2 Antioxidants in Leafy Greens, Tea Linked to Slower Memory Decline

2 Antioxidants in Leafy Greens, Tea Linked to Slower Memory Decline

  • Flavonols are a class of antioxidant compounds found in tea, red wine, broccoli, beans, tomatoes, and leeks that possess anti-inflammatory properties.
  • Evidence, mostly from animal studies, suggests that a higher intake of flavonols may protect against Alzheimer’s disease and dementia.
  • A recent longitudinal study found that a higher dietary intake of flavonols was linked to a slower rate of age-related decline in general and specific areas of cognitive function..

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

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

“A healthy diet that contains a variety of fruits and vegetables is essential for maintaining health, especially brain health. It is generally known that the vitamins and minerals present in these foods are important. But now we understand that it is the entire composition of food, including bioactives like flavonols, which make these foods beneficial.
— Dr. Thomas Holland, study author and professor at the Rush Institute for Health Aging

“As our knowledge of cognitive decline and the disease process of Alzheimer’s dementia expands, and we recognize that it is multifactorial, we need to prepare as best we can with multiple science-based tools to help to halt an eye’s progress towards the ultimate goal of prevention,” said Dr Holland Medical News Today.

Flavonoids are a class of compounds produced by plants that possess antioxidant and anti-inflammatory properties. Flavonoids are found in commonly eaten 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 which 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 main subclasses of flavonoids, including flavonols, flavan-3-ols, flavanones, flavones, isoflavones, and anthocyanins.

Additionally, several compounds make up each subclass of flavonoids. For example, 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 is 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 current study included data from 961 participants residing in retirement communities and public housing for the elderly in Chicago and enrolled in the Rush Memory and Aging Project. The Rush Memory and Aging Project is a longitudinal study aimed at identifying factors associated with the decline in cognitive and motor functions caused by aging and Alzheimer’s disease.

Participants were between the ages of 58 and 100 and did not have a diagnosis of dementia at the time of enrolment. Researchers assessed participants to assess cognitive function and risk factors associated with cognitive decline on an annual basis.

To assess cognitive function, a trained technician administered a battery of 19 tests encompassing five different cognitive domains. These five areas 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 that temporarily stores and manipulates information
  • perceptual speed – the ability to quickly process visual information
  • visuospatial ability – ability to perceive spatial relationships and mentally manipulate images

Based on overall performance on 19 cognitive tests, the researchers quantified each participant’s overall cognitive function.

To assess dietary intake of flavonols and individual constituents of flavonols, the researchers used a standardized questionnaire to estimate the frequency of consumption of foods containing flavonols over the past year.

The researchers then examined the association between dietary flavonol intake and cognitive function after adjusting for factors associated with cognitive decline, including age, gender, education level, smoking status, levels of physical activity and participation in cognitively stimulating activities.

Analyzes suggested that higher flavonol intake was associated with a slower decline in overall cognitive function.

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

Additionally, higher intake of the flavonols kaempferol and quercetin, but not isorhamnetin and myricetin, were associated with a slower decline in overall cognitive function.

By examining changes in specific cognitive domains, researchers found that higher flavonol intake was associated with slower declines in episodic memory, semantic memory, perceptual speed, and working memory. , but not visuospatial ability.

Among the individual constituents of flavonols, 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 altered cognitive abilities, but was suggestive for working memory.

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

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

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

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

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

Additionally, Dr. Martin Root, a retired professor from Appalachian State University, who was not involved in the study, noted:

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

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

The study authors acknowledged that their study had some 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 therefore the possibility of ‘residual confounding’ by measured and unmeasured factors – meaning there could be things participants are doing that could help or harm their cognitive abilities/cognitive decline, which we don’t measure or know about,” Dr Holland noted.

Additionally, researchers assessed dietary flavonol intake using self-reports, which are subject to bias.

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

The majority of participants enrolled in the study were also white, highly educated, and confined to a limited geographic region. Therefore, the results of the study may not be generalizable to the entire population.

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

“While these limitations exist, findings supporting long follow-up studies of flavonoid intake and cognitive decline would appear to mitigate this alternative explanation for our findings,” he said.

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