Older adults who regularly consume a group of antioxidants called flavonols may have a decreased risk of developing Alzheimer's disease, a new study suggests.
The compounds exist in many fruits and vegetables, with the richest sources including green vegetables like kale, spinach and broccoli, apples and tea.
The researchers found that of over 900 older adults they followed for six years, the one-fifth with the highest flavonol intake were 48% less likely to develop Alzheimer's than the one-fifth with the lowest intake.
The findings do not prove the antioxidants are a magic bullet against dementia, the researchers stressed. But they add to evidence that a healthy diet -- including plenty of fruits and vegetables -- may help protect the aging brain.
While studies have linked healthy eating habits to a lower risk of mental decline, the new findings get closer to one potential reason, according to lead researcher Dr. Thomas Holland.
"We've understood that fruits and vegetables are great for our health. We wanted to focus more on the 'why,'" said Holland, of Rush University in Chicago.
Flavonols are known to act as antioxidants and fight inflammation, and animal research has suggested particular brain benefits: In lab mice engineered to have a "model" of Alzheimer's, flavonols can curb the buildup of abnormal protein deposits in the brain, and improve memory and learning abilities.
In past research, the Rush team has found that an eating pattern they dubbed the "MIND diet" is related to a lower risk of memory decline and Alzheimer's in older adults.
They describe the diet as a hybrid of the traditional Mediterranean diet and the DASH diet (Dietary Approaches to Stop Hypertension) -- both of which can lower the risks of heart disease and stroke.
The MIND diet emphasizes fruits and vegetables -- leafy greens and berries, in particular -- as well as fiber-rich grains, nuts, beans, olive oil, fish and poultry. It discourages red meat, butter, sweets and highly processed foods.
The new findings, according to Holland, give further support to that type of eating pattern.
For the study, published online Jan. 29 in Neurology, the researchers followed 921 older adults in an ongoing project looking at aging and memory.
At the outset, they were 81 years old, on average, and answered questions on their diet, other lifestyle habits and medical history. Each year, they underwent neurological evaluations to spot signs of dementia.
Over six years, 220 study participants were diagnosed with probable Alzheimer's. The risk, it turned out, was 48% lower for the one-fifth with the highest flavonol intake, versus the one-fifth with the lowest.
People largely got their flavonols from kale, spinach, broccoli, apples, pears, beans, tomatoes, tea, olive oil and wine. And the 20% percent with the highest intake consumed 15 milligrams (mg) a day, on average -- three times more than people with the lowest flavonol intake, the findings showed.
According to Holland, it doesn't take a full-fledged vegetarian diet to reach the 15-mg mark each day: Half a cup of cooked leafy greens (or one cup of raw), a half-cup of berries, and a half-cup of other cooked vegetables should do it.
Of course, there may be other differences between older adults who eat lots of veggies and those who don't. In this study, people with a high flavonol intake were more educated and more likely to exercise, for example.
But that did not explain their lower Alzheimer's risk, the researchers found. Nor did factors like overall diet, body weight or depression symptoms.
That said, no one is suggesting people should focus on flavonols alone.
Dr. Steven DeKosky is deputy director of the McKnight Brain Institute at the University of Florida, in Gainesville. He said, "This disease is complex, and there's no one thing that will prevent it."
Nor is there any evidence that flavonol supplements curb Alzheimer's risk, stressed DeKosky, who is also a fellow with the American Academy of Neurology.
"But we do think there are things you can do to decrease your risk," he said.
Studies have linked a number of lifestyle factors to a relatively lower risk of developing dementia -- including a healthy diet, regular exercise, staying socially active, and challenging yourself with mentally stimulating activities.
But while studies do statistical adjustments to try to isolate an effect of one thing -- like flavonol intake -- in the real world, it's overall lifestyle that's key, DeKosky said.
"It's not one thing in isolation," he said. "It's more like a symphony."
The Alzheimer's Association has advice on lifestyle and brain health.