People who have a diet rich in flavanols, which are found in tea, apples and berries, may be less likely to develop age-related memory loss, research suggests.

A three-year study of 3,562 people aged about 71 found those with high regular flavanol consumption had better hippocampal memory function, which includes short-term memory-making, than those who didn’t.

The research, published in the US journal the Proceedings of the National Academy of Sciences, suggested consuming a supplement of 500mg of flavanols daily could reverse the negative effect on memory function of low flavanol intake in older people.

However, the researchers stressed that flavanol supplements have no effect on people who do not have a flavanol deficiency. Most older adults in the UK already consume high amounts of flavanols through tea, apples and berries.

Lead scientist Scott Small, professor of neurology at Columbia University, said the findings formed part of a growing body of research that is “starting to reveal that different nutrients are needed to fortify our ageing minds”.

The scientists randomly assigned healthy adults to receive either a daily 500mg flavanol supplement or a dummy pill for three years. The participants took several memory tests during the study period and filled in surveys that assessed their diet.

The researchers said memory scores improved only slightly for the group taking the flavanol pill, but that within that group there was a subset of people who had poor diet and low flavanol consumption at the beginning of the study, who saw their memory scores increase by an average of 10.5% compared with the placebo, and by 16% compared with the start of the study.

This research, which is funded by food manufacturer Mars, used flavanols extracted from cocoa, though the study authors said that eating chocolate is unlikely to provide sufficient levels of flavanols, as these are destroyed during processing.

Gunter Kuhnle, professor of nutrition and food science at the University of Reading and co-investigator of the study, said the results “suggest that there is an optimum amount of flavanols in the diet”, which is a daily intake of about 500mg.

Scientists were divided on whether the study shows that flavanol supplements are a good idea for older people.

Prof Aedin Cassidy, chair in nutrition and preventative medicine at Queen’s University Belfast, said it was a “really important study”, especially since the dose required for brain health improvement was “readily achievable”.

“For example, one mug of tea, six squares of dark chocolate, a couple of servings of berries and apples would together provide about 500mg of flavanols,” he said.

Ian Johnson, emeritus fellow at the Quadram Institute in Norwich, said the “large and rigorously conducted” research added to previous evidence “showing the importance of diet as a factor supporting cognitive health in later life”, though he said further studies were probably needed to explore the benefits of flavanol supplements in depth.

However, David Curtis, honorary professor at the UCL Genetics Institute, said the study showed that “those taking a flavanol supplement for years had about the same memory function as those taking placebo and any differences were well within chance expectation”.

He added: “The study fails to provide evidence that increasing flavanol intake is beneficial and there is no need for anybody to contemplate changing their diet in the light of its findings.”

Carl Hodgetts, senior lecturer in cognitive neuroscience at Royal Holloway, University of London, said research into the relationship between nutrition and the brain could help with the fight against dementia.

He said it was “an interesting study that starts to address such questions” but disagreed with the conclusion that flavanol supplements affect hippocampal function, as MRI scans would be needed to establish this.

Flavanols are found in apples, berries and tea. Photograph: Gareth Fuller/PA