The global human population is collectively aging, to an unprecedented extent. This rise in the average age of humans is accompanied by increases in the prevalence of and social burden related to cognitive impairment. Dietary flavonoids have demonstrated considerable neuroprotective qualities in research, yet past epidemiologic studies examining the effects of flavonoid consumption on the development of dementia and other cognitive conditions have shown inconsistent results.
Part of this challenge lies in the fact that dementia typically has a lengthy preclinical phase—often twenty years or more—during which individuals may subjectively be aware of subtle alterations in their own cognitive function before the appearance of overt clinical change. Subjective cognitive decline (SCD) has been found to relate strongly to objective cognitive changes as well as subsequent cognitive decline. For these reasons, assessing dietary flavonoid intakes through the decades prior to clinically observable modification of cognitive function may present a more meaningful approach to investigating their later-life effects.
This prospective study is one of the largest and longest to examine flavonoid intakes and cognitive health, and involved 49,493 female registered nurses (aged 30-55 years at baseline) from the Nurses Health Study (NHS) as well as 27,842 male health professionals from (aged 40-75 years at outset) from the Health Professionals Follow-Up Study (HPFS). NHS participants were followed from 1984 to 2014; HPFS participants from 1986 to 2012. Dietary information was collected from study subjects according to validated procedures each two to four years for over 20 years. SCD was assessed by validated questionnaires twice in the final two to four years of the investigation, when participants’ mean ages were 76.3 years among females and 73 years among males. Dietary data on flavonoid intakes were derived from federal database values, and focused on six subtypes of flavonoids:
● Flavones (such as luteolin and apigenin)
● Flavanones (like hesperetin and naringenin)
● Anthocyanins (delphinidin, pelargonin, etc.)
● Flavonols (like quercetin and kaempferol)
● Flavan-3-ol monomers (catechins, epicatechins, etc.)
● Flavonoid polymers (such as proanthocyanidins and tannins)
Study subjects were classed into age-controlled quintiles of consumption level for total flavonoids as well as the flavonoid subtypes. Results were controlled for age, body mass index, physical activity level, and numerous other relevant health, dietary, and lifestyle factors.
Dietary Flavonoid Intakes Impact Self-Assessment of Cognitive Decline
Subjective cognitive decline has previously been linked to the incidence of clinical cognitive disorders. Results from this comprehensive and well-designed study suggest that regular, generous consumption of flavonoid-rich foods (like berries, cruciferous vegetables, and citrus fruits) is associated with better subjective cognitive function later in life.