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Gratitude influences sleep through the mechanism of pre-sleep cognitions
Alex M. Wood
a,
⁎, Stephen Joseph
b
, Joanna Lloyd
c,1
, Samuel Atkins
c,1
a
School of Psychology, University of Manchester, Manchester, England, UK
b
University of Nottingham, Nottingham, UK
c
University of Warwick, Warwick, UK
Received 7 May 2008; received in revised form 4 August 2008; accepted 2 September 2008
Abstract
Objectives: To test whether individual differences in gratitude
are related to sleep after controlling for neuroticism and other
traits. To test whether pre-sleep cognitions are the mechanism
underlying this relationship. Method: A cross-sectional ques-
tionnaire study was conducted with a large (186 males, 215
females) community sample (ages=18–68 years, mean=24.89, S.
D.=9.02), including 161 people (40%) scoring above 5 on the
Pittsburgh Sleep Quality Index, indicating clinically impaired
sleep. Measures included gratitude, the Pittsburgh Sleep Quality
Index (PSQI), self-statement test of pre-sleep cognitions, the Mini-
IPIP scales of Big Five personality traits, and the Social
Desirability Scale. Results: Gratitude predicted greater subjective
sleep quality and sleep duration, and less sleep latency and
daytime dysfunction. The relationship between gratitude and each
of the sleep variables was mediated by more positive pre-sleep
cognitions and less negative pre-sleep cognitions. All of the
results were independent of the effect of the Big Five personality
traits (including neuroticism) and social desirability. Conclusion:
This is the first study to show that a positive trait is related to
good sleep quality above the effect of other personality traits, and
to test whether pre-sleep cognitions are the mechanism underlying
the relationship between any personality trait and sleep. The study
is also the first to show that trait gratitude is related to sleep and to
explain why this occurs, suggesting future directions for research,
and novel clinical implications.
© 2009 Elsevier Inc. All rights reserved.
Keywords: Gratitude; Personality; Sleep; Pre-sleep cognitions; Positive psychology
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. Neuroti-
cism 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 [2–7]. 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 [8–10].
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 [12–14]. 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 psycho-
logy trait, involving a life orientation towards the positive in
the world [16]. In addition to feeling more grateful affect
Journal of Psychosomatic Research 66 (2009) 43–48
⁎Corresponding author. School of Psychology, University of Manchester,
Manchester, England, UK. Tel.: +44 7790 816407.
E-mail address: alex.wood@manchester.ac.uk (A.M. Wood).
1
These authors made equal scientific contributions.
0022-3999/09/$ –see front matter © 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.jpsychores.2008.09.002
[17], grateful people focus on the positive in their
environment and have greater appreciation of their posses-
sions 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 relation-
ship. 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 investigat-
ing 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 [24–29], and experimental evidence has
suggested that increased pre-sleep cognitions cause
impaired sleep [30–33]. 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 [36–38],establishingthe
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.
Method
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 adminis-
trative 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 in the East
Midlands (n=201). Participation was voluntary and without
payment, and 75% of those approached agreed to participate.
Prior to completing the questionnaire the participants read a
sheet providing details of the study and ethical information,
and participants signed a declaration of informed consent.
All measures were completed in English with pencil and
paper. Prior to data collection the study was approved
according to the institutional review procedures of the
University of Warwick, and the research followed the ethical
guidelines of the American Psychological Association.
Measures
Gratitude was measured with the GQ-6 [13]. Six items
assess the frequency and intensity with which grateful affect
is experienced, and the range of events which elicit gratitude
[e.g., “I have so much in life to feel thankful for”(Item 1), “I
am grateful to a wide variety of people”(Item 4), and “When
I look at the world, I don't see much to be grateful for”(Item
3, reverse coded)]. Items are rated on a 1 (strongly disagree)
to 7 (strongly agree) scale. The GQ6 has a robust one-factor
structure, convergent validity with peer reports [13], and
high test–retest reliability [22].
Pre-sleep cognitions were measured with the self-
statement test [24]. Participants rate how frequently they
experience 60 different thoughts, in general, when trying to
initially fall asleep or get back to sleep. Items are rated on a 0
(never or hardly ever)to4(very often) scale. Items were
developed on the basis of a qualitative study of the thoughts
people experience whilst trying to fall asleep and include
both positive (e.g., “enjoyable things I did during the last few
days”) and negative pre-sleep cognitions (e.g., “bad things
happening in the world”). The self-statement test discrimi-
nates between insomniac and normal populations (known
group validity) and positive and negative thoughts load on
different factors [24].
