By  Rishi Sharma, M.D.

Sweet and refreshing, berries are thought of as a summer treat, but new evidence suggests that these fruits eaten regularly may also help preserve brain function.

Harvard researchers  found that women who said they ate more blueberries and strawberries were more likely to display less-rapid cognitive deterioration as they aged.

"Our findings have significant public health implications as increasing berry intake is a fairly simple dietary modification to test cognition protection in older adults,"  lead study author Dr. Elizabeth Devore of Harvard Medical School said in a news release.

In the study, which was partially funded by the California Strawberry Commission and published Thursday in the journal Annals of Neurology, researchers  analyzed data gathered by the Nurses  Health Study in which participants had filled out  questionnaires and described their dietary habits and other aspects of their lives every two to four years since 1980.

Starting in 1995, cognitive, or intellectual,  function was measured in the participants on two separate occasions.  When Devore and her colleagues examined the data, they found that participants who had recorded increased servings of blueberries and strawberries preserved their brain function to a greater degree than those who had not. This remained true even after socioeconomic factors were taken into account. Moreover, the researchers found that those who had the highest berry intake over time  could delay cognitive aging by up to two and a half years.

Why might this be? One theory has to do with the fact that blueberries and strawberries are both high in compounds called anthocyanidins and flavonoids, which have powerful antioxidant properties. The researchers believe that these two substances contribute to a delay in cognitive aging. Flavonoid-rich fruit juices have been found  to improve short- term intellectual  performance in small trials.  Anthocyanidins are a particular subclass of flavonoids, which localize in areas of learning and memory.

But don't run to the grocery store just yet, as the study still leaves some questions.

"This is an association or correlation.  It is not proof of causality," said Dr. Clifford Saper, a professor of neurology at Harvard Medical School.  "Also, we do not know what component of the berries may have caused a better result. So, to say that higher intake of flavonoids appears to reduce rates of cognitive decline is just not valid."

The berry eaters also tended to practice many more other healthy behaviors than the nonberry eaters.

Another shortcoming of  the study is that it looked only at women. The researchers pointed out that there is little evidence to find changes in intellectual functioning related to one's sex.  Nonetheless, experts agree that future studies should also include men.

The new study is not the first to ascribe health benefits to berries. Blueberries, in particular, have been linked to improved cholesterol levels, boosts in immune system function and a delay in age-related medical changes.