Original articleGratitude influences sleep through the mechanism of pre-sleep cognitions
Introduction
Personality is an important predictor of sleep quality and quantity [1]. Most previous research has focused on which personality traits are related to impaired sleeping. Neuroticism has emerged as a robust predictor of sleep quality, with people who are dispositionally stressed, depressed, anxious, and angry being shown to suffer from poor sleep [2], [3], [4], [5], [6], [7]. This research has been influential both in developing models of the etiology of insomnia and in developing psychological treatments of sleep disorders [1]. However, the positive psychology movement has emphasized the importance of studying positive aspects of life in addition to the more traditional psychological focus on psychopathology [8], [9], [10]. Positive well-being involves more than the absence of mental illness [11], and positive traits have been shown to explain additional outcomes in health and well-being variables after controlling for neuroticism [12], [13], [14]. Recently, positive psychological well-being has been linked to improved quality of sleep [15]. It is not clear, however, whether positive psychological traits can explain sleep quality above the effect of other more traditionally studied personality traits, including the negative traits represented within the construct of neuroticism. Additionally, there is no indication of the mechanisms which explain why positive psychological traits are related to sleep. This study examines these questions with regard to the specific positive psychological trait of gratitude.
Gratitude is perhaps the quintessential positive psychology trait, involving a life orientation towards the positive in the world [16]. In addition to feeling more grateful affect [17], grateful people focus on the positive in their environment and have greater appreciation of their possessions and social relationships [18]. As a trait, gratitude is related to positive coping [19], social functioning [20], and has a unique and causal effect on positive well-being and social relationships [14], [21], [22]. The aim is to investigate whether individual differences in gratitude are related to sleep, after controlling for neuroticism and other personality traits, and to test for the mediational mechanisms underling this relationship.
Only one previous study has indicated that trait gratitude may be related to sleep, and no previous study has suggested mechanisms which may underlie this relationship. Patients with neuromuscular disorders listed three things for which they were grateful each night for 21 nights. Subsequently, their physical and mental well-being was compared with a control group which simply completed outcome measures [21]. The gratitude group self-reported increased hours of sleep and an improved sense of refreshment upon waking. Gratitude was selected as the focus of this study due to this indication that trait gratitude may be related to sleep, and due to the centrality of gratitude as a positive trait [23]. The current study will extend this work by testing which aspects of sleep are related to gratitude, whether this relationship is independent of the effects of other personality traits, and by investigating the mediational mechanisms that may explain the relationship between gratitude and sleep quality.
It is suggested that pre-sleep cognitions may underlie the relationship between gratitude and sleep quality. Pre-sleep cognitions are the thoughts that people have just before sleep. A large literature has linked pre-sleep cognitions with sleep quality [24], [25], [26], [27], [28], [29], and experimental evidence has suggested that increased pre-sleep cognitions cause impaired sleep [30], [31], [32], [33]. Negative pre-sleep cognitions have attracted particular empirical attention, as precursors of impaired sleep. More recently, positive pre-sleep cognitions are beginning to be studied [24], and there is indication that positive cognitions are related to good sleep quality [34], [35]. As there is evidence that gratitude causes a variety of positive cognitions, including life evaluations [21], perceptions of social support [22] and social situations [20], it may be that gratitude is one determinant of pre-sleep cognitions.
Specifically, we suggest that grateful people will have less negative pre-sleep cognitions (which impair sleep) and more positive pre-sleep cognitions (which promote sleep). This is the first empirical study to link trait gratitude to sleep or to suggest mechanisms explaining why this relationship may occur. With gratitude interventions increasingly being promoted in clinical settings [36], [37], [38], establishing the mechanisms linking gratitude and sleep will indicate the potential of gratitude interventions for treatment of insomnia. This is also the first study to investigate the potential for positive traits to increase our understanding of sleep above the effects of neuroticism. More generally, this is the first study to investigate pre-sleep cognitions as a mechanism linking any personality trait to sleep.
Section snippets
Participants and procedure
Participants were 401 (186 male, 215 female) people recruited from the local community by one of two research assistants. Ages ranged from 18 to 68 years (mean=24.89, S.D.=9.02), with 80.3% aged under 30, and 90.1% aged under 40. Participants were either recruited from administrative workers in the head office of a large multinational company in London (n=200) or approached at a large chain of coffee shops in the South West of England, a community center in East Midlands, or a local Arts Center
Results
The total PSQI score was approximately normally distributed. The mean total PSQI score was 5.44 (S.D.=2.57), slightly higher than representative population surveys (mean=4.55, S.D.=3.71, t [1390]=4.45, d=.28) [44]. At the standard cut-off point of 5, 161 people (40%) could be classified as poor sleepers (compared to 32.1% in population surveys).
In the total sample, higher scores on the GQ-6 were positively associated with superior sleep quality (indicated by lower scores on the PSQI), with
Discussion
Gratitude was uniquely related to total sleep quality, subjective sleep quality, sleep latency, sleep duration, and daytime dysfunction, after controlling for the effects of the Big Five and social desirability. The results of the current study also provide evidence that pre-sleep cognitions mediate the relationship between trait gratitude and sleep quality. When falling asleep, grateful people are less likely to think negative and worrying thoughts, and more likely to think positive thoughts.
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These authors made equal scientific contributions.