(CNN)Eating a plate full of colorful foods like strawberries and peppers, which include flavonoids, could slow your cognitive decline, a new study found.
People who ate about 600 milligrams (0.02 ounces) of flavonoids per day had a 20% lower risk of cognitive decline than those who ate only 150 milligrams (0.005 ounces) per day, according to the study published Wednesday in the American Academy of Neurology journal.
A 100-gram (3.5-ounce) serving of strawberries has about 180 milligrams (0.006 ounces) of flavonoids, while an apple has about 113 milligrams (0.003 ounces), the study said.
Flavonoids are a series of compounds with strong antioxidant abilities that are commonly found in many fruits and vegetables, said study author Dr. Walter Willett, professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health and professor of medicine at Harvard University in Cambridge, Massachusetts.
Damage to the "blood supply to the brain is an important contributor to cognitive decline," said Willett, adding that the anti-inflammatory properties of flavonoids help protect that blood supply, which in turn slows down the cognitive decline.
Cognitive decline can lead to diseases like dementia and Alzheimer's, he added.
The study spanned nearly a quarter of a century and had about 75,000 participants. The average age of the participants at the start of the study was 50, and they are now in their 70s and 80s, Willett said.
People's brain functions begin to decline in our 20s and 30s, but we usually don't notice it until we reach our 70s, he said. Eating foods high in flavonoids could make the downward slope less steep, he added.
After tracking the participants' diets over 20 years, researchers had them answer a questionnaire multiple times over a four-year period to determine cognitive decline, Willett said.
Each person's cognitive decline was calculated with six yes or no questions. Questions included "Do you have more trouble than usual remembering a short list of items, such as a shopping list?" and "Do you have trouble remembering things from one second to the next?"
Because the study took place over decades, the results are much more valid than other studies that occur over a couple years, said Dr. Daniel Potts, a fellow of the American Academy of Neurology and attending neurologist at the US Department of Veterans Affairs in Tuscaloosa, Alabama, who was not involved in the study.
"Cognitive decline is something that takes place slowly, so when you're assessing it, you're able to pick up subtle changes better over a long period of time," he said.
How to eat more flavonoids
Willett said there isn't a specific number of flavonoids people should eat each day, and they shouldn't be counted or measured.