Too little, too much sleep tied to cognitive complaints in Chinese elderly

Both longer (>8 hours) and shorter (<8 hours) sleep duration are significantly associated with worse subjective cognitive complaints (SCCs) in Chinese elderly, according to a cross-sectional study.

In the study, data were collected from 688 individuals aged ≥60 years (mean age, 73.79 years; male, 37.65 percent) living in Guangdong, China, through a face-to-face health interview. SCCs were assessed by the subjective cognitive decline questionnaire 9 (SCD-Q9), which contains nine items with two dimensions (ie, overall memory function and time comparison [OMTC], and daily activity ability [DAA]). Sleep duration was assessed by asking the participants, “In the past month, how long did you actually sleep at night?”. [BMC Psychiatry 2022;22:147]

Based on earlier epidemiological data in Guangdong, the participants were categorized into three groups, including short (<6 hours; 35.3 percent), normative (reference group; 6 to 8 hours; 51.7 percent) and long sleepers (≥8 hours; 12.9 percent).

Results showed significant U-shape associations between sleep duration and overall SCQ-Q9 score (effective degree of freedom [EDF], 3.842; p<0.001) and OMTC score (EDF, 4.471; p<0.001) in the age- and gender-adjusted generalized additive model (GAM). After further adjusting for other sociodemographic characteristics (ie, residence, education, cohabitation status and monthly income), lifestyle variables (ie, smoking, alcohol assumption, tea-drinking habit, napping habit and exercise frequency) and common chronic disease status (ie, hypertension, hyperlipidaemia and diabetes), the U-shaped associations between sleep duration and overall SCQ-Q9 score (EDF, 3.575; p=0.004) and OMTC score (EDF, 4.478; p=0.010) persisted.

“[Notably,] those participants who slept for 8 hours had the lowest overall SCD-Q9 score and OMTC score,” highlighted the researchers.

However, it should be noted that the association between sleep duration and SCCs was no longer statistically significant after adjusting for depression and anxiety symptoms (sleep duration and overall SCD-Q9 score: EDF, 3.689; p=0.158) (sleep duration and OMTC score: EDF, 4.464; p=0.136). “[This suggests that] anxiety and depression symptoms might [exert a] mediating effect or moderating effect in the association between sleep duration and SCCs,” they noted.

The association between DAA and sleep duration also appeared to be U-shaped (EDF, 2.314; p<0.001). However, the U-shaped relationship weakened after further adjusting for other sociodemographic characteristics, lifestyle factors and common chronic disease status (EDF, 2.080; p=0.010). “Those results could be explained by the observation that when there were complaints about memory, people with subjective cognitive decline may still have normal ability of daily living,” they elaborated.

“This is the first paper to demonstrate a U-shaped association between sleep duration and SCCs, as well as its two dimensions. This study filled the gap in the correlation between sleep duration and SCCs,” they continued. “These results could provide more information about the profile of SCCs in Chinese elderly.”