By 2050 the number of people aged 60 years and over is projected to reach 2 billion, of which an estimated 131 million will have dementia, therefore there is an urgent need to identify public health strategies aimed at promoting better brain health in our ageing populations. A review of the literature within this thesis identified certain dietary patterns, as well as specific nutrients, which could be beneficial in preventing or delaying the onset of brain disorders, with the strongest evidence supporting roles for folate and metabolically related B-vitamins. The biological mechanism whereby these B-vitamins are linked with the brain is likely related to their crucial roles as co-factors in one-carbon metabolism. The overall aim of the original studies in this thesis was therefore to investigate the impact of folate-related B-vitamins on brain health in older adults recruited to the Trinity, Ulster and Department of Agriculture (TUDA) cohort study. Results from new analysis of existing data from the TUDA cohort (n = 5071) in relation to mental health showed that lower biomarker status of folate (< 1520nmo/L), vitamin B6 (< 51.9nmol/L) or riboflavin (EGRac ≥1.46) were each associated with an increased risk of depression (by up to 80%), while an increased risk of anxiety was found in TUDA participants with a deficient status of vitamins B6 (but not any other B-vitamin). Daily intake of fortified foods was associated with improved B-vitamin biomarker status and a 50% reduction in the risk of depression. A new investigation of the TUDA cohort, the BrainHOP trial (n = 328), identified a protective effect of supplementation with combined folic acid, vitamin B12, vitamin B6 and riboflavin on visuospatial cognitive function. In a pilot study, involving a subset of the BrainHOP cohort (n = 25) who were examined post-intervention using magnetoencephalography, the results suggested a protective effect of B-vitamins on neuronal function. In conclusion, the findings of this thesis have identified the potential importance of optimising B-vitamin status as a means to help achieve better brain health in older people, which in turn could have a significant impact on public health and associated costs in ageing populations.
