So-called “green” diets rich in plant foods are all the rage — and that’s a good thing for people’s health prospects.

Diets rich in plant foods clearly reduce the risks of heart disease, dementia, and cancer, among other threats — and ones also rich in seafood look even better.

The benefits of fruits, vegetables, beans, nuts, seeds, herbs, spices and whole grains flow from their abundant fiber, vitamins, and minerals, and — and last but far from least — antioxidants.

Likewise, coffee, raw cocoa, tea, and extra-virgin olive oil are rich in antioxidants linked to better health outcomes.

Evidence that food-source antioxidants help protect our brains from dementia and other dysfunctions keeps accumulating. For example, see Antioxidant Foods Appear to Keep the Doc Away, and the related articles listed at the end of this one.

Conversely, the so-called “standard American diet” — which is low in fruits, vegetables, and other antioxidant-rich plant foods — is linked to a higher risk for dementia: see Fast Food Diet May Raise Alzheimer's Risk.

Now, a study from Chicago’s Rush University adds yet more evidence that plant-based diets can help reduce the risk or delay the onset of Alzheimer’s and other forms of dementia.

U.S study links antioxidants in plant foods to reduced dementia risk
The new study comes from Chicago’s Rush University, which has produced key research on links between diet and brain health.

In brief, the results showed that the study participants who reported eating or drinking more foods high in antioxidants called flavonols were less likely to develop Alzheimer’s years later (Holland TM et al. 2020).

The study was an analysis of data collected from 921 seniors — aged 81 years on average — participating in the ongoing Rush Memory and Aging Project or MAP, which recruits volunteer subjects from Chicago-area retirement communities and public housing.

On average, volunteers are followed by MAP study researchers for six years. And every year, the volunteers complete a detailed diet questionnaire that asks how often they ate specific foods.

The MAP volunteers also answered questions about known genetic, demographic, health, and lifestyle risk factors for Alzheimer’s, including their levels of education and physical activity, and how much time they spent on mental activities such as reading and playing games.

Annually, the MAP study participants also took standard tests designed to detect signs that they’d developed Alzheimer’s-type dementia.

Based on their annual diet surveys, the participants were placed into five categories of estimated daily flavonol intake, including highest- and lowest-intake categories:

  • Those with the highest flavonol intakes averaged 15.3 mg daily.
  • Those with the lowest flavonol intakes averaged 5.3mg of flavonols daily.

To put those estimated average intakes in perspective, the average American consumes an estimated 16-20mg of flavonols daily.

Annually, all the participants were given standard tests designed to detect signs that they’d developed Alzheimer’s-type dementia.

The Rush University researchers then compared the participants’ estimated flavonol intakes to their dementia-test results and adjusted the results of that analysis to account for the effects of the Alzheimer’s risk factors revealed in the annual participant surveys.

Encouragingly, the results of the researchers’ analysis showed that — compared with the people in the lowest-flavonol-intake group — the people in the highest-flavonol-intake group were 48% less likely to develop Alzheimer’s dementia.

Put another way, only 15% of those in the highest-intake group developed Alzheimer’s dementia, compared with 30% in the lowest-intake group.

“More research is needed to confirm these results, but these are promising findings,” said study co-author Thomas M. Holland, MD.

As he said, “Eating more fruits and vegetables and drinking more tea could be a fairly inexpensive and easy way for people to help stave off Alzheimer’s dementia. With the elderly population increasing worldwide, any decrease in the number of people with this devastating disease, or even delaying it for a few years, could have an enormous benefit on public health.”

This was an observational study, which — unlike a controlled clinical trial — can’t prove a cause-effect relationship between dietary antioxidants and dementia-deterrence.

In addition, the reliability and universality of this study’s results were limited by two other factors: people may not accurately remember what they eat, and most of the participants were white.

However, its results echo those of many prior observational studies, and fit with two proven points:

  • Dementia is promoted by a body’s failure to fully control oxidation and inflammation.
  • Flavonols display fairly potent antioxidant and anti-inflammatory powers in laboratory and clinical studies.

The MAP study — and this Rush University team’s analysis of its data — were supported by the National Institutes of Health, National Institute on Aging and US Department of Agricultural Research Service.

Which flavonols (and foods) delivered the biggest risk reduction?
Using the participants answers to the diet surveys, the Chicago categorized people’s intakes of the four most common types of flavonols, and identify the top food sources:

  • Isorhamnetin – pears, extra-virgin olive oil*, wine, and tomato sauce
  • Kaempferol – kale, beans, tea, spinach, and broccoli
  • Myricetin – tea, wine, kale, oranges, and tomatoes
  • Quercetin – tomatoes, kale, apples, and tea

*Only extra-virgin grade olive oil abounds in flavonols (and other antioxidants). Regular olive oil is cheaper and may have been preferred among the study's limited-income participants, but has almost no antioxidants.

Based on the participants' answers to the annual diet surveys, the researchers calculated the estimated Alzheimer’s risk-reduction associated with higher estimated intakes of each different flavonol:

  • Isorhamnetin-rich diets – 38% less likely to develop Alzheimer’s.
  • Kaempferol-rich diets – 51% less likely to develop Alzheimer’s.
  • Myricetin-rich diets – 38% less likely to develop Alzheimer’s.
  • Quercetin-rich diets – no reduction in Alzheimer’s risk.

The study was supported by the National Institutes of Health, National Institute on Aging and US Department of Agricultural Research Service.

Why would flavonols help prevent or delay dementia?
Flavonols belong to the larger flavonoid family of polyphenol-type antioxidants, which are found in many plant foods and exert beneficial health effects.

The benefits of flavonols, other flavonoids, and other plant-source antioxidants — such as carotenoids — stem mostly from their so-called nutrigenomic effects on our “working” genes.

Those indirect, nutrigenomic effects include tighter control over free oxygen radicals and the inflammation they promote, which reinforce each other and can damage people’s metabolisms as well as their cells and DNA.

For sample of our past coverage of this topic, see Greens vs. Brain Aging, Colorful Greens and Veggies Keep Minds Sharp, Berries' Brain Benefits Affirmed, Expanded, Brain Benefits from Olive Oil?, Cocoa's Brain Anti-Aging Benefits Affirmed and their links to related articles.


  • Agarwal P, Holland TM, Wang Y, Bennett DA, Morris MC. Association of Strawberries and Anthocyanidin Intake with Alzheimer's Dementia Risk. Nutrients. 2019 Dec 14;11(12). pii: E3060. doi: 10.3390/nu11123060.
  • Holland TM, Agarwal P, Wang Y, Leurgans SE, Bennett DA, Booth SL, Morris MC. Dietary flavonols and risk of Alzheimer dementia. Neurology. 2020 Jan 29. pii: 10.1212/WNL.0000000000008981. DOI: [Epub ahead of print]
  • Root M, Ravine E, Harper A. Flavonol Intake and Cognitive Decline in Middle-Aged Adults. J Med Food. 2015 Dec;18(12):1327-32. doi: 10.1089/jmf.2015.0010. Epub 2015 Sep 1.