UNDERSTANDING COGNITIVE CHANGES IN OLDER ADULTS WITH SUBJECTIVE COGNITIVE DECLINE: THE ROLES OF SLEEP DISTURBANCE AND PHYSICAL FRAILTY

Background: Subjective cognitive decline (SCD), defined as self-perceived cognitive decline in the absence of objective impairment, is increasingly recognized as a potential early indicator of Alzheimer’s disease and related dementias. However, little is known about how older adults experience SCD in daily life, and whether sleep disturbance and physical frailty contribute to cognitive progression in this population. The purpose of this dissertation is to advance understanding of cognitive changes in older adults with SCD and to examine the roles of sleep disturbance and physical frailty in future cognitive decline. Methods: This dissertation employed a multi-method design, including a qualitative study and two quantitative studies. The qualitative study involved semi-structured interviews with 16 community-dwelling older adults with SCD to understand their daily life experiences related to cognitive changes. The quantitative studies used six-wave data (2010–2020) from the Health and Retirement Study, focusing on adults reported SCD at baseline. We examined (1) the association between baseline sleep disturbance and 10-year trajectories of global cognitive performance, (2) the associations of sleep disturbance and physical frailty with incident cognitive impairment and dementia, (3) the moderating role of physical frailty in the association between sleep disturbance and cognitive outcomes. Results: Older adults with SCD reported noticeable changes in attention, memory, and executive function in their daily lives, often accompanied by negative emotions such as frustration, worry, and embarrassment. Poorer sleep was significantly associated with faster cognitive decline among adults aged ≥65 years, but not in adults aged 50–64. While sleep disturbance was not independently associated with incident cognitive impairment or dementia, baseline prefrailty/frailty was significantly associated with increased risks of cognitive impairment and dementia. A moderating effect was observed: poorer sleep was more strongly associated with incident cognitive impairment among non-frail older adults than among those prefrail or frail. Conclusion: This dissertation provides new insights into the lived experiences of older adults with SCD and the contributions of sleep disturbance and physical frailty to their cognitive progression. The findings support the development of early, non-pharmacological interventions targeting sleep and physical frailty to prevent or delay cognitive decline in this population.