Researchers from Rush University in the US found that people who ate at least one serving of green, leafy vegetables a day had a slower rate of decline on tests of memory and thinking skills than people who never or rarely ate these vegetables.
The difference between the two groups was the equivalent of being 11 years younger in age, according to study published in the journal Neurology.
"Adding a daily serving of green, leafy vegetables to your diet may be a simple way to foster your brain health," said Martha Clare Morris, of Rush University.
The study involved 960 people with an average age of 81 who did not have dementia and were followed for an average of 4.7 years.
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The participants completed a questionnaire about how often they ate certain foods and had their thinking and memory skills tested yearly during that time.
The questionnaire asked how often and how many servings people ate of three green, leafy vegetables: spinach, kale and lettuce salad.
The people in the top serving group ate an average of about 1.3 servings per day. Those in the lowest serving group ate on average 0.1 servings per day.
Overall, the participants' scores on the thinking and memory tests declined over time at a rate of 0.08 standardised units per year.
Over 10 years of follow-up, the rate of decline for those who ate the most leafy greens was slower by 0.05 standardised units per year than the rate for those who ate the least leafy greens.
The results remained valid after accounting for other factors that could affect brain health such as smoking, high blood pressure, obesity, education level and amount of physical and cognitive activities.