Development and application of flavonoid intake assessment methods and the impact of flavonoids on cognitive and physical outcomes

A growing body of evidence suggests that a diet rich in flavonoids, naturally occurring plant-based compounds, is associated with improved health outcomes. However, current knowledge relating to the measurement of dietary flavonoid intake is limited and studies assessing the association of flavonoid-rich food supplementation with cognitive and physical health outcomes are scarce. This doctoral thesis outlines six studies that were developed to address two main research questions. Firstly, what methods should be employed to measure flavonoid intake? Secondly, how does the consumption of dietary flavonoid impact cognitive and physical outcomes?

In order to associate the impact of dietary flavonoids on health outcomes, accurate dietary assessment is fundamental. A systematic literature review evaluates the various methods employed by current literature to measure flavonoid intake. The review emphasises the reliance of studies utilising unsound dietary assessment methods to measure flavonoid intake and demonstrates that few studies utilise objectives biomarkers as a measure of flavonoid intake.

Dietary flavonoid intake estimates in Australia are limited, and specifically the estimations of flavonoid intake in older Australians are inadequate. A Food Frequency Questionnaire for the measurement of dietary flavonoid intake in this cohort was developed, based on secondary data analysis of detailed dietary information in older adults. The tool is validated against food records and assessed for reliability in a group of older Australians, showing to be a relatively useful instrument to measure flavonoid intake.

In response to the lack of biomarker data utilised in current flavonoid research, a sensitive and specific GC-MS method was developed to determine flavonoids and phenolic acids in biological samples. The developed method has potential to measure 115 flavonoid-related biomarkers in various biological samples, and is applied in later studies of this thesis.

A second systematic literature review identifies a paucity of research regarding foodbased anthocyanin (a subclass of flavonoids) consumption and cognitive outcomes. Various methodological limitations in published studies are highlighted, including a lack of information regarding dosage and dose-timings, age related variations in responses and small sample study sizes. The findings are utilised inform the development of acute and longer-term intervention studies to assess the impact of a flavonoid and anthocyanin-rich cherry juice supplementation on cognitive and physical outcomes.

A pilot cross-over study assesses the acute effects on cognition, blood pressure and plasma biomarkers associated with consumption of a 300ml cherry juice, provided either as a single quantity or as 3x100ml doses administered over 2h. In young adults, older adults, and older adults with dementia similarly, results indicated that the acute impact of anthocyanin-rich cherry juice consumption on cognition was not supported, but a dose-timing administration effect may influence blood pressure outcomes.

A longer-term intervention assesses whether daily consumption of anthocyanin-rich cherry juice changed cognition and blood pressure in older adults with dementia over 12-weeks. The results indicate that anthocyanin-rich cherry juice consumption improve cognitive performance and significantly reduced blood pressure. This study provides the first evidence that a feasible serving of flavonoid-rich food may have beneficial consequences in older adults with Alzheimer’s type dementia.

Overall, this doctoral thesis provides a number of contributions to the literature. Primarily it demonstrates that the dietary flavonoid intake measurement strategies are lacking and the novel tools developed by this thesis improve upon current methods with potential application in future research. Additionally, the findings of the flavonoid intervention trials support the indication that flavonoid, and especially anthocyanin-rich food consumption, may be beneficial for cognitive and physical outcomes.