Q: Of the nutrients in plant foods, it seems like flavonoids might be special regarding brain health. What do we know?
A: Science already touts heart-health benefits of plant-based diets like the Mediterranean, MIND and DASH diets. Researchers are discovering how plant-based eating also may an important role in cognitive fitness and perhaps help prevent dementia, including Alzheimer’s disease.
And one class of nutrients in plants continues to stand out: flavonoids. They have six subclasses: anthocyanidins, flavan-3-ols, flavanones, flavones, flavonols, and polymers. A variety of fruits and vegetables contain flavonoids. Some of the highest amounts are in berries, apples, citrus fruit (oranges, lemons), grapes, spinach, legumes, kale, broccoli, soybeans, onions, tea, cocoa, and wine. Some foods contain only one subclass of flavonoids, while others have several.
Researchers believe flavonoids may help the brain in several ways. For instance, studies suggest they reduce cell-damaging free radicals and soothe inflammation. Some early-stage animal studies have shown that flavonoids can block beta-amyloid plaque buildup in the brain, a trademark of Alzheimer’s.
Flavonoids also may enhance brain blood flow. Some studies found flavonoid intake is inversely related to cardiovascular disease, and what is good for the cardiovascular system is also good for the brain.
Large human studies of flavonoids are still in their early phases, but initial findings show promise. One of the most substantial to date was a recent study linking high flavonoid intake and a lower risk of Alzheimer’s and related dementias (conditions with symptoms similar to Alzheimer’s). The results were published online April 22, 2020, by The American Journal of Clinical Nutrition.
Using data from the Framingham Heart Study, researchers looked at the dietary habits of almost 3,000 people, average age 59, without any signs of dementia. Over 20 years, people with the highest daily intake of flavonoids (about 297 milligrams) had a lower risk of developing Alzheimer’s or a related dementia than those who ate the smallest amounts (about 123 milligrams).
Still, the link between flavonoids and brain health might be a matter of coincidence. It may take a team effort from all kinds of nutrients, but flavonoids may be one of the main players.
How much is enough? There is no definite recommended daily intake for flavonoids. Three servings of vegetables and two servings of fruits a day is the commonly suggested goal. The more colors and types of food you can put on your plate for every meal, the better. That should be a good start to give you the flavonoids your body — and brain — may need.
(Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)
In this Series
- 7 updates