Sleep was measured with the Pittsburgh Sleep Quality
Index (PSQI) [39]. Referring to the past month, 19
questions ask about sleep quantity (e.g., “when have you
44 A.M. Wood et al. / Journal of Psychosomatic Research 66 (2009) 43–48
usually gone to bed at nights?”;“when have you usually
gotten up in the morning?”;“how many actual hours of
sleep did you get at night?”) and sleep quality (e.g., “how
would you rate your sleep quality overall?”). Responses are
made in a variety of formats; all responses are recoded on a
0–3 scale based on the ranges specified by the scale
development paper (the recoding also has the effect of
removing the effect of extreme outliers). A total sleep score
is formed, in addition to seven subscales representing sub-
jective sleep quality,sleep latency (how long it takes to get
asleep), sleep duration,sleep efficiency (hours spent asleep
divided by number of hours in bed), sleep disturbances,use
of sleep medicine, and daytime dysfunction (e.g., difficulty
staying awake during the day). The total sleep score and all
subscales are scored so that higher scores indicate more
impaired sleep and higher sleep dysfunction. The PSQI can
be used as a continuous measure of the continuum of
impaired sleep. Alternatively, using a total score N5 has
been shown to discriminate between groups of healthy
volunteers and groups referred to sleep disorder clinics by
physicians for sleep disorders (sensitivity and specificity of
N85%) [39]. The scale is one of the most widely used
measures of sleep in clinical research and practice.
The Big Five personality traits were measured with the
Mini-IPIP scales [40]. The personality factors of neuroti-
cism, extraversion, agreeableness, conscientiousness, and
openness are assessed with 20 items (four per factor,
including a mixture of positively and negatively worded
items). These five traits have been shown to represent all
of personality at the broadest level of abstraction [41,42].
The Mini-IPIP shows very good test–retest reliability,
convergent, discriminant, and criterion-related validity,
which is comparable to the NEO and other measures of
the Big Five [40].
Social desirability was measured with the Social Desir-
ability Scale-17 [43]. Sixteen items (seven reverse coded)
provide statements with which most people would like to
agree but are probably unable to do so truthfully (e.g., ‘‘I
always accept other's opinions, even when they don't agree
with my own”). (The measure originally had 17 items, but
one item was deleted in the scale validation process; we used
the revised 16-item version as recommended by the authors
[43].) Participants respond “true”or “false”to each item, and
higher scores represent socially desirable responding. The
measure was developed due to concerns that the items in
older measures were no longer socially desirable. The
measure shows sensitivity to socially desirable situations
(e.g., job applications), good convergent validity, and all
items have recently been rated as socially desirable [43].
Results
The total PSQI score was approximately normally dis-
tributed. 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 gratitude negatively
correlating with six measures of impaired sleep quality:
total sleep quality (r=−.29, Pb.001), subjective sleep
quality (r=−.25, Pb.001), sleep latency (r=−.20,
Pb.001), sleep duration (r=−.14, Pb.01), habitual sleep
efficiency (r=−.11, Pb.05), and daytime dysfunction (r=
−.27, Pb.001). Gratitude was also positively correlated
with positive pre-sleep cognitions (r=.21, Pb.001) and
negatively correlated with negative pre-sleep cognitions (r=
−.11, Pb.001). A series of multiple regressions were
conducted to test whether the relationship between
gratitude and sleep was mediated by positive and negative
pre-sleep cognitions, using Baron and Kenny's [45] three
mediational steps and the Sobel test [46]. As gratitude was
positively correlated with extraversion, agreeableness, and
conscientiousness, and negatively correlated with neuroti-
cism (rranged from |.23| to |.35|, all Pb.001), the Big Five
traits and social desirability were also included as predictor
variables in each of the regressions in order to control for
the effects of these traits at each stage of the analysis.
Baron and Kenny's [45] first step requires the predictor to
be related to the outcome. With the effects of the Big Five
and social desirability controlled, gratitude still significantly
predicted total sleep quality (β=−.24, Pb.001), subjective
sleep quality (β=−.25, Pb.001), sleep latency (β=−.17,
P=.002), sleep duration (β=−.15, P=.006), and daytime
dysfunction (β=−.16, P=.003). Gratitude was not uniquely
related to sleep efficiency (β=−.08 P=.144), failing Baron
and Kenny's first step; this variable was not included in any
further analysis.
The second step was conducted separately for each of the
five sleep variables with which gratitude showed a unique
relationship (these are presented as path diagrams in Fig. 1,
where each of the path values shown is independent of the
effects of social desirability and the Big Five). This step
requires the mediators (pre-sleep cognitions) to be signifi-
cantly related to the outcome (the sleep measure) after
controlling for the predictor (gratitude). As shown in Fig. 1,
this step was met in each case.
