Flavonoids are a group of naturally occurring compounds found in plants and are consumed in the form of fruits, vegetables, or plant-derived products, such as tea, wine, and dark chocolate. (In general, the content of flavonoids is highest in more pigmented foods, such as berries, citrus fruits, kale, and red cabbage.) We have long been interested in the beneficial health effects of flavonoids, and they have been described as having anti-oxidative, anti-inflammatory, anti-mutagenic and anti-carcinogenic properties. Because flavonoids are powerful antioxidants, there is considerable interest in the capacity of flavonoids to protect against oxidative stress which has been associated with age-related cognitive decline.
Data regarding the cognition-sparing effects of flavonoids have been somewhat murky. Several small, short-term intervention trials support the beneficial effects of flavonoids for reducing cognitive decline; however, larger epidemiological studies have been inconclusive. A recent study from Deborah Blacker, MD ScD, Director of the Gerontology Research Unit at MGH, and her colleagues at the Harvard T. H. Chan School ofPublic Health analyzed data from two large cohorts to evaluate the impact of dietary flavonoid intake on subjective cognitive decline.
Subjective cognitive decline (SCD) refers to self-perceived cognitive decline which, even without objectively measurable cognitive impairment, can be a precursor to dementia. Because SCD may appear years before the onset of more significant cognitive impairment is apparent, the identification — and prevention — of SCD may help to decrease risk for more significant cognitive impairment in vulnerable populations.
The researchers were able to take advantage of two large prospective cohort studies following men and women in the US for nearly three decades: 49,493 women from the Nurses’ Health Study (NHS) and 27,842 men from the Health Professionals Follow-up Study (HPFS). The researchers estimated the intake of flavonoids (flavonols, flavones, flavanones, flavan-3-ols, anthocyanins, polymeric flavonoids, and proanthocyanidins) using questionnaires asking participants to provide details regarding their dietary intake of various foods. Their analysis evaluated the association between intake of dietary flavonoids and subsequent subjective reports of cognitive decline.
The mean age of participants at the initial SCD assessment was 76.3 years for women in the NHS and 73 years in men in the HPFS study. Individuals reporting higher total intake of flavonoids were less likely to report subjective cognitive decline. Comparing individuals with the highest versus the lowest quintiles of total flavonoid intake, the adjusted odds ratio (aOR) for SCD was 0.81 (95% CI 0.76-0.89). In the pooled analysis, certain flavonoids were more strongly associated with decreased risk for cognitive decline: flavones (OR=0.62), flavanones (0.64), and anthocyanins (0.76). For example, individuals consuming higher levels of flavones were nearly 40% less likely to report cognitive decline, which is like being 3 to 4 years younger in terms of cognitive age. Certain flavonoid-rich foods, such as strawberries, oranges, grapefruits, citrus juices, apples/pears, celery, peppers, and bananas, were significantly associated with lower odds of reporting SCD.
This is the largest study to date evaluating the impact of dietary flavonoids on cognitive decline. Because of the size of the cohorts analyzed in this study, the researchers were able to control for a number of potential confounding factors, including dietary factors (e.g., use of vitamins, overall protein intake) and non-dietary factors associated with cognitive decline (ie., socioeconomic status, smoking). While this study did not use objective measures of cognitive functioning, SCD can be a marker for those at increased risk for further cognitive decline.
In terms of reducing risk of dementia, it is essential that we identify those at increased risk for cognitive decline and develop interventions which reduce risk of dementia or mitigate the severity of its symptoms. Diet has long been considered a modifiable risk factor for dementia, and we emphasize the importance of having a healthy diet as a means of promoting physical and mental health. This study contributes to the weight of evidence that diet is a modifiable risk factor for dementia, and that a diet rich in colorful fruits and vegetables may promote long term brain health.
Read More
Yeh TS, Yuan C, Ascherio A, Rosner B, Willett W, Blacker D. Long-term Dietary Flavonoid Intake and Subjective Cognitive Decline in US Men and Women.Neurology. 2021 Jul 28:10.
