Researchers followed 921 people without dementia for about six years, starting when they 81 years old, on average. During the study, 220 people were diagnosed with probable Alzheimer's disease.
People who had the most flavonols in their diet were about half as likely to develop Alzheimer's than those who consumed the least, the study found.
"Eat your fruits and vegetables, particularly dark leafy greens, and drink some tea every now and again," said lead study author Dr. Thomas Holland of Rush University in Chicago.
"A healthy diet that contains various fruits and vegetables is critical for continued health, especially brain health," Holland said by email.
Flavonols are a type of flavonoid, phytochemicals found in plant pigments that are known to have antioxidant and anti-inflammatory properties, researchers write in Neurology. While some previous research has linked flavonoids in general to a lower risk of Alzheimer's disease, less is known about the impact of flavonols specifically.
For the current study, researchers asked participants to complete annual questionnaires detailing how often they ate certain foods. They also did cognitive tests and other assessments each year to determine if participants had developed Alzheimer's disease.
The study team used the dietary information to tally each person's total average consumption of four flavonols in particular: kaempferol, which is found in kale, beans, tea, spinach and broccoli; quercetin, in tomatoes, kale, apples and tea; myricetin, also in tea, as well as wine, kale, oranges and tomatoes; and isorhamnetin, in pears, olive oil, wine and tomato sauce.
People in the study who had the lowest total amount of flavonols in their diets consumed an average of about 5.3 milligrams a day, compared with 15.3 milligrams for people with the highest flavonol consumption.
While 15% of people who ate the most flavonol developed Alzheimer's disease, this rose to 54% among those who consumed the least. This difference remained even after researchers accounted for other risk factors for Alzheimer's like diabetes, a prior heart attack or stroke, or high blood pressure.
Overall, people with the highest flavonol consumption were 48% less likely than those with the lowest to develop Alzheimer's disease during the study period.
In addition, when researchers looked at the four different types of flavonols, they found that the highest intakes of either isorhamnetin or myricetin were tied to 38% lower odds of developing Alzheimer's, while the highest consumption of kaempferol was tied to a 51% lower risk. Quercetin intake, however, didn't appear tied to Alzheimer's risk.
The study wasn't designed to prove whether or how different foods might impact the development of Alzheimer's disease.
Still, the results add to evidence suggesting that flavonols might be one way people can try to minimize their risk, said Dr. Glen Finney, director of the Geisinger Memory and Cognition Program in Wilkes Barre, Pennsylvania.
"Eating a healthy and diverse diet along with good socialization, physical exercise and keeping mentally active are important for brain health and can make a difference," Finney, who wasn't involved in the study, said by email.
"Keeping normal blood sugar levels and blood pressure on the low end of normal range are also important for brain health," Finney added. "While dementia is an increasing risk as we age, it isn't inevitable and there are things people can do to reduce their risk."
SOURCE: https://bit.ly/2GBkScJ Neurology, online January 29, 2020.