SPH Researchers Find Fruits, Vegetables Reduce Risk of Stroke

October 07, 1999

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Harvard researchers have found that eating five servings per day of fruits and vegetables is related to a 30 percent lower risk of ischemic stroke in men and women.

Stroke is the third largest cause of death in the United States, ranking behind heart disease and cancer. With 600,000 suffering stroke each year, it is the leading cause of serious, long-term disability in the United States.

Previous studies have indicated that nutritional components found in fruits and vegetables, such as fiber, antioxidants, and potassium, have been associated with reduced risk of cardiovascular disease. However, few good studies examined these foods in relationship to stroke. Until now.

"We found strong evidence of a protective relationship between the consumption of fruits and vegetables and the incidence of stroke in both men and women," said Kaumudi Joshipura, assistant professor in the School of Public Health's Department of Epidemiology. She is lead author of the report, "Fruit and Vegetable Intake in Relation to Risk of Ischemic Stroke," published in the Oct. 6 issue of Journal of the American Medical Association.

"In particular," Joshipura continued, "cruciferous and green leafy vegetables and citrus fruits and juices were found to have the greatest benefit, especially when the intake was at least five servings per day."

The results of the study are based on analysis of questionnaires from participants in both the Nurses' Health Study and the Health Professionals Follow-Up Study. Joshipura and colleagues examined diet and health data from more than 75,000 women and 38,000 men.

Ischemic stroke is the most common type of stroke, caused by a blockage of blood vessels in the brain. Between 70 and 80 percent of strokes are ischemic. Both men and women are at risk of stroke, with women at a slightly higher risk. Risk of stroke increases with age, although nearly 30 percent of stroke victims are under age 65.

The researchers were able to detect a reduced risk in the surveyed population at just three servings of fruits and vegetables per day, when compared with those reporting the lowest levels of consumption. Risk of stroke was further decreased as consumption increased, leveling out at five servings per day. Consumption of fruits and vegetables in excess of five servings per day did not further reduce risk.

The greatest benefits were found from eating cruciferous vegetables, (vegetables in the cabbage family, such as broccoli, bok choy, cauliflower, and brussels sprouts), green leafy vegetables, citrus fruits, and citrus juice. The researchers suggest that the benefits may reflect the concentration of potassium, folate, fiber, and dietary flavenoids found in these foods, a hypothesis based on other studies proposing such value.

"Other studies have offered evidence of the protective value of these components," said Joshipura. "However, the evidence that any single component offers risk-reduction benefits is inconclusive. Therefore, it is best for us – at this point – to consider fruits and vegetables in their entirety.

"Our study provides further support for previous recomm ations that men and women consume at least five servings per day of fruits and vegetables," said Joshipura. "This will reduce their risk of stroke and improve their overall health."

Kaumudi has a joint appointment at School of Public Health and the School of Dental Medicine. Other researchers contributing to this study are affiliated with the School of Public Health, Harvard Medical School, and Brigham and Women’s Hospital.