Investigating the relationship between diet, lifestyle and healthy brain ageing

  • Rebecca Townsend

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Introduction
Dementia is a neurodegenerative condition for which there is currently no cure. Expansion of the ageing population in the 21st century means that incidence of dementia is projected to treble by the year 2050. However, up to 40% of future dementia cases could be delayed or prevented by addressing modifiable factors, some of which, include physical inactivity, obesity and hypertension. Accumulating evidence suggests diet may play a crucial role in reducing risk of both dementia and the condition of cognitive decline (which it is often preceded by). Furthermore, as dementia is multi-aetiological and complex, combining multiple protective factors (e.g., diet and physical activity) within a lifestyle approach has also been proposed to potentially reduce risk. As a result, it is important to investigate the influence of diet on cognition and further explore how diet may be incorporated into a lifestyle approach which promotes healthy brain ageing.

Aim
The aim of this thesis is to explore the relationship between diet, lifestyle and healthy brain ageing, to inform our understanding of preventative opportunities throughout the adult life-course.

Methods
A broad systematic review was firstly conducted to synthesise current evidence of the associations between, and effects of, dietary patterns (DP) on cognitive decline, cognitive disorders (Chapter 2) and neuroimaging markers (Chapter 3). To understand how diet could be promoted as part of a wider lifestyle to reduce dementia risk, it was firstly important to examine public understanding surrounding brain health. Therefore, a cross-sectional, online survey was developed (Chapter 4), and evaluated (Chapter 5) to explore awareness, beliefs and behaviours surrounding brain health and lifestyle, among adults aged over 40 years old across the UK and Ireland. To then understand the practical application of a lifestyle intervention which aimed to reduce risk of dementia among a high-risk Irish population, the final chapter in this thesis (Chapter 6) involved a mixed-methods evaluation of a multi-domain pilot RCT titled ‘Brain-Diabetes’.ResultsResults from the systematic review identified 83 prospective studies and ten randomised control trials (RCT) which contained outcomes of cognitive decline or cognitive disorders (Chapter 2), and nine prospective studies with neuroimaging outcomes (Chapter 3). In total, 52% and 67% of prospective studies reported a beneficial association between ‘healthy’ DPs and outcomes of cognitive decline and cognitive disorders, respectively. Among RCT studies, 50% found a positive effect of a healthy diet on cognitive decline and the one RCT which examined risk of cognitive disorder was within a sub-group analysis. Results in relation to neuroimaging markers highlighted promising associations between the Mediterranean diet and brain function and structure, but evidence was inconsistent. Overall, the review illustrated substantial between-study heterogeneity across the evidence base and highlighted the need to standardise measurement of both exposure (DPs) and outcomes to progress future studies within the field.The target population for the Brain Health and Lifestyle Survey were individuals aged ≥40 years old, living across the UK and Ireland. The survey was co-developed with public and patient involvement (PPI) and based on existing literature, behavioural frameworks and validated scales to assess relevant behaviours (Chapter 4). Results presented in Chapter 5 suggested low public awareness of some modifiable factors and identified main motivators (noticing problems with brain health, provision of information about brain health) and barriers (lack of enjoyment and knowledge) to improving brain health through a lifestyle approach. There were key differences in awareness, behaviours and beliefs surrounding brain health dependent on demographic characteristics, thus highlighting the need to individualise future approaches to promoting brain health.The mixed-methods process evaluation of the multi-domain Brain-Diabetes pilot trial in Chapter 6 demonstrated that a multi-domain intervention was mostly perceived as acceptable and feasible from participants’ perspective. However, the acceptability of the cognitive training component was mixed. Similar to results of Chapter 5, findings conclusively highlighted the need for interventions to be appropriately tailored to promote adherence. Facilitators to trial acceptability were related to self-efficacy, positive affective attitude and intervention coherence. As a result, future work should consider these constructs to improve intervention adherence and acceptability.

Conclusion
The work presented within this thesis provides a novel and valuable contribution to the evidence base of diet and lifestyle approaches to promoting brain health. There are several considerations for future research arising from this work, this includes the importance of standardising the study of DP and developing surrogate measures of cognition. Above all, to tackle the challenge of an ageing population and increasing prevalence of cognitive decline, there is a critical need to increase awareness and promote behaviour change to a ‘brain-healthy lifestyle’ via cost-effective interventions.

Thesis embargoed until 31st July 2024
Date of AwardJul 2023
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorJayne Woodside (Supervisor) & Claire McEvoy (Supervisor)

Keywords

  • brain health
  • dietary patterns
  • dietary intervention
  • multi-domain
  • cognition
  • cognitive health

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