People who eat or drink more foods with antioxidant flavonols, found in several fruits and vegetables as well as tea and wine, may have a slower rate of memory decline, according to a study published in the November 22, 2022, online issue of Neurology, the medical journal of the American Academy of Neurology.
The study involved 961 people with an average age of 81 without dementia. They filled out a questionnaire each year on how often they ate certain foods. They also completed annual cognitive and memory tests including recalling lists of words, remembering numbers, and putting them in the correct order. They were also asked about other factors, such as their level of education, how much time they spent doing physical activities, and how long they spent doing mentally engaging activities such as reading and playing games. They were followed for an average of seven years.
The people were divided into five equal groups based on the amount of flavonols they had in their diet. While the average flavonol intake in U.S. adults is about 16 to 20 mg per day, the study population had an average intake of total flavonols of 10 mg per day. The lowest group had an intake of about 5 mg per day, and the highest group consumed an average of 15 mg per day — equivalent to about one cup of dark leafy greens.
To determine rates of cognitive decline, researchers used an overall global cognition score summarizing 19 cognitive tests. The average score ranged from 0.5 for people with no thinking problems to 0.2 for people with mild cognitive impairment to -0.5 for people with Alzheimer’s disease.
After adjusting for other factors that could affect the rate of memory decline, such as age, sex, and smoking, researchers found that the cognitive score of people who had the highest intake of flavonols declined at a rate of 0.4 units per decade more slowly than people whose had the lowest intake. Holland noted this is probably due to the inherent antioxidant and anti-inflammatory properties of flavonols.
“It’s exciting that our study shows making specific diet choices may lead to a slower rate of cognitive decline,” said study author Thomas M. Holland, MD, MS of Rush University Medical Center in Chicago. “Something as simple as eating more fruits and vegetables and drinking more tea is an easy way for people to take an active role in maintaining their brain health.”
Flavonol’s four constituents — kaempferol, quercetin, myricetin, and isorhamnetin — were also considered. The top food contributors for each category were as follows:
- Kaempferol: kale, beans, tea, spinach, and broccoli
- Quercetin: tomatoes, kale, apples, and tea
- Myricetin: tea, wine, kale, oranges, and tomatoes
- Isorhamnetin: pears, olive oil, wine, and tomato sauce
People who had the highest intake of kaempferol had a 0.4 units per decade slower rate of cognitive decline compared to those in the lowest group. Those with the highest intake of quercetin had a 0.2 units per decade slower rate of cognitive decline compared to those in the lowest group. And people with the highest intake of myricetin had a 0.3 units per decade slower rate of cognitive decline compared to those in the lowest group. Dietary isorhamnetin was not tied to global cognition.
Holland noted that the study shows an association between higher amounts of dietary flavonols and slower cognitive decline but does not prove that flavonols directly cause a slower rate of cognitive decline.
Other limitations of the study are that the food frequency questionnaire, although valid, was self-reported, so people may not accurately remember what they eat.
The current study’s findings suggest that dietary intake of total flavonols and several constituents may slow the rate of decline in global cognition and in several cognitive domains including episodic memory, semantic memory, visuospatial ability, perceptual speed, and working memory. There is great value in investigating additional cohorts and groups, to aid in future validation. Further studies are required to confirm the observed associations in other populations and help elucidate and understand the underlying biologic mechanisms involved.