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, which were not linked with slowed mental decline in the study. 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 the Rush Institute for Healthy Aging 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.
"This is a sound paper and contributes to our understanding of cognitive decline," said Dr. Meir Stampfer of Harvard's School of Public Health.
"The findings specific for vegetables and not fruit add further credibility that this is not simply a marker of a more healthful lifestyle," said Stampfer, who was not involved in the research.
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; about 60 percent of the study volunteers were black.
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.
Overall, people did gradually worse on these tests over time, but those who ate more than two vegetable servings a day had about 40 percent less mental decline than those who ate few or no vegetables. Their test results resembled what would be expected in people about five years younger, Morris said,
The study also found that people who ate lots of vegetables were more physically active, adding to evidence that "what's good for your heart is good for your brain," said neuroscientist Maria Carillo, director of medical and scientific relations for the Alzheimer's Association.
The study examined mental decline but did not look at whether any of the study volunteers developed Alzheimer's disease.
On the Net:
Alzheimer's Association: http://www.alz.org/brainhealth/overveiw.asp