Three portions of colourful fruit or vegetables a day could hold the key to staving off memory loss in old age, a major study has found. 

Harvard researchers followed more than 75,000 people in their late 40s and early 50s for 20 years and found those with the most colourful diets were 20 per cent less likely to suffer memory loss. 

The key compounds in brightly coloured foods are a group of chemicals called flavonoids, which are also found in high levels in tea, strawberries, peppers and apples.

Flavonoids have a variety of purposes for plants, including protecting them from stress and UV light, but they have long been known to be highly beneficial for human health. 

The new study, published in the journal Neurology, found that the people who consume the most flavonoids in a day, around 600 milligram, are 19 per cent less likely to suffer cognitive decline in later life compared to people who eat the least, around 150mg a day. 

There are around 180mg of flavonoids in 100 grams of strawberries, and around 113mg in an apple. 

Participants in the study were given regular questionnaires to assess their dietary habits and also their cognitive abilities. 

What food has the most cognitive benefit?

People were asked six questions to gauge the level of cognitive decline, of which memory loss is the primary symptom. 

Two of the questions were: 

  • Do you have more trouble than usual following a group conversation or a plot in a TV programme due to your memory?
  • Do you have trouble finding your way around familiar streets?

Researchers then analysed the data to see what diet components had the most impact on preventing cognitive decline, after taking into consideration other aspects, such as pre-existing health conditions, physical activity and if the person smokes. 

It revealed that eating more flavonoids cut the risk of cognitive decline by a fifth. However, flavonoids is a broad umbrella term, with several subgroups, and these have varying levels of influence. 

For example, flavones, a group of chemicals found in low levels in spices as well as orange and yellow fruits, reduce risk by 38 per cent. 

Peppers are a good source of flavones, and contain just 5mg per 100g serving size. 

Anhocyanins, found in blueberries, blackberries and cherries, were also found to be very good for preventing cognitive decline, with high consumption linked to a 24 per cent reduction in risk. 

Blueberries have about 164mg of anthocyanins per 100g serving.

“Orange juice, oranges, grapefruits, and grapefruit juice were the main food sources of flavanones; while blueberries, strawberries, apples, and red wine were major contributors to anthocyanins,” the researchers wrote.

“The antioxidant properties of flavonoids are one of the many reasons cited for a potential neuroprotective effect.”

“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,” said Dr Walter Willett, the study lead author from Harvard. 

“While it is possible other phytochemicals are at work here, a colorful 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.”