Graduate Thesis Or Dissertation


Does Hemoglobin A1c Influence the Relationship between Stressful Life Events and Cognition in Later Life? Findings from the VA Normative Aging Study Public Deposited

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  • With Type 2 diabetes sharply growing in prevalence around the world, there has been an increased interest in adverse health outcomes resulting from excessively high blood sugar and the associated damage to blood vessels, increasing the risk of a variety of chronic illnesses and mortality. If untreated, high blood sugar can result in increased hemoglobin A1c (HbA1c), which can damage veins and arteries for the duration of these erythrocytes’ lifespan, resulting in accumulative damage and loss of efficiency of the circulatory system. Both HbA1c and stressful life events (SLEs) have demonstrated independent effects on cognition in late life, with higher levels of both stress and HbA1c impairing cognition. SLEs can influence a variety of physiological pathways, including HbA1c, thus it is possible that HbA1c can moderate the influence of SLEs on cognitive function. The present study investigated the mediating and moderating effects of HbA1c on the relationship between SLEs and cognitive outcomes in late life. Both global and fluid cognitive measures to investigate general and domain-specific declines associated with both SLEs and HbA1, and then age stratified these same analyses to examine whether the old-old (75+) are more vulnerable, will be used to investigate the potential relationships between these variables. The sample consisted of older adult males (N = 578) from the VA Normative Aging Study (M age = 74.3 years, SD = 6.5) . Structural equation models showed that both SLE and HbA1c exhibited direct effects that varied depending upon the cognitive outcome and type of analysis. However, SLE and HbA1c were unrelated in this sample, therefore no mediation effects were found. One moderation effect was found for the pattern recognition task in the general sample; however the interaction was in the opposite effect of the direct effects, and further investigation suggested a multicollinearity problems, potentially nullifying this result. The analyses stratified by age (< 75 and 75+) yielded some interesting results. Within age group, age was consistently an inversely associated with MMSE and word list total recall, but no significant relationship to verbal fluency and pattern recognition in the old-old group, suggesting either plateau effects, survivor effects, or potentially a specific vulnerability. Further, education appeared to be more protective against cognitive deficits in the old-old group when compared to the young-old group, and HbA1c was more consistently inversely related to cognition in the old-old group, while stress was more likely to have a significant relation in the young-old group. One moderation model for verbal fluency was significant for the old-old group, and results suggested that those high in HbA1c and SLE had lower scores for verbal fluency. Future research should be conducted with more diverse samples, and better aligning the timing of the stress and HbA1c assays. The implications of this work include, bolsters our understanding of how joint effects of physiology and stress may influence specific domains of cognitive function in aging, perhaps resulting in accelerated aging.
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