New study shows slower cognitive decline with flavonoids. Know which foods are recommended
Eating more flavonoids, the antioxidants found in many vegetables, fruit, tea and wine, may slow the rate of memory loss, claims a new study.
The cognitive scores of people in the study who ate the most flavonoids declined 0.4 points per decade slower than the scores of people who ate the least flavonoids. The results held even after adding other factors that can affect memory, such as age, gender and smoking, according to the study recently published in Neurology, the medical journal of the American Academy of Neurology.
“It is exciting that our study shows that making specific dietary choices can lead to a slower rate of cognitive decline,” study author Dr. Thomas Holland, professor in the department of internal medicine at Rush University School of Medicine in Chicago.
“Something as simple as eating more fruit and vegetables and drinking more tea is an easy way for people to take an active role in maintaining their own brain health.”
Flavonoids are cytoprotective, meaning they protect cells, including neurons, so it’s plausible that there’s a direct impact on cognition, said Dr. David Katz, an expert in preventive medicine, lifestyle and nutrition, who was not involved in the study.
Onions contain the highest levels of quercetin, one of the most common flavonoids.
“But they’re also an indicator of more fruit and vegetable intake – which is good for the brain because it’s good for all the vital organs and the body as a whole,” Katz said in an email.
“It can also be an indicator of better overall diet quality or even greater health awareness. More health-conscious people might do things to preserve their cognition, or perhaps being more health-conscious is a by-product of better cognition.”
A huge family of phytochemicals
Plants contain over 5000 flavonoid compounds, which play a variety of roles in cell growth, combating environmental stress, and attracting insects for pollination.
Flavonols, a type of flavonoid, have been shown in animal and some human trials to reduce inflammation, a major trigger for chronic disease, as well as being a very rich source of antioxidants. Antioxidants fight free radicals, the “highly unstable molecules that form naturally when we exercise and when the body converts food into energy,” according to the National Center for Complementary and Integrative Health, part of the National Institutes of Health.
One of the most common flavonols, quercetin, has shown promising results in reducing the onset of colorectal cancer and other types of cancer, according to studies. Onions contain the highest levels of quercetin. Lower levels can be found in broccoli, blueberries, cauliflower, cabbage, leeks, spinach and strawberries.
Another common flavonol, kaempferol, appears to inhibit the growth of cancer cells while preserving and protecting normal cells. Good sources of kaempferol are onions, asparagus and berries, although the richest vegetables are spinach, kale and other green leafy vegetables, as well as some herbs such as chives, dill and tarragon.
A third key player is myricetin, which has been studied in rodents for blood sugar control and the reduction of tau, a protein that causes the tangles characteristic of Alzheimer’s disease and other dementias. Spinach and strawberries contain high levels of myricetin, but honey, black currants, grapes and other fruits, berries, vegetables, nuts and tea are also good sources.
The last group of flavonols, isoramnetin, may protect against cardiovascular and neurovascular disease, in addition to having benefits against tumors and anti-inflammatory properties. Good sources of isoramnetin are pears, olive oil, wine and tomato sauce.
You can find a complete list of the flavonoid content of various fruits and vegetables here [em inglês].
An older, dementia-free population
The new study asked 961 people with an average age of 81 and no signs of dementia to complete a dietary questionnaire every year for seven years. In addition, participants underwent annual cognitive and memory tests and were asked about the time they spent physically and mentally active.
People were divided into groups based on their daily consumption of flavonoids. The lowest intake was about 5 milligrams per day; the higher value of 15 milligrams per day is the equivalent of about one cup of dark leafy greens, the study noted. (As a point of comparison, the average intake of flavonoids in adults in the US is about 16 to 20 milligrams a day, according to the study.)
The study looked at the impact of the four main flavonols – kaempferol, quercetin, myricetin and isoramnetin – on the rate of cognitive decline over seven years.
The biggest impact was with kaempferol: People who ate the highest amounts of kaempferol foods had a 0.4 point slower rate of cognitive decline per decade compared to those who ate the least, the study found.
Myricetin was close behind: People who ate the most myricetin foods had a 0.3 point slower rate of cognitive decline per decade compared with the lowest intake group. People who ate the most quercetin-containing foods showed a 0.2 point slower rate of cognitive decline per decade.
Dietary isoramnetin had no impact, the study found.
The jury is still out
Despite the apparent positive aspects, studies on the impact of flavonoids on human health have been inconclusive – mainly because many are observational and cannot show direct cause and effect. This also applies to the study in Neurology, according to its authors.
A few randomized clinical trials – the scientific gold standard – have shown benefits associated with flavonoids for controlling blood sugar in type II diabetes and improving cardiovascular health, according to the Linus Pauling Institute, home to the Micronutrient Information Center, a online database for nutritional information.
Whether these benefits will be long-term is unknown, the Institute said, and no clear impact has been demonstrated on cancer prevention or cognitive protection.
“There are other bioactives that may contribute to the observed results,” said Katz. “Further studies are needed to fully isolate the effects of flavonoids.”
There’s also a downside to assuming a health impact without the necessary studies to back it up, said Dr. Christopher Gardner, research professor of medicine and director of the Nutrition Studies Research Group at Stanford University.
“We know that Americans will want the benefits of plants, but they won’t want to eat them,” he said in an email.
“(And) if people read the header and ran out to buy bottled flavonoids (extracts) instead of eating the vegetables, they might discover that it wasn’t just the flavonoids, but the whole of everything those plants contain.”