Positive affect and sleep: A systematic review

Summary

A sizeable literature has implicated sleep in the phenomenological experience of various mood disorders, vulnerability to psychopathology, and overall poor psychological functioning. By contrast, positive affective states (e.g., joy, happiness, vigor, positive mood) that may contribute to sleep have been understudied. This systematic review integrates findings from cross-sectional, longitudinal, ambulatory, and experimental studies that investigate the association between positive affect and sleep. A comprehensive search for all available research on the topic was performed in three electronic bibliographic databases (PubMed, PsycINFO, CINAHL). Two independent reviewers extracted data on study characteristics and quality. From 10,853 retrieved articles, 44 fulfilled inclusion criteria and formed the base of the review. The majority of studies (68.2%, n = 30) were classified as weak or having high risk of bias. In general, the pattern of findings suggests that aggregate or trait measures provide the most consistent evidence of an association between positive affect and sleep in healthy populations. More limited empirical data exist on the association between positive affect and sleep in clinical populations. We conclude that more rigorous and theoretically informed research is needed before firm conclusions can be drawn about the possible beneficial impact of positive affect on sleep outcomes.

Introduction

Extensive research has documented the importance of sleep for promoting restorative processes and protecting against impairments in a range of neurobehavioral functions, including emotion regulation, immune control, and memory consolidation [1], [2], ∗[3], [4]. Moreover, deficits in fundamental aspects of sleep, including sleep efficiency (i.e., initiating and maintaining sleep) and sleep quality (i.e., feeling rested and restored upon waking), can have profound health effects that contribute to increased risks for adult morbidity and all-cause mortality [5], [6], [7], [8]. Given the significant role of sleep in psychiatric and health morbidities, it is important to advance understanding of the key factors that contribute to individual differences in sleep quality.

There is growing interest in associations between positive affect (PA) and health outcomes ∗[9], [10], [11], [12]. Positive affect can be defined as a state of pleasurable engagement with the environment that elicits feelings, such as happiness, joy, excitement, enthusiasm, and contentment [13]. Encompassing both enduring moods (e.g., affective traits) as well as short-term emotions (e.g., dynamic states), PA has been found to be robustly associated with lower morbidity and reduced mortality in both healthy and clinical populations [13], [14], [15], [16]. Moreover, growing evidence suggests that PA is an important factor affecting individuals' overall sleep. Adults who report high levels of PA exhibit improved sleep patterns ∗[17], [18]. In contrast, those who experience difficulties regulating PA report greater sleep disturbances [19].

How might PA influence sleep? Pressman and Cohen [9] propose two general mechanisms—main effects and stress-buffering—by which PA can promote health. In the main-effect model, PA impacts behaviors relevant to health in general, irrespective of its effects on stress responses. For example, individuals with high trait PA may be more likely to engage in restorative health practices such getting sufficient and restful sleep [17]. By contrast, in the stress-buffering model, PA may act to reduce negative appraisals of stress and facilitate adaptive coping. Individuals with high trait PA may cope more effectively with stressors and, therefore, may not experience the adverse health consequences of stressor exposure vis-à-vis poor sleep quality [20]. Studies also suggest that PA and sleep are associated through a bidirectional relationship ∗[17], ∗[19]. For example, reciprocal inverse relations between vigor and insomnia were reported in a longitudinal study of working adults [21]. Regardless of whether PA influences sleep through direct, stress-buffering, or bidirectional effects, no systematic review has yet investigated the association between PA and sleep. Moreover, while a number of reviews have focused on links between general emotion and sleep ∗[3], ∗[22], results to date have raised important methodological questions, such as the directionality of emotion effects, the equivalence of standard subjective and objective measures of sleep, the contribution of PA to both resilience-enhancing and vulnerability-inducing sleep outcomes, and the extent to which associations between PA and sleep are independent of negative affect (NA).