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Antioxidants have many proven health benefits. Guido Mieth/Getty Images
  • Flavonols are a class of antioxidant compounds found in tea, red wine, broccoli, beans, tomatoes, and leeks that possess anti-inflammatory properties.
  • Evidence, predominantly from animal studies, suggests that a higher intake of flavonols may protect against Alzheimer’s and dementia.
  • A recent longitudinal study found that higher dietary intake of flavonols was linked to a slower rate of age-related decline in overall and specific domains of cognitive function.

A recent study published in Neurology shows that a higher intake of flavonols—a class of flavonoids present in fruits, vegetables, tea, and wine—was associated with a slower rate of cognitive decline in older adults.

The study adds to the limited but growing data showing an association between dietary flavonol intake and brain health.

“A healthy diet that contains various fruits and vegetables is critical for continued health, especially brain health. It is generally known that the vitamins and minerals found in these food items are important. But now we are understanding that it’s the entire composition of the food, inclusive of bioactives like flavonols, that render these foods beneficial.”
Dr. Thomas Holland, study author, and professor at the Rush Institute for Health Aging

“As our knowledge of cognitive decline and of the disease process of Alzheimer’s dementia expands, and we recognize that it is multi-factorial, we should prepare ourselves as best we can with multiple, scientifically based tools to help stave off the progression with an eye toward the ultimate goal of prevention,” Dr. Holland told Medical News Today.

Flavonoids are a class of compounds produced by plants that possess antioxidant and anti-inflammatory properties. Flavonoids are present in commonly consumed fruits and vegetables, including berries, cherries, leafy vegetables, tomatoes, onions, apples, citrus fruits, and beans. Beverages such as tea and red wine are also major sources of flavonoids in the diet.

Previous studies have shown that a higher dietary intake of flavonoids is associated with a slower rate of cognitive decline that normally occurs with aging as well as due to Alzheimer’s disease. These effects of flavonoids have been attributed to their ability to reduce oxidative stress, decrease inflammation in the brain, and increase brain plasticity.

There are six major subclasses of flavonoids, including flavonols, flavan-3-ols, flavanones, flavones, isoflavones, and anthocyanins.

Moreover, several compounds constitute each subclass of flavonoids. For instance, examples of flavonols include compounds such as quercetin, kaempferol, isorhamnetin, and myricetin.

Although animal studies suggest a beneficial impact of certain flavonols and their individual constituents on cognition, similar data from human studies are limited.

A recent study used longitudinal data to examine the impact of total dietary flavonol intake on the rate of decline in cognitive function that normally occurs in older adults. The study also assessed the association between specific flavonol compounds and age-related changes in cognitive function.

The present study included data from 961 participants residing in retirement communities and senior public housing in Chicago and enrolled in the Rush Memory and Aging Project. The Rush Memory and Aging Project is a longitudinal study with an aim to identify factors associated with the decline in cognitive and motor function caused by aging and Alzheimer’s disease.

The participants were aged between 58–100 years and did not have a dementia diagnosis at the time of enrollment. The researchers assessed the participants to evaluate cognitive function and risk factors associated with cognitive decline on a yearly basis.

To assess cognitive function, a trained technician administered a battery of 19 tests encompassing five different cognitive domains. These five domains included:

  • episodic memory — a form of long-term memory encompassing memories of events and experiences
  • semantic memory — a form of long-term memory encompassing factual and conceptual knowledge
  • working memory — a form of short-term memory which allows one to temporarily hold and manipulate information
  • perceptual speed — the ability to process visual information rapidly
  • visuospatial ability — capacity to perceive spatial relationships and mentally manipulate images

On the basis of overall performance in the 19 cognitive tests, the researchers quantified the global cognitive function of each participant.

To assess the dietary intake of flavonols and individual flavonol constituents, the researchers used a standardized questionnaire to estimate the frequency of intake of foods containing flavonols in the previous year.

The researchers then examined the association between dietary flavonol intake and cognitive function after adjusting for factors associated with cognitive decline, including age, sex, educational attainment, smoking, physical activity levels, and engagement in cognitively stimulating activities.

The analyses suggested that a higher intake of flavonol was associated with a slower decline in global cognitive function.

“In our study population, those that consumed the highest level of flavonols (an average of 7 servings of dark leafy greens/week) versus the lowest had a 32% decrease in their rate of cognitive decline,” said Dr. Holland.

Moreover, a higher intake of the flavonols kaempferol and quercetin, but not isorhamnetin and myricetin, was associated with a slower decline in global cognitive function.

Examining the changes in specific cognitive domains, the researchers found that higher consumption of flavonols was associated with a slower decline in episodic memory, semantic memory, perceptual speed, and working memory, but not visuospatial ability.

Among the individual flavonol constituents, a higher intake of kaempferol was associated with a slower rate of decline in all five cognitive domains. In contrast, myricetin was not associated with a change in any cognitive abilities but was suggestive for working memory.

Quercetin intake was associated with a more gradual decline in episodic memory and semantic memory, whereas isorhamnetin intake was correlated with a more gradual decline in episodic memory and suggestive for visuospatial memory.

Leafy vegetables are the richest source of kaempferol. Tea, onions, leek, broccoli, beans, tomatoes, and berries are some of the other major sources of the other flavanols.

Dr. Holland noted that this study highlights the importance of the consumption of a healthy diet rich in flavonoids.

In addition to having beneficial effects on brain health, another recent study reported an association between a higher intake of flavonoids, including flavonols, and a marker of subclinical atherosclerosis. This further highlights the potential protective effects of flavonoids not just on brain health but also on cardiovascular health.

One of the strengths of the study was the use of a trained technician to objectively evaluate cognitive performance. This is in contrast with subjective assessments used by previous studies examining the association between flavonoids and cognitive function.

In addition, Dr. Martin Root, a retired faculty at Appalachian State University, who was not involved in the study, noted:

“This type of study is difficult to perform due to the difficulty in reliably measuring both dietary intakes and cognitive function. The authors improved on this by repeated measures of both over time and by using 19 measures of cognitive function over 5 domains.”

“Another problem with this type of study is that people who consume a healthy diet also tend to have other healthy habits. Also, foods that contain high flavonols also tend to contain lots of other healthy components like vitamins and minerals. The authors did a respectable job in controlling as best they could for these other complicating factors.”
— Dr. Martin Root

The study’s authors acknowledged that their study had a few limitations. They noted that the study had an observational design; thus, these results do not establish a causal effect of flavonol intake on cognitive decline.

“A limitation of the study is its observational study design, and thus the possibility of ‘residual confounding’ by measured and unmeasured factors—meaning, there could be things the participants are doing that could help or harm their cognitive abilities/cognitive decline, that we are not measuring or privy to,” Dr. Holland noted.

Moreover, the researchers assessed the dietary intake of flavonols using self-reports, which are prone to bias.

Due to their advanced age, the study’s participants may also have experienced a more pronounced cognitive decline due to mild cognitive impairment during the study. These symptoms could make the recall of dietary habits inaccurate or have led to changes in dietary habits.

A majority of participants enrolled in the study were also white, highly educated, and confined to a limited geographic region. As a result, the study’s findings may not be generalizable to the broader population.

However, Dr. Holland noted that these results were consistent with other studies.

“Although these limitations exist, supportive findings from long follow-up studies of flavonoid intake and cognitive decline would appear to lessen this alternative explanation of our findings,” he said.