A daily bowl of strawberries and blueberries may help slow age-related mental decline, research suggests.
Regular consumption of the fruits can delay cognitive ageing by up to 2.5 years, according to information collected from almost 16,000 women.
Scientists in the US analysed health and lifestyle data from the Nurses' Health Study which recruited almost 122,000 registered nurses aged 30 to 55 in 1976.
Between 1995 and 2001, mental ability was measured in 16,010 of the women who were older than 70.
Those who had consumed larger amounts of strawberries and blueberries appeared to experience slower mental decline.
Strawberries and blueberries are rich in flavonoid chemicals that have powerful antioxidant and anti-inflammatory properties.
Study leader Dr Elizabeth Devore, from Harvard Medical School in Boston, said: "We provide the first epidemiologic evidence that berries may slow progression of cognitive decline in elderly women.
"Our findings have significant public health implications as increasing berry intake is a fairly simple dietary modification to test cognition protection in older adults."
The findings are published in the journal Annals of Neurology.
Despite adjusting for influencing factors, the researchers said they could not rule out the possibility of some effect from other lifestyle choices such as exercise.
Dr Eric Karran, from the charity Alzheimer's Research UK, said: "Population studies like this can provide useful clues about the effects of lifestyle and diet on cognition but we must be sensible when interpreting the results. The study suggests a link between eating berries and slower cognitive decline but there could be many factors at play.
"It is not possible to say whether the increased consumption of berries resulted in an increased, beneficial level of flavonoid antioxidants in the brain. Further research will be needed to conclude whether antioxidants in berries are beneficial in the brain and we can't assume that simply eating berries could protect against cognitive ageing or dementia."
"Understanding the factors that affect our memory and thinking as we age can help us to understand possible risk factors for dementia.
"Previous evidence has shown that eating fruit as part of a healthy diet in mid-life could help to reduce our risk of dementia and so eating a healthy balanced diet is something we should all be thinking about."