Eating three portions of colourful fruit and vegetables each day 'may stave off memory loss in old age' - but even having HALF an apple or grapefruit a day could help, finds study

• Eating certain fruits and vegetables can slash the risk of mental decline 
• Antioxidants flavonoids found in grapefruits improve brain health, experts say
• Benefits were seen even when people started consuming flavonoids in later life

Eating plenty of grapefruits, carrots and peppers can lower your risk of mental decline by over a third, new research suggests.

A study has found people who eat a diet that includes at least half a serving per day of food high in flavonoids may have a lower risk of cognitive decline.

Flavonoids are naturally occurring compounds found in plants and are considered powerful antioxidants, and are present in the likes of strawberries, celery and apples.

Harvard University researchers looked at nearly 50,000 men and women over 20 years. 

Participants completed questionnaires about how often they ate various foods, and were asked questions about their cognitive ability.

Results, published in the journal Neurology, found people who consumed more flavonoids in their diets reported a lower risk of cognitive decline.

Flavones, found in some spices and yellow or orange fruits and vegetables, had the strongest protective qualities and were associated with a 38 per cent reduction in risk of cognitive decline - the equivalent of being three to four years younger in age.

Anthocyanins, found in blueberries, blackberries and cherries, were associated with a 24 per cent reduced risk of cognitive decline.

Dr Walter Willett, the study’s author, said: ‘There is mounting evidence suggesting flavonoids are powerhouses when it comes to preventing your thinking skills from declining as you get older.

‘Our results are exciting because they show that making simple changes to your diet could help prevent cognitive decline.’ 

The paper found just half a serving a day - for example half an apple or two heaped tablespoons of cooked spinach - was enough to help prevent mental decline.

However, the participants who consumed the highest amount of flavonoids had around 600mg in their diets each day - the equivalent of eating around five apples or three servings of strawberries.

Dr Willett said: ‘The people in our study who did the best over time ate an average of at least half a serving per day of foods like orange juice, oranges, peppers, celery, grapefruits, grapefruit juice, apples and pears.

‘While it is possible other phytochemicals are at work here, a colourful diet rich in flavonoids-and specifically flavones and anthocyanins-seems to be a good bet for promoting long-term brain health.

‘And it’s never too late to start, because we saw those protective relationships whether people were consuming the flavonoids in their diet 20 years ago, or if they started incorporating them more recently.’

A previous study revealed eating at least six portions of fruit and vegetables per day can reduce stress levels and make you feel less tense.

Researchers said key nutrients could be a factor in explaining the link as flavonoids can reduce inflammation and oxidative stress, which could improve mental wellbeing.

The benefits of a healthy diet are well known, but only about 28 per cent of people in the UK eat the recommended five portions of fruit and vegetables per day.