U-shaped association between sleep duration and subjective cognitive complaints in Chinese elderly: a cross-sectional study.

Background: Subjective cognitive decline (SCD) may be the early screening signal to distinguish susceptible population with Alzheimer's disease (AD) and mild cognitive impairment (MCI). Subjective cognitive complaints (SCCs) have been proved strongly associated with SCD. This study aimed to explore the association between sleep duration and SCCs in the Chinese elderly.

Methods: We conducted a cross-sectional study involving 688 participants aged 60 years and older in Guangdong Province, China. SCCs were assessed by the Subjective Cognitive Decline questionnaire 9 (SCD-Q9), which contained 9 items with two dimensions, including the overall memory function and time comparison (OMTC) and daily activity ability (DAA). Restricted cubic splines and generalized additive model (GAM) were used to fit the association between sleep duration and SCD-Q9 score.

Results: There were significant U-shaped associations between sleep duration and overall score of SCD-Q9 (EDF = 3.842, P < 0.001), as well as the OMTC dimension (EDF = 4.471, P < 0.001) in the age- and gender-adjusted GAM. The lowest points on the overall score of SCD-Q9 and OMTC score were observed in those sleeping 8 h per night. After further adjusting for other demographic characteristics, lifestyle behaviors, hypertension and diabetes, the U-shaped associations between sleep duration and the overall score of SCD-Q9 (EDF = 3.575, P = 0.004), sleep duration and the OMTC score (EDF = 4.478, P = 0.010) were still found. The daily activity ability (DAA) score was also non-linear associated with sleep duration both in the age- and gender-adjusted GAM (EDF = 2.314, P < 0.001) and further adjusted GAM (EDF = 2.080, P = 0.010).

Conclusions: Both longer sleep duration (> 8 h) and shorter duration (< 8 h) were linked to worse SCCs. Future studies should explore the protective effect of managing sleep duration on SCD and its progression to dementia.