Year: 2020
Type: dissertation
Abstract: Dementia is a syndrome in which there is deterioration in memory, thinking, behavior and the ability to perform everyday activities. Although dementia affects older people mostly, it is not a normal aging process. Only 16% of seniors receive regular cognitive assessments during routine health check-ups, with Alzheimer’s Disease (AD) and other related dementias contributing to 1 in 3 senior deaths. This is a greater number than breast cancer and prostate cancer combined. Prevention, or early diagnosis can improve the quality of life for people with dementia and their families. It is expected that over the next 30 years the prevalence of AD will continue to rise and the number will double by 2050. As dementia impacts many individuals in such a negative way that ultimately disallows quality of life, it is of utmost importance to investigate modifiable risk factors of dementia that occur, and change, throughout the lifespan in order to alleviate the risk of cognitive impairment that may ultimately lead to Alzheimer’s dementia. Important to this notion is sleep. Sleep has many components that comprise its structure, and has shown to be an important target for intervention to improve health and specifically cognitive function. Both cross-sectional and longitudinal studies have shown short and long sleep duration have been associated with cognitive impairment as well as poor sleep quality. Of note, there are some studies that have shown null findings when comparing sleep behaviors with cognitive outcomes. The mixed findings may be caused by heterogeneity in study populations and sleep measurement methods warrant further investigation, particularly longitudinal studies that can better clarify the temporal relationships between sleep and cognitive outcomes. The addition of studies including middle-aged adults in analysis is important as this is a critical life period linked with later dementia risk. Moreover, there are no data available to our knowledge that includes actual AD confirmed deaths within analysis, only markers of Alzheimer’s Disease. This study investigated two large samples of U.S. men and women followed over a number of years and analyzed from both cross-sectional and prospective perspectives. The use of the Midlife in the United States (MIDUS) Study and the National Institutes of Health-American Association of Retired Persons-Diet and Health Study (NIH-AARP-Diet and Health Study) datasets were included. For MIDUS analysis, both subjectively measured sleep (weekday and weekend duration, difference in duration, and sleep quality), as well as objectively measured sleep (Total Sleep Time (TST), Wake after sleep onset (WASO), Sleep Efficiency (SE), and Sleep Latency (SL)) were included as exposure variables. The outcome measure of cognitive scores (cross-sectional) and change in cognitive scores (prospective) were obtained via Brief Test of Adult Cognition by Telephone (BTACT) were administration. Composite, Episodic Memory (EM), and Executive Function (EF) scores were calculate from the results of the BTACT. Beta coefficients and 95% CL were used for statistical analysis. For the NIH-AARP Diet and Health Study, self-reported sleep duration (<5, 6-7, 7-8, 9+ hours) and napping duration (none, less than 1 hour, 1+) were obtained via questionnaire. The outcome measure was Alzheimer’s Disease death which was confirmed by death records. Hazard Ratios (HR) and 95% CI were used for statistical analysis. The main findings of our results for the MIDUS study demonstrated a cross-sectional association between self-reported long sleep duration (>8 hours/night) and lower composite cognitive scores (p=0.01), and the association was stronger among men and for weekend sleep (β (95% CL)): (-0.17 (-0.29, -0.06)). Additionally, EM was negatively associated with longer sleep duration on both weekdays and weekends ((-0.07 (-0.18, 0.04)); p=0.01 and (-0.06 (-0.14, 0.02)); p=0.02 respectively) for cross-sectional results. Moreover, EF was lower in the overall analysis in individuals sleeping >8 hours/night (-0.13 (-0.24, -0.03)), particularly in men (-0.13 (-0.24, -0.02)). There were no statistical significant prospective associations between self-reported sleep variables and cognitive function. Objectively measured sleep in the MIDUS study was not cross-sectionally associated with cognitive outcomes, however, in prospective analyses <6 hours TST was associated with greater decline in EM scores (-0.42 (-0.71, -0.13)) compared to referent group of 6-7 hours TST. Interestingly, for WASO, there was a significant trend (p=0.02) suggesting an association between more WASO and less decline in EM (0.40 (0.02, 0.78)), comparing >60 with <32 min WASO. In the NIH-AARP Diet and Health Study, results demonstrated that 9+ hours of sleep was associated with 50% increase in AD mortality risk when compared to the reference group (7-8 hours) (HR (95% CI) 1.50 (1.17, 1.92). Further adjusting for daytime napping (Model 3) slightly attenuated the associations for 9+ hours (1.47 (1.15, 1.88)) but the results remained statistically significant. In sensitivity analysis where AD deaths within the first 5 years were removed to avoid reverse causation, results remained significant in our main model (1.46 (1.12, 1.90)) and when adjusting for napping (1.43 (1.10, 1.87)). Sex specific analysis revealed that the association between 9+ hours of sleep and higher AD mortality was stronger in men (1.53 (1.11, 2.15)) than in women (1.37 (0.91, 2.05)). We also found that individuals reporting napping for 1+ hour/day had higher risk of AD death (HR (95%CI)) (1.29 (1.08, 1.55)), which compared to those with no napping, and additionally adjusting for nighttime sleep duration and removing AD deaths within 5 years after baseline had little impact on this association. Results from this study demonstrate that there are many aspects of sleep associated with cognitive outcomes as well as increased risk in AD-specific death. The findings from this study suggest that sleep plays an important role in the changes to cognitive function and AD over the lifespan, and the sleep is a possible target for interventions to address in future studies.
DOI: 10.17077/etd.005345
Language: English
Subfield: Psychiatry and Mental health
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W4233761251