The Role of Race-Gender Intersectionality in Associations between Insomnia Patterns and Late-Life Memory Trajectories

Introduction
Difficulty initiating sleep (DIS) may be a stronger predictor of neurodegenerative risk than other insomnia symptoms. This study examined whether longitudinal patterns of DIS are associated with subsequent memory trajectories, and whether associations differ across non-Hispanic Black and White men and women.

Methods
12,565 participants in the Health and Retirement Study (Mage=67.8±9.1, 59.1% women) who self-identified as non-Hispanic Black (14.5%) or non-Hispanic White were included. DIS (“How often do you have trouble falling asleep?”) at three biennial waves (2002-2006) was dichotomized (“never/rarely/sometimes”=0, “often”=1). Participants were categorized into three mutually exclusive groups: low (reference group), persistent, and variable DIS. Episodic memory was assessed using a 10-item word list recall test at five biennial waves (2008-2016). Latent growth curves modeled associations between DIS patterns and subsequent memory level and change, adjusting for sociodemographics (model 1), health conditions (model 2), and depressive symptoms (model 3) in 2002. Stratified models compared associations across White men, Black men, White women, and Black women.

Results
Compared to low DIS, persistent (β=-0.03, p<.001) or variable (β=-0.07, p<.001) DIS was associated with worse subsequent memory in models 1 and 2. The effect of variable (β=-0.05, p<.001), but not persistent (β=-0.01, p=.271), DIS remained in model 3. Persistent DIS was most prevalent among White women (5.4% vs. 2.4-4%), and variable DIS was most prevalent among Black women (24.1% vs. 14-22.2%). Persistent DIS was only significantly associated with memory among White women (β=-0.04, p=.003 vs. β=-0.04, p=.324 for Black Men; β=-0.03, p=.087 for White men; and β=0.01, p=.859 for Black women). Variable DIS was most strongly associated with memory among Black men (β=-0.141, p=.003), followed by White men (β=-0.09, p<.001), White women (β=-0.06, p<.001) and Black women (β=-0.06, p=.064). There were no associations between DIS patterns and memory change.

Conclusion
While links between persistent DIS and subsequent memory may reflect negative cognitive effects of depression, variable DIS may presage worse memory above and beyond depression. Race/gender differences in the prevalence and predictive value of DIS patterns for subsequent cognitive function highlight the value of an intersectional lens. Gender disparities in DIS may be more prominent than racial disparities.