In 2 prospective observational studies, the consumption of fruit and vegetables with a high flavonoid content was associated with a slower subjectively experienced cognitive decline in old age. A team led by Walter Willett from Harvard University in Boston analyzed the data of 49,493 women from the “Nurses Health Study” and 27,842 men from the “Health Professionals Follow-up Study”. Since the start of the study (1984 and 1986), the study participants were regularly questioned about their eating habits and interviewed twice about their subjective cognitive decline. The study authors were able to show that subjective cognitive impairment was associated with a low consumption of flavonoids. The strongest possible protective effect was found for flavones, flavanones and anthocyanins. Flavanones are found particularly in tropical fruits such as grapefruit.
Objective: To prospectively investigate the association between long-term dietary flavonoid intake and subjective cognitive decline (SCD). Methods: 49,493 women from the Nurses’ Health Study (NHS) (1984-2006) and 27,842 men from the Health Professionals Follow-Up Study (HPFS) (1986-2002) were examined. Poisson regression was used to examine the association between dietary intake of flavonoids (flavonols, flavones, flavanones, flavan-3-ols, anthocyanins, polymeric flavonoids and proanthocyanidins) and subsequent SCD. For the NHS, long-term average dietary intake was calculated using seven repeated semiquantitative food frequency questionnaires (SFFQs), and SCD was assessed in 2012 and 2014. For the HPFS, mean dietary intake was calculated using 5 repeated SFFQs, and SCD was assessed in 2008 and 2012. Results: Higher intake of total flavonoids was associated with lower odds of SCD after adjusting for age, total energy intake, major non-nutritional factors, and specific dietary factors. When comparing the highest to lowest quintiles of total flavonoid intake, the pooled multivariable-adjusted odds ratio (OR) for a 3 unit increase in SCD was 0.81 (95% confidence interval [CI] 0.76, 0.89). In the pooled results, the strongest associations were observed for flavones (OR 0.62 [95% CI 0.57, 0.68]), flavanones (0.64 [0.58, 0.68]) and anthocyanins (0.76 [0.72, 0.84]) (p-trend <0.001 for all groups). The dose-response curve was steepest for flavones, followed by anthocyanins. Many flavonoid-rich foods such as grapefruits, strawberries, oranges, citrus juices, apples/pears, celery, peppers and bananas were significantly associated with a lower risk of SCD. Our results suggest a benefit of higher flavonoid intake for the preservation of cognitive function in US men and women.