The role of lifestyle, cardiovascular factors and biomarkers on health status in older adults at risk of cognitive deterioration
AuthorLai, Michelle Mei Yee
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© 2021 Michelle Mei Yee Lai
Recent developments in neuroscience have heightened the possibilities to tackle the prodromal stage of dementia. The purpose of this thesis is to identify the relationships between physical health, cognitive function, vascular risk burden and peripheral biomarker candidates in 108 older adults at risk of cognitive decline. The AIBL Active trial participants, aged 60 years and older (32 cases of MCI, 76 cases of SMC) with at least one cardiovascular risk factor present, completed a neuropsychological test battery and provided cross-sectional health data and physical activity information using a validated questionnaire and pedometer recordings. Cardiovascular parameters and blood tests determined if the participants met the clinical definition of metabolic syndrome that referred to a cluster of vascular and metabolic disturbances due to obesity and insulin resistance. This thesis utilised a preferred statistical standardisation of metabolic syndrome factors and obtained continuous variable (z-scores) to indicate the composite cardiovascular risk burden that addressed the progressive nature of the syndrome. Regression models adjusted for covariates examined the associations between the parameters and cognitive function. Almost two-thirds of participants met the national physical activity guidelines for older Australians with MCI or SMC (moderate-to-vigorous physical activity (MVPA) over 150 minutes per week), according to self-report (average 317 minutes/week). The pedometer estimated a mean of 6,926 steps/day for all participants. Participants with lower body mass index (BMI) and higher self-efficacy were 18% and 24% respectively more likely to meet the guideline recommendations. The risk severity of metabolic syndrome was inversely associated with pedometer tracked physical activity and the six-minute walk test, independent of global cognitive performance. The six-minute walk test has a stronger association with metabolic syndrome and may be a preferable assessment tool to evaluate exercise capacity compared to the timed-up-and-go test in participants at risk of cognitive decline. The metabolic syndrome components are traditional vascular and metabolic risk factors, but few cognitive studies have examined the combined risk severity. While cognitive tests scores were similar between the two groups with or without a clinical diagnosis of a metabolic syndrome, the continuous standardised z-scores for metabolic syndrome were associated with lower cognitive performance for global cognition and executive functions. Therefore, the combined risk burden (z-score) was more sensitive to cognitive associations than the presence or absence of the clinical syndrome. Multivariate regression analyses showed separate linear associations between vascular risk factors (fasting homocysteine, glucose and Framingham scores) and lower cognitive functions. The importance and originality of this thesis are that several peripheral biomarkers showed significant associations with cognition, including between increasing plasma tumour necrosis factor (TNF-alpha) and executive dysfunction and between increasing brain-derived neurotrophic factor (BDNF) and better global cognition. A model hypothesising the relationship between physical health, cognition, vascular risk factors and biomarkers is proposed. A higher cardiometabolic risk burden may point to opportunities for cognitive testing and lifestyle modification recommendation in older adults as individuals may experience cognitive changes. The findings in the peripheral biomarker analyses add to the evidence of associations between TNF-alpha, BDNF and cognitive deficits. Future longitudinal research will be needed to establish a direct link between health factors, biomarkers and cognitive decline in older adults at risk of cognitive deterioration.
Keywordscognitive impairment; dementia; subjective memory complaints; neurocognitive disorder; cognitive function; physical activity; functional mobility; six-minute walk; cardiovascular risk factors; metabolic syndrome; obesity; peripheral biomarkers; tumour necrosis factor; brain-derived neurotrophic factor
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