breast cancer in woman in China [6]. In this population based, case-control study of women in Shanghai, pre-menopausal women who ate more dark yellow-orange vegetables and more citrus fruits tended to have lower breast cancer risk. Fruit and vegetable intake also appears to have a protective effect against coronary heart disease [7]. Approximately 84,000 women were followed for 14 years and 42,000 men were followed for 8 years. They found that people who ate the highest amount of fruits and vegetables had a 20% lower risk for coronary heart disease, and the lowest risks were seen in people who consumed more green leafy vegetables, and fruits rich in vitamin C. Not only may a diet high in fruits and vegetables help prevent heart disease and cancer, but it may also help protect against a variety of other illnesses. For example, a diet high in fruits and vegetables may help protect against cataracts, diabetes, Alzheimer disease, and even asthma [8-10].Much of the protective effect of fruits and vegetables has been attributed to phytochemicals, which are the non-nutrient plant compounds such as the carotenoids, flavonoids, isoflavonoids, and phenolic acids. Thousands of phytochemicals have been identified in foods, yet there are still many that have not been identified. Different phytochemicals have been found to possess a range of activities, which may help in protecting against chronic disease. For example, phytochemicals may inhibit cancer cell proliferation, regulate inflammatory and immune response, and protect against lipid oxidation [11,12]. A major role of the phytochemicals is protection against oxidation. We live in a highly oxidative environment, and many processes involved in metabolism may result in the production of more oxidants. Humans, and all animals, have complex antioxidant defense systems, but they are not perfect and oxidative damage will occur. Both cardiovascular disease and cancer are thought to be particularly the results of oxidative stress, which can lead to damage of the larger biomolecules, such as DNA, lipids, and proteins. It has been estimated that there are 10,000 oxidative hits to DNA per cell per day in humans [10].A major class of phytochemicals found commonly in fruits and vegetables are the flavonoids. Apples are a very significant source of flavonoids in people's diet in the US and in Europe. In the United States, twenty-two percent of the phenolics consumed from fruits are from apples making them the largest source of phenolics [13]. In Finland, apples and onions are main sources of dietary flavonoids, while in the Netherlands apples rank third behind tea and onions as top sources of flavonoids [14,15]. In a Finnish study of approximately 10,000 people, flavonoid intake was associated with a lower total mortality [16]. Apples were one of the main sources of dietary flavonoids that showed the strongest associations with decreased mortality.Not only are apples commonly enjoyed by many cultures, but they are also a good source of antioxidants. When compared to many other commonly consumed fruits in the United States, apples had the second highest level of antioxidant activity (Figure 1). Apples also ranked the second for total concentration of phenolic compounds, and perhaps more importantly, apples had the highest portion of free phenolics when compared to other fruits [17]. This means that these compounds are not bound to other compounds in the fruits, and the phenolics may be more available for eventual absorption into the bloodstream.

Since fruits and vegetables are high in antioxidants, a diet high in these foods should help prevent oxidative stress, and may therefore help prevent chronic disease and slow aging. These findings have lead to the National Research Council to recommend consuming five or more servings of fruits and vegetables a day. Several commonly consumed foods and beverages, including tea, wine, onions, cocoa, cranberries, and apples, have been targeted as particularly beneficial in the diet because of their high content of phenolic compounds. While active research into the health benefits of these foods has been ongoing, current reviews of this work exist for all of the above-mentioned foods except apples. Therefore, the purpose of this paper is to review the recent literature addressing the health benefits of apples, their phytochemical profile, bioavailability of apple phytochemicals, and factors that may affect the phytochemical quality, such as apple variety, ripening, storage, and processing.