The Effects of Psychosocial Factors and Biomarkers on the Association between Sleep and Life Satisfaction Among Middle-aged American Adults

Background: Sleep disorders are a highly prevalent public health issue, which affect up to 70 million individuals in the United States. Poor sleep quality may lead to mental and physical health issues, which relates to the lower level of life satisfaction. Although the associations among sleep quality, psychosocial factors, biomarkers and life satisfaction were shown in previous studies, the effects of psychosocial factors and biomarkers on the relationship of sleep quality with life satisfaction among middle-aged American adults were not completely understood. This study aims to comprehensively investigate the roles of psychosocial factors (depressive symptoms and perceived stress) and biomarkers (fasting blood glucose and C-reactive protein [CRP]) in the association of sleep quality with life satisfaction.

Methods: This integrative doctoral research using data from the Midlife in the United States (MIDUS) Study conducted a half-longitudinal study and applied serial multiple mediation models. MIDUS 2, MIDUS Biomarker project and MIDUS 3 were invoked. We used the statistical software package SAS 9.4 to produce descriptive statistics and applied hierarchical regression models to explore the associations among sleep quality, psychosocial factors, biomarkers and life satisfaction. Serial mediation models (PROCESS model 6, SAS programs developed by Hayes 2013) were applied to explore the impacts of psychosocial factors and biomarkers on the relationship of sleep quality with life satisfaction.

Results: Our final research involved a total of 945 participants. Serial mediation analyses showed that the relationship between sleep quality and life satisfaction was significantly mediated by both psychosocial factors (perceived stress and depressive symptoms) and biomarkers (CRP and fasting blood glucose), while controlling for demographic variables and life satisfaction at baseline. The findings from the study of psychosocial factors revealed that the direct effect of sleep quality on life satisfaction was significant (coefficient β = -0.0253, 95%CI =-0.0464 – -0.0042, P=0.0189). The total indirect effects of sleep quality on life satisfaction through perceived stress, depressive symptoms and the combination of perceived stress and depressive symptoms accounted for 45.5% of the overall model. The findings from the study of biomarkers revealed that the direct effect of sleep quality on life satisfaction was statistically significant (coefficient β = -0.0346, 95%CI: -0.053, -0.0162). The total indirect effects of sleep quality on life satisfaction through CRP and the combination of CRP and fasting blood glucose accounted for 5.7% of the overall model.

Conclusion: Both psychosocial factors (perceived stress and depressive symptoms) and the combination of biomarkers (fasting blood glucose and CRP) mediate the relationship of sleep quality with life satisfaction. However, compared to biomarkers (fasting blood glucose and CRP), psychosocial factors, including depressive symptoms and perceived stress, play more important mediating roles in the relationship of sleep quality with life satisfaction. The findings from our projects yield implications for clinical management to improve sleep quality and prevent perceived stress and depression, which contributes to improving the level of life satisfaction. Further cohort studies with more waves are needed to verify our results.