Researchers tracked almost 28,000 men for two decades to examine how their fruit and vegetable consumption affected their brain power.
They found men who drank a small glass of orange juice were 47 per cent less likely to have difficulty remembering, following instructions or navigating familiar areas.
Lapses in memory, understanding and episodes of confusion can be early signs of brain decline which can ultimately lead to life-threatening dementia.
An estimated 46.8million people are living with dementia worldwide – 850,000 within in the UK, and five million in the US.
There is no cure for the condition but scientists have been trying to find a cure for the memory-robbing disorder for years.
This new evidence reiterates the importance of a healthy diet in staving off the degeneration of the brain which comes with old age.
'Fruits and vegetables are rich in vitamins and nutrients, including antioxidants, that can help protect the brain,' said Dr Hannah Gardener, a researcher at the University of Miami, who wasn't involved with the research.
These health-giving benefits can protect the brain from a build-up of unwanted molecules and maintain a healthy blood supply to the brain.
Lead study author Changzheng Yuan said long-term intake of veg, fruit and orange juice 'may be beneficial' for maintaining cognitive function.
Participants in the Harvard University study answered questionnaires about what they ate every four years.
The researchers sorted the men - aged 51 on average at the start of the study - into five groups based on their intake of fruit and veg.
The group with the highest consumption ate about six servings of vegetables a day, compared to two servings for the group with the lowest consumption.
A serving of vegetables is considered one cup of raw vegetables or two cups of leafy greens.
For fruits, the top group ate about three servings per day, compared to half a serving in the bottom group.
A serving of fruit is considered one cup of fruit or a half-cup of fruit juice.
To measure how this affected brain health, the researchers took tests of thinking and memory skills when the men were 73 years old, on average.
The tests asked things such as whether the men could remember recent events or items on shopping lists.
Overall, 6.6 percent of men who ate the most veg developed poor cognitive function and performed badly on the tests, compared with 7.9 percent of men who ate the least.
Fruit consumption, overall, didn't appear to influence the risk of moderate cognitive problems.
But drinking orange juice did, according to the research, published in the journal Neurology.
Just 6.9 of people who drank orange juice every day went on to develop poor cognitive function.
In comparison, the figure was 8.4 per cent of men who drank orange juice less than once a month.
'The protective role of regular consumption of fruit juice was mainly observed among the oldest men,' Ms Yuan said.
'Since fruit juice is usually high in calories from concentrated fruit sugars, it's generally best to consume no more than a small glass (four to six ounces) per day.'
The study didn't intend to find the link between a healthy diet and memory, however.
Therefore it lacked data on participants memory skills at the beginning of the study, which would have shown how their diet might have influenced this over time.
Dr Hannah Gardener added: 'Fruit and vegetable consumption may be a piece of the puzzle to maintaining cognitive health and should be viewed in conjunction with other behaviors believed to support cognitive health.'
The Daily Mail
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