Fruit, Vegetables Have Modest Effect on Chronic Disease Risk

Fruit, Vegetables Have Modest Effect on Chronic Disease Risk

BOSTON--Researchers from the Harvard School of Public Health evaluated the relationship between fruit and vegetable intake, the incidence of cardiovascular disease (CVD) and cancer, and of deaths from other causes in two prospective cohorts.

The study, published in the Nov. 3 issue of the Journal of the National Cancer Institute (96, 21:1577-84, 2004) (http://jncicancerspectrum.oupjournals.org), included 71,910 female participants in the Nurses Health study and 37,725 male participants in the Health Professionals Follow-up Study who were free of major chronic disease and completed baseline semi-quantitative food frequency questionnaires in 1984 and 1986, respectively.

Dietary information was updated in 1986, 1990 and 1994 for women, and in 1990 and 1994 for men. Participants were followed for incidence of CVD, cancer or death through May 1998 (women) and January 1998 (men). Multivariable adjusted relative risks (RR) were calculated with Cox proportional hazards analysis. Relative risks is a measure of how much a particular risk factor influences the risk of a specified outcome. (ex. a RR of 2 means a two-fold increased risk of having a specified outcome, whereas a RR of 0.5 means half the risk of the specified outcome).

For men and women combined, participants in the highest quintile of total fruit and vegetable intake had a RR for major chronic disease of 0.95 times that of those in the lowest. Total fruit and vegetable intake was inversely associated with risk of CVD, but not with overall cancer incidence, with RR for an increment of five servings daily of 0.88 for CVD and 1.00 for cancer.

Of the food groups analyzed, green leafy vegetable intake showed the strongest inverse association with major chronic disease and CVD. For an increment of one serving per day of green leafy vegetables, RRs were 0.95 for major chronic disease and 0.89 for CVD.

The scientists concluded increased fruit and vegetable consumption was associated with a modest--although not statistically significant--reduction in the development of major chronic disease. The benefits appeared to be primarily for CVD and not for cancer.

The study did not go unnoticed. My colleagues and I at AICR have read with great interest the cohort study appearing in the Nov. 3 issue of the Journal of the National Cancer Institute, said Ritva Butrum, Ph.D., vice president of research at the American Institute for Cancer Research (AICR). We feel it is important to note that the authors finding in regard to cancer contradicts the preponderance of scientific evidence published to date. The landmark AICR Expert Panel Report Diet, Nutrition and the Prevention of Cancer: A Global Perspective, examined over 4,500 studies and concluded that evidence linking diets high in fruits and vegetables with lower risk for cancer was convincing. Each specific method used by scientists to study the diet has its own set of well-documented limitations, and cannot by itself offer a comprehensive picture.