Eating five or more servings of fruits and vegetables daily has been recommended to reduce a person's risk of cardiovascular disease and cancer, the leading causes of death in the United States. Studies have evaluated the association of fruit and vegetable consumption with the reduction of risk of specific diseases, but their overall associations with cardiovascular disease and cancer have rarely been evaluated in large cohort studies.
To evaluate the relationship between fruit and vegetable consumption and the incidence of cardiovascular disease and cancer, Walter C. Willett, M.D., of the Harvard School of Public Health in Boston, and colleagues analyzed data from more than 100,000 participants in two large cohort studies, the Nurses' Health Study and the Health Professionals' Follow-up Study.
The researchers found an inverse association between total fruit and vegetable intake and the risk of cardiovascular disease but no relationship with cancer incidence. In an analysis of different groups of fruits and vegetables, consumption of green leafy vegetables showed the strongest inverse association with both cardiovascular disease and major chronic disease--that is, cancer and cardiovascular disease combined.
"Consumption of five or more servings of fruits and vegetables per day has been recommended in the National 5 A Day for Better Health Program for cancer prevention, but the protective effect of fruit and vegetable intake may have been overstated," the authors write. However, "our findings for cardiovascular disease still support the recommendations of the American Heart Association of consuming at least five servings of fruits and vegetables per day."
In an editorial, Arthur Schatzkin, M.D., Dr.P.H., and Victor Kipnis, Ph.D., of the National Cancer Institute, discuss the possibility that substantial errors in measuring diet as well as other confounding factors in the study may have distorted true associations between fruit and vegetable intake and cancer, and they suggest several ways researchers might deal with these problems. They write, "the evidence is simply inadequate at this time to determine whether fruit and vegetable intake confers modest protection against cancer. Researchers should recognize this uncertainty in nutrition and cancer epidemiology and do what it takes to move ahead, especially when it comes to improving exposure assessment in observational studies."
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