In the third step, mediation is demonstrated if controlling
for the mediator significantly reduces the relationship
between the predictor (gratitude) and the outcome (sleep)
relative to the zero-order correlation. Sobel's ztests whether
the decrease in βis statistically significant and is mathema-
tically equivalent to testing the significance of the mediated
pathway [46].Fig. 1 shows Sobel's zfor each mediated
pathway and demonstrates that either positive or negative
pre-sleep cognitions significantly mediated the relationship
between gratitude and each of the five measures of sleep
(fulfilling the third step). Positive pre-sleep cognitions
45A.M. Wood et al. / Journal of Psychosomatic Research 66 (2009) 43–48
mediated the relationship between gratitude and subjective
sleep quality, sleep duration, sleep latency, and sleep
efficiency. Negative pre-sleep cognitions mediated the
relationship between gratitude and subjective sleep quality,
sleep latency, sleep efficiency, and daytime dysfunction.
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. It appears that negative pre-sleep
cognitions impair sleep, and gratitude reduces the likelihood
of such thoughts, protecting sleep quality. Equally, it appears
that positive pre-sleep cognitions have a positive effect on
sleep, and that gratitude facilitates these thoughts, leading to
superior sleep quality.
It is notable that gratitude was related to sleep and pre-
sleep cognitions after removing the effects of the Big Five
personality traits. This suggests that gratitude is not simply
linked to sleep due to the third variable effects of broad
personality traits or dispositional affect. Increasingly, there is
Fig. 1. Tests of mediation between gratitude and five sleep measures, with standardized β's and Sobel's z. All values are after covarying the effects of social
desirability and the Big Five. ⁎⁎⁎Pb.001, ⁎⁎Pb.01, ⁎Pb.05.
46 A.M. Wood et al. / Journal of Psychosomatic Research 66 (2009) 43–48
evidence that gratitude can predict well-being outcomes
above the effects of other personality traits [13,17,20,22],
including social desirability [18], coping [19], and the 30
facets of the Big Five [14]. The present results suggest that
gratitude may also uniquely be related to sleep, at least above
the broad effects of the Big Five. As positive and negative
affect are respectively represented in the Big Five traits of
extroversion and neuroticism [47], the results suggest that
the relationship between gratitude and sleep is not simply a
reflection of the relationships between gratitude and positive
affect (or “happiness”) or negative functioning (e.g., stress,
depression, anxiety, and negative affect). The Big Five traits
can, however, achieve broad coverage of the personality
domain at the expense of specificity [48]. Future research
should measure positive and negative affect specifically to
test whether the mechanism linking gratitude and sleep is
purely cognitive (as indicated by the current demonstration
of mediation via pre-sleep cognitions) or whether daily affect
forms a second mediational pathway.
More research is needed into whether other positive
traits can explain sleep and sleep disorder, in order to
develop more complete models of sleep functioning.
Research is also needed into whether increasing positive
traits improves sleep. Emmons et al. show that therapeu-
tically increasing gratitude can increase sleep quality [21].
Further work is needed to explore the efficacy of this
approach in insomnia patients to test whether including a
focus on gratitude can improve existing sleep therapies and
whether pre-sleep cognitions are the mechanism through
which the therapy operates.
The study had some limitations, including the reliance on
self-report measures. This was partially mitigated by the use
of the PSQI measure of sleep (which discriminates between
groups of healthy people and physician-referred insomniacs
with sensitivity and specificity of N85%) [39] and through
showing that the results were not confounded with socially
desirable responding. Self-reports of sleep are also important
in themselves, given that most people self-refer to sleep
clinics. There is also evidence that mood and objective daily
performance is more strongly related to the self-report of
sleep quality than to sleep quality measured through
neuropsychological assessment [49]. However, further
research is needed into whether gratitude and other positive
traits are related to objective sleep assessment measured by
EEG (actual sleep measured through brain waves) or
actigraphy (actual sleep measured via wrist movements).
The current study also used a community sample, rather than
a sample of people clinically diagnosed with insomnia. The
community sample had the advantage of a wide range of
both personality and sleep quality, whereas a slanted clinical
sample would probably have exhibited range restrictions,
producing biased statistical analysis. However, future
research is needed into whether the findings extend to
clinical samples, perhaps using the experimental methodo-
logy discussed above. Finally, as the study was cross-
sectional it is not possible to demonstrate causality, and the
mediational analysis relies on the variables being arranged in
the correct order, which is normally inferred on the basis of
previous research [45]. However, given that gratitude has
been previously shown to cause better sleep [13], pre-sleep
cognitions have been shown to causally influence sleep [30–
33], and gratitude causally influences cognitions [20–22],it
seems likely the causal chain was correctly arranged in the
mediational analysis.
The results present the first indication that individual
differences in gratitude are related to sleep quality and
suggest that this is due to the mechanism of pre-sleep
cognitions. More research is needed into the role of
gratitude and other positive traits in relation to quality of
sleep in both healthy and clinical populations. Such a
positive psychology approach to sleep could potentially
provide better understanding of the etiology of sleep
disorders, explