The Many Health Benefits of Apples
by Dr. Don Rose, Writer, Life Alert
It seems that old saying is true after all: "an apple a day keeps the doctor away". You know it by heart, and now it turns out apples can help your heart -- as well as other parts of your body. An article that appeared in the Nutrition Journal in 2004 presented scientific data backing up this homespun maxim. The evidence suggests that a diet high in fruits and vegetables may decrease the risk of chronic diseases, such as cardiovascular disease and cancer. Phytochemicals - including phenolics, flavonoids and carotenoids from fruits and vegetables - may be the key to this reduction in disease risk.
The Nutrition Journal paper focused on one fruit in particular: apples. Apples are a widely consumed, rich source of phytochemicals, and epidemiological studies have linked the consumption of apples with reduced risk of some cancers, cardiovascular disease, asthma, and diabetes. In the lab, apples have been found to have very strong antioxidant activity, inhibit cancer cell proliferation, decrease lipid oxidation, and lower cholesterol. Apples contain a variety of phytochemicals, including quercetin, catechin, phloridzin and chlorogenic acid; all are strong antioxidants.
The purpose of the 2004 paper was to review research literature regarding the health benefits of apples and their phytochemicals, phytochemical bioavailability and antioxidant behavior, and the effects of variety, ripening, storage and processing on apple phytochemicals. This article presents condensed highlights from that paper.
In the United States, cardiovascular disease (CVD) and cancer are ranked as the 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.
High cholesterol and obesity are also 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 CVD, 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. In 1998, obesity, another risk factor for CVD as well as for cancer and diabetes, has been estimated to cost the U.S. over 92 billion dollars per year. Understanding the effects of diet on chronic disease may greatly aid in its prevention, while also helping our economy by redirecting billions of wasted dollars back into productive endeavors.
Fruits and vegetables: evidence for their protective effects
As children, many of us were told to "eat your fruits and vegetables because they’re good for you.” Many also heard the adage "an apple a day keeps the doctor away." Recently, several studies have provided scientific support for both of these simple sayings.
In the early 1990's, researchers examined well over 100 epidemiological studies relating to diet and cancer. In 128 of 156 dietary studies, fruits and vegetables had a significant protective effect against a variety of different cancers. Those consuming low amounts of fruits and vegetables were twice as likely to have cancer compared to those who ate high amounts of these two food groups. Recently, a study linked intake of fruits and vegetables with a reduced risk of breast cancer for women in China. In this population-based, case-control study, pre-menopausal Shanghai 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. 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; 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, such as cataracts, diabetes, Alzheimer’s disease, and even asthma.
Phytochemicals: protective power source for fruits and vegetables
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. 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.
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. We have complex antioxidant defense systems, but they are not perfect and oxidative damage will still occur. Both cardiovascular disease and cancer are thought to be 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.
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 U.S. and in Europe. In the U.S., 22 percent of the phenolics consumed from fruits are from apples, making them the largest source of phenolics. 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. In a Finnish study of approximately 10,000 people, flavonoid intake was associated with a lower total mortality. Apples were one of the main sources of dietary flavonoids that showed the strongest associations with decreased mortality.
Apples are also a good source of antioxidants. When compared to many other commonly consumed fruits in the U.S., apples had the second highest level of antioxidant activity. Apples also ranked second for total concentration of phenolic compounds, and perhaps more importantly, apples had the highest portion of free phenolics when compared to other fruits. This means that these compounds are not bound to other compounds in the fruits, and hence may be more available for eventual absorption into the bloodstream.
Health benefits of apples: an overview
Several studies have specifically linked apple consumption with a reduced risk for cancer, especially lung cancer.
A reduced risk of cardiovascular disease has been associated with apple consumption.
Asthma and pulmonary function
Apple consumption has been inversely linked with asthma (i.e., more apples means less asthma), and it has also been positively associated with general pulmonary health.
Diabetes and weight loss
Not only may apples help decrease the risk of heart disease, cancer, and asthma, but apple consumption may also be associated with a lower risk for diabetes. In the previously discussed Finnish study of 10,000 people, a reduced risk of Type II diabetes was associated with apple consumption.
Apples, and especially apple peels, have been found to have potent antioxidant activity and can greatly inhibit the growth of liver cancer and colon cancer cells.
Apples have been shown to have potent anti-proliferative activity in several studies. When Caco-2 colon cancer cells were treated with apple extracts, cell proliferation was inhibited in a dose-dependent manner. The same trend was seen in Hep G2 liver cancer cells with maximal inhibition reaching 57%. Eberhardt et al. proposed that it is the unique combination of phytochemicals in the apples that are responsible for inhibiting the growth of tumor cells. Apples had the third highest anti-proliferative activity when compared to eleven other commonly consumed fruits.
Inhibition of lipid oxidation
Addition of apple phenolics to human serum decreased DPHPC oxidation in a dose dependent manner. DPHPC is incorporated into low-density lipoprotein (LDL), high-density lipoprotein and very low-density lipoprotein (VLDL) fractions and is an indicator of oxidation. Apple ingestion led to a decrease in DPHPC oxidation, reflecting the apples antioxidant activity in vivo. The protective effects of apples on low-density lipoprotein (LDL) oxidation reached its peak at three hours following apple consumption and returned to baseline levels by 24 hours.
Although apple juice typically contains less phenolics than whole apples, it is still a widely consumed source of dietary antioxidants. Pearson et al examined the effects of six commercial apple juices and Red Delicious apples (whole apples, peels alone, and flesh alone) on human LDL oxidation in vitro. LDL oxidation inhibition varied greatly between brands of fruit juice, ranging from 9 to 34% inhibition and whole apples inhibited LDL oxidation by 34%. Apple peels inhibited LDL oxidation by 34%, while the flesh alone showed significantly less inhibition (21%).
Some of the apple's protective effect against cardiovascular disease may come from its potential cholesterol-lowering ability.
Aprikian et al found that when cholesterol fed rats were supplemented with lyophilized apples, there was a significant drop in plasma cholesterol and liver cholesterols and an increase in high-density lipoproteins (HDL). Furthermore, they found that cholesterol excretion increased in the feces of rats fed apples, suggesting reduced cholesterol absorption.
In a second study, a similar cholesterol lowering effect was seen in cholesterol fed rats when rats were fed apples, pears, and peaches. Apples had a greater cholesterol lowering effect than the other two fruits. The three fruits also increased the plasma antioxidant potential, with apples having the greatest effect. Apples, pears, and peaches all had similar fiber content, but apples contained more phenolic compounds suggesting that perhaps the phenolics in apples contribute to this effect.
In obese Zucker rats, apple consumption lowered cholesterol and low-density lipoproteins (LDL), however in lean rats, apple consumption did not change cholesterol levels.
Aprikian et al found in more recent studies that combined apple pectin and apple phenolic fractions lowered plasma and liver cholesterol, triglycerides, and apparent cholesterol absorption to a much greater extent than apple pectin alone or apple phenolics alone. This suggests there is a beneficial interaction between fruit fiber and polyphenolic components and supports the benefits of eating whole fruits as opposed to dietary supplements.
Based on epidemiological studies, it appears that apples may play a large role in reducing the risk of a wide variety of chronic diseases and maintaining a healthy lifestyle in general. Of the papers reviewed, apples were most consistently associated with reduced risk of cancer, heart disease, asthma, and Type II diabetes when compared to other fruits and vegetables and other sources of flavonoids. Apple consumption was also positively associated with increased lung function and increased weight loss.
Partially because of such strong evidence supporting the health benefits of apples, there is increasing research using animal and in vitro models that attempt to more clearly explain these health benefits. Animal studies and in vitro work are starting to define mechanisms by which apples may help prevent chronic disease. First, the strong antioxidant activity of apples may help prevent lipid and DNA oxidation. Cancer cell culture work has shown that apples inhibit cell proliferation in vitro, which may contribute to the association of apple intake with decreased cancer risk. Apples significantly lowered lipid oxidation both in humans and rats and lowered cholesterol in humans. These effects, which may be attributed to both the phenolics and the dietary fiber found in apples, may partially explain the inverse association of apple intake and risk of cardiovascular disease.
Apple phytochemicals: an overview
Apples contain a large concentration of flavonoids, as well as a variety of other phytochemicals, and the concentration of these phytochemicals may depend on many factors, such as the cultivar of the apple, harvest and storage of the apples, and processing of the apples. The concentration of phytochemicals also varies greatly between the apple peels and the apple flesh.
Because the apple peels contain more antioxidant compounds, especially quercetin, apple peels may have higher antioxidant activity and higher bioactivity than the apple flesh. Research showed that apples without the peels had less antioxidant activity than apples with the peels. Apples with the peels were also better able to inhibit cancer cell proliferation when compared to apples without the peels. More recent work has shown that apple peels contain anywhere from two to six times (depending on the variety) more phenolic compounds than in the flesh, and two to three times more flavonoids in the peels when compared to the flesh. The antioxidant activity of these peels was also much greater, ranging from two to six times greater in the peels when compared to the flesh, depending on the variety of the apple. This work is supported by Leontowicz et al who found that rats consuming apple peels showed greater inhibition of lipid peroxidation and greater plasma antioxidant capacity when compared to rats fed apple flesh.
Many of these phytochemicals from apples have been widely studied, and many potential health benefits have been attributed to these specific phytochemicals. The procyanidins -- epicatechin and catechin -- have strong antioxidant activity and have been found to inhibit low density lipoprotein (LDL) oxidation in vitro. In mice, catechin inhibits intestinal tumor formation and delays tumor onset. Sawa et al. (1999) found that chlorogenic acid has very high alkyl peroxyl radical (ROO•) scavenging activity. Since ROO• may enhance tumor promotion and carcinogenesis, chlorogenic acid may add to the protective effect of apples against cancer.
Quercetin is also a strong antioxidant and is thought to have potential protective effects against both cancer and heart disease. Recently, it has been found that high doses of quercetin inhibit cell proliferation in colon carcinoma cell lines and in mammary adenocarcinoma cell lines. Low levels of quercetin inhibited platelet aggregation; modulation of platelet activity may help prevent cardiovascular disease.
Both animal and cell culture studies show that there is an association between the polyphenolic compounds found within apples and a wide variety of effects that may help prevent chronic disease. This supports the hypothesis that it is the phytochemicals found in fruits, especially apples, that impart healthy benefits. More research is still needed to clarify the effects of these compounds in vivo. In order to examine the effects of these compounds in vivo, it is necessary to understand the bioavailability of the specific compounds, and the bioavailability of these compounds within the fruit matrix.
Health benefits of apples: an overview
Apple phytochemical content is not greatly affected by storage. Quercetin glycosides, phloridzin, and anthocyanin content of Jonagold, Golden Delicious, Red Delicious, Elstar, and Cox's Orange apples were not affected by 52 weeks of storage in controlled atmospheric conditions. After 100 days, the total phenolics in the skin began to decrease, but even after 200 days in storage, total phenolics were similar to those at harvest time.
Apple juice obtained from Jonagold apples by pulping and straight pressing had 10% of the antioxidant activity of fresh apples, while juice obtained after pulp enzyming had only 3% of antioxidant activity. Apple phenolics, especially procyanidins, have been found to bind with cell wall material, which could lead to the decreased levels of polyphenols found in apple juices. In short, processing of apples does affect phytochemical content.
Apple pomace is a major waste product accumulated mainly during apple juice processing. Phloridzin, chlorogenic acid, epicatechin, and quercetin glucosides have all been isolated from apple pomace. These phenolics isolated from apple pomace have been found to have high antioxidant activity, suggesting that apple pomace may have dietary health benefits and commercial use.
Millions of pounds of waste applepeels are generated in the production of applesauce and canned apples in New York State each year. Since apple peels contain a majority of the antioxidants compared to the flesh, apple peels have potential as a value-added ingredient in food products. When apple peels were blanched and dried under a variety of conditions (oven-dried at a range of temperatures from 40° to 80°, air-dried, or freeze-dried), the freeze-dried samples had the greatest total phenolic and flavonoid content, and the total phenolic and flavonoid content was actually greater than in fresh peels. Apple peel powder had strong antioxidant activity and greatly inhibited cancer cell proliferation.
Since fruits and vegetables are high in antioxidants, a diet rich in these foods should help prevent oxidative stress and may help prevent chronic disease, plus slow down aging. Based on these findings,the National Research Council recommends 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.
In numerous epidemiological studies, apples have been associated with a decreased risk of chronic diseases such as cardiovascular disease, cancer, and asthma. In vitro and animal studies have demonstrated that apples have high antioxidant activity, can inhibit cancer cell proliferation, decrease lipid oxidation, and lower cholesterol, potentially explaining their role in reducing the risk of chronic disease.
Apples contain a wide variety of phytochemicals, many of which have been found to have strong antioxidant activity and anticancer activity. The interaction of the many apple phytochemicals warrants more study as researchers attempt to further explain the mechanism behind the apple's ability to reduce the risk of chronic disease.
Many factors affect apples’ phytochemical profile and are important to consider as one attempts to understand and maximize their health benefits. The phytochemical composition of apples varies greatly between different varieties of apples, and there are small changes in phytochemicals during the maturation and ripening of the fruit. In general, storage of apples does not seem to greatly affect apple phytochemicals. However, the processing of apples for juice results in a very significant decrease in phenolics. Processed apple peels retain their phenolic and flavonoid compound activity and thus may be used as a value-added ingredient with potent antioxidant activity.
In short, apples exhibit many potential health benefits. Regular consumption of fruits and vegetables, especially apples, as part of a healthy diet seems to aid in the prevention of chronic disease and maintenance of good health. They really may keep the doctor away!
While apples and other fruits do help our health, even healthy folks face everyday risks, especially as we grow older. For example, seniors are more likely than younger adults to suffer a fall. To ensure one is protected against emergencies while at home, a medical alert system
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“Apple phytochemicals and their health benefits” by Jeanelle Boyer and Rui Hai Liu. Article website: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=442131.
The information provided above is, to the best of our knowledge, reliable and accurate. However, while Life Alert always strives to provide true, precise and consistent information, we cannot guarantee 100 percent accuracy; in addition, statements contained within our articles should not be taken as medical advice. Readers are encouraged to research any statements made, use any resource links provided, and/or consult with professionals in the health and medical fields (or other areas) in order to gather more information before drawing conclusions and making decisions.
Dr. Don Rose writes books, papers and articles on computers, the Internet, AI, science and technology, and issues related to seniors.
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