Researchers in the United States say it is vegetables rather than fruit that protect those over 65 from a decline in cognitive ability.
The researchers from Rush University Medical Center say people who eat at least 3 servings of vegetables a day can slow down their rate of cognitive change by around 40 percent.
The research team led by Martha Clare Morris, ScD, associate professor at Rush University Medical Center in Chicago, Illinois conducted a study into the association between vegetables, fruit and cognitive decline.
The team studied 3,718 residents in Chicago, Illinois, both black and white, who were age 65 and older, over a period of six-years, between 1993-2002.
The participants completed a frequency questionnaire about the foods they ate, including a list of 28 vegetables and 14 fruits, and their vitamin use.
They were given tests of mental skills including memory and attention when the study started, and again three and six years later.
The researchers divided the participants into five groups based on average daily vegetable servings, which ranged from less than one daily serving to four daily servings.
The researchers found that all participants had some mental slowdown as they aged; but when compared to people who consumed less than one serving of vegetables a day, people who ate at least 2.8 servings of vegetables a day saw their rate of cognitive change slow by roughly 40 percent,a decrease equivalent to about 5 years of younger age.
Green leafy vegetables appeared to have the strongest link to slowing the rate of cognitive decline and this was more apparent if the person was older and consumed more than two servings of vegetables a day.
The study rather surprisingly, found fruit consumption was not associated with cognitive change which say the researchers may be due to the high amounts of vitamin E in vegetables which helps to lower the risk of cognitive decline.
Vegetables are also typically consumed with added fats such as salad dressings, and fats increase the absorption of vitamin E.
The vegetables listed in the study included lettuce, tossed salad, spinach, kale, collards, broccoli, cabbage, peas, lima beans, beans, lentils, soybeans (legumes), carrots (cooked or raw), sweet potatoes, zucchini, summer squash, beets and eggplant.
Morris says the study's findings will be useful in simplifying public health messages by saying people should eat more or less of foods in a specific food group, rather than more or less of individual foods.
According to the U.S. Government's Dietary Guidelines (2005) people should eat a variety of fruits and vegetables daily and those who consume 2,000 calories per day should eat two cups of fruit and 2.5 cups of vegetables daily; six baby carrots equates to half a cup as does a small apple.
The study was supported by grants from the National Institute on Aging and is published in the October 24, 2006, issue of Neurology, the scientific journal of the American Academy of Neurology.