On measures of mental sharpness, older people who ate more than two servings of vegetables daily appeared about five years younger at the end of the six-year study than those who ate few or no vegetables.

The research in almost 2,000 Chicago-area men and women doesn't prove that vegetables reduce mental decline, but it adds to mounting evidence pointing in that direction. The findings also echo previous research in women only.

Green leafy vegetables including spinach, kale and collards appeared to be the most beneficial. The researchers said that may be because they contain healthy amounts of vitamin E, an antioxidant that is believed to help fight chemicals produced by the body that can damage cells.

Vegetables generally contain more vitamin E than fruits. Vegetables also are often eaten with healthy fats such as salad oils, which help the body absorb vitamin E and other antioxidants, said lead author Martha Clare Morris, a researcher at Chicago's Rush University Medical Center. 

The fats from healthy oils can help keep cholesterol low and arteries clear, which both contribute to brain health.

The study was published in this week's issue of the journal Neurology and funded with grants from the National Institute on Aging.

The research involved 1,946 people aged 65 and older who filled out questionnaires about their eating habits. A vegetable serving equaled about a half-cup chopped or one cup if the vegetable was a raw leafy green like spinach. They also had mental function tests three times over about six years.

 The tests included measures of short-term and delayed memory, which asked these older people to recall elements of a story that had just been read to them. The participants also were given a flashcard-like exercise using symbols and numbers.