NEW YORK (Reuters Health) - An apple a day may indeed keep the doctor away, new findings from Finland suggest.

In a study of more than 10,000 men and women, individuals who consumed more of plant compounds called flavonoids--especially one type that is most abundant in apples--were less likely to die from heart disease or develop a variety of chronic diseases, including lung cancer, asthma, stroke and diabetes.

"The message of our study is that individuals consuming fruits and vegetables rich in different flavonoids have a reduced risk of overall mortality and of several chronic diseases," Dr. Paul Knekt of the National Public Health Institute in Helsinki told Reuters Health.

Compared to other fruits and vegetables, apples "showed the strongest and most consistent effects," Knekt said. He added, "This study underlines the suggestion that a healthy diet should include plenty of fruits and vegetables," including apples.

Flavonoids, which are found in a variety of fruits and vegetables as well as in tea and red wine, are thought to boost health in part by combating oxidation, a process in which cell-damaging substances called free radicals accumulate. Oxidative damage can be caused by outside factors, such as cigarette smoking, or by factors on the cellular level. Oxidation is suspected of increasing the risk of heart disease, stroke and several other diseases.

Some studies have shown that the risk of cardiovascular disease and cancer decline as consumption of flavonoids rises, but other studies have failed to show a protective effect of the plant compounds.

In the current study, participants filled out a questionnaire and completed an interview to find out what they had eaten during the previous year. Based on average flavonoid contents of foods available in Finland, the researchers estimated each person's flavonoid intake. Through national prescription and disease registries, the researchers tracked the development of disease in the participants for up to 28 years after the initial interview.

The results of the study suggest that the risk of several chronic diseases--including heart disease, stroke, lung and prostate cancer, type 2 diabetes and asthma--drops as the consumption of flavonoids rises, Knekt and his colleagues conclude in a report in the American Journal of Clinical Nutrition. Most of the benefits seemed to stem from quercetin, a powerful antioxidant that is plentiful in apples, although several other flavonoids seemed to be protective as well.

For instance, greater consumption of apples, which are the main source of quercetin in Finland, and onions, which contain a flavonoid called kaempferol, were both linked to a reduced risk of dying from heart disease.

Likewise, the risk of stroke was 30% lower in people who ate the most kaempferol than in those who ate the least. And in men, higher levels of quercetin were linked to lower risks of lung cancer and prostate cancer. Eating lots of foods rich in quercetin also seemed to provide some protection against type 2 diabetes, although the risk reduction was small enough that it could have resulted from chance.

Although the researchers suspect that the antioxidant properties of flavonoids account for some of the benefits of the compounds, they call for additional research in other groups of people who consume different varieties of flavonoid-rich foods. They suggest that such studies, which should take into account factors that might influence the connection between flavonoids and good health--such as lifestyle--may help draw conclusions about the antioxidant compounds.

SOURCE: American Journal of Clinical Nutrition 2002;76:560-568.

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