15 Aug 2021

How fruit and veg may reduce risk of cognitive decline

From Sunday Morning, 8:18 am on 15 August 2021

Eating colourful fruit and vegetables is not only good for you, it may be crucial for your brain health.

A diet rich in 'flavonoids' - a group of natural substances found in plants - can significantly reduce a person's risk of developing early signs of cognitive decline, according to a new Harvard University study.

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People who eat flavonoid-rich foods over many years have better cognitive function later in life, Harvard researcher Tian-Shin Yeh tells Jim Mora.

The study, which was published in the journal Neurology, followed nearly 80,000 middle-aged people for more than 20 years, Dr Yeh says.

It provides another piece of evidence to further the understanding of the role flavonoids play on cognitive health over many years.

“We were able to evaluate the associations between the long-term consumption of these foods and late-life cognitive function.

“What we found was that men and women with higher intake of flavonoid-rich foods over many years had better cognitive function later in life.”

The study showed foods that contain 'flavones' – a subclass of flavonoids – have the strongest association with reduced risk of cognitive decline, Dr Yeh says. These include celery and peppers.

Another subclass of flavonoids called 'flavanones' had the second strongest association with reduced risk - a 36 percent reduction.

Meanwhile, anthocyanins – a natural substance found in fruits coloured red, purple, blue –  are associated with a 24 percent reduction in risk, according to the study. These include purple grapes, blackberries, strawberries, and raspberries.

We also now know it’s never too late to start incorporating more of these plant-based foods into your diet, Dr Yeh says.

Researchers found cognitive function was improved by flavonoids whether they were consumed 20 years ago or more recently.

The best results were seen in people who kept up a consistently high intake of flavonoids over the follow-up period, though, she says.

“We also noticed the association was stronger for younger participants, and we think this may suggest that earlier consumption of flavonoids may be related to additional benefits or the association may be stronger with early onset dementia.”

Although research on flavonoids’ effect on cognitive health has been inconclusive so far, Dr Yeh says this study has taken into account a lot of lifestyle and dietary factors as well as data on non-dietary risk factors on cognitive decline.

“The large sample size and long follow up duration are some of the strengths of this study.

“We also controlled for other dietary factors, including dietary intakes for carotenoids, Vitamin C, D, E, Omega-3 fatty acids, sugar-sweetened beverages, whole grain, fine grain and animal fat.

“Our findings should be independent of these factors.”

Dr Yeh now hopes to see a larger randomised trial involving thousands of people across many years to be able to show a more definitive link between flavonoids and cognitive health.

“There are some short-term randomised control trials suggesting that flavonoids supplements may be beneficial for cognitive performance, but future studies, perhaps with longer study durations and larger sample sizes are needed to confirm the findings.

“In the meantime, the consumption of flavonoid-rich foods seems to be the best choice in part because components other than flavonoids in these foods may be providing some of the benefits.”

While flavonoids, in particular, appear to be important for brain health, Dr Yeh says it's wise to eat a variety of fruits and veggies, not just those that are flavonoid-rich.

“It may take a team effort from all kinds of nutrients and a healthy lifestyle to keep your brain healthy.

“For example, you can make these fruits into smoothies, have a glass of orange juice in the morning or a bunch of berries as snacks, or you can have a banana before or after your workout. Find a way that works best for you so that it would be more practical to keep these foods constantly consumed in your life.

“Importantly, these foods have other health benefits, especially for the cardiovascular system, so there are multiple reasons to be consuming them.”

Dr Tian-Shin Yeh is from the Harvard School of Public Health and part of the Oxford-Harvard joint program in Epidemiology.