Young and middle-aged women who ate three or more servings of these fruits per week were found to reduce their risk of heart attack by as much as one-third.

Blueberries and strawberries contain high levels of naturally occurring compounds called dietary flavonoids, also found in grapes and wine, blackberries, eggplant, and other fruits and vegetables. A specific sub-class of flavonoids, called anthocyanins, may help dilate arteries, counter the buildup of plaque and provide other cardiovascular benefits, according to the study.

"Blueberries and strawberries can easily be incorporated into what women eat every week," says Eric Rimm, senior author and professor at Harvard School of Public Health in Boston. "This simple dietary change could have a significant impact on prevention efforts."

Harvard researchers joined with scientists from the U.K.'s University of East Anglia to conduct a prospective study among 93,600 women ages 25-42 registered with the Nurses' Health Study II. The women completed questionnaires about their diet every four years for 18 years.

A separate study also found that women who eat plenty of blueberries and strawberries experience slower mental decline with age than women who consume fewer of the flavonoid-rich fruits. That study was published last year in the Annals of Neurology.