The findings by Rush University Medical Center researchers suggest a diet that includes two to three-and-a-half-cup servings of vegetables might boost the memory and protect against Alzheimer's disease.

    "People who consumed two or more vegetables a day had a 35 to 40 percent decrease in the decline in thinking ability over six years," said study lead author Martha Clare Morris, associate professor at Rush University Medical Center in Chicago. "That's the equivalent of being five years younger in age."

    Morris' team surveyed 3,718 research participants aged 65 or above who live in the south side of Chicago. 

    The researchers used a complete food questionnaire of 139 different food items. They asked about the participants' usual intake and assessed the frequency of intake. During the six-year study, the participants received at least two cognitive tests that measured their memory and thinking speed.  

    "By far, the association with a slower rate of decline was found in the group that ate high amounts of green, leafy vegetables," Morris said. Such foods included lettuce and tossed salad, spinach, kale and collards.

    Eating lots of fruit, this study found, was not associated with benefits similar to eating a vegetable-rich diet. Morris said it's possible that some fruit may contain compounds that counteract antioxidants but further studies are needed to determine whether fruit is brain-protective.

    Other research said fruit did provide similar benefit, so it is still recommended.

    Morris suspected that vegetables may help protect memory and thinking speed because they contain high amounts of vitamin E, an antioxidant that can help reduce the damage caused by free radicals, unstable oxygen molecules generated by normal metabolism that can damage neurons in the brain and contribute to dementia.

    But she said it's too soon to say for sure that vegetables actually preserve the brain from age-related decline.

    "But it's encouraging to see that it appears to slow the rate of decline," she said. "We know that eating vegetables is important for chronic diseases. So this might be one more reason why you should eat your vegetables."

    (Agencies)