CHICAGO - Eating two or more servings of vegetables a day may slow a person's mental decline by about 40 percent compared with a person who consumes few vegetables, according to a six-year study of nearly 4,000 people age 65 or older.

Consuming lots of fruit did not appear to offer the same mental protection, although fruit has been associated with a wide variety of other health benefits, said Martha Clare Morris, chief of Rush University Medical Center's Rush Center for Healthy Aging.

The slowdown in the rate of cognitive decline experienced by people who ate 2.8 or more servings of vegetables a day is ``equivalent to about five years of younger age'' compared with people who ate less than one vegetable a day, Morris reports in today's issue of Neurology, (www.neurology.org), the scientific journal of the American Academy of Neurology.

The study also suggested it may never be too late to reap the benefits of vegetable consumption. Older people who started eating more than two vegetables a day still showed a significant delay in mental decline, Morris said. One serving of a vegetable is generally equal to a cup.

Rush's third study

The new findings come on top of two previous studies at Rush indicating that the foods people eat may significantly affect their mental agility. Morris reported four years ago that eating foods high in vitamin E appeared to reduce the risk of Alzheimer's disease, and last year she found that eating fish had a similar effect.

Vegetables, especially those in the green leafy category, are brimming with antioxidant compounds such as vitamin E, flavonoids and carotenoids. Vegetables also contain more vitamin E than fruit does, Morris said.

Eating vegetables with olive oil, vegetable oil or some other kind of poly- or mono-unsaturated fats enhances the body's absorption of antioxidants, which help snuff out cell-damaging free radicals, she said.

In trying to figure out which specific food groups bestow important health benefits, epidemiologists match people as closely as possible so other factors in their lifestyles cancel out.

``When we controlled for all of those healthy lifestyle variables -- physical exercise, age, sex, race, education, cognitive activity, participation -- the effects of vegetables on cognition actually became stronger,'' Morris said.

What about fruit?

Matt Kaeberlein, who conducts research on the biochemical processes of aging at the University of Washington, said he was surprised the study did not show any beneficial effect of eating fruit on cognitive decline.

Studies in animals, he said, show that berries -- particularly blueberries, strawberries and cranberries -- seem to protect memory in aging animals. A diet high in fruits and vegetables has been linked to protection against heart disease, cancer, stroke, diverticulosis, diabetes and obesity.

Morris agreed that animal research indicates that berries might help preserve memory but that too few people in the study consumed berries regularly to determine whether they helped preserve memory and other cognitive functions.

``The link between better cognition and vegetables is interesting and certainly real,'' Kaeberlein said. ``But I wouldn't change my diet to stop eating fruits based on this study. There's plenty of evidence that for overall health you're going to be better off eating a diet that's high in both fruits and vegetables.''

Further research is needed to document the exact role that vegetables play in mental health, Kaeberlein said. Learning which specific nutrients provide the greatest protection could lead to developing a pill people could take that would have the same benefits, he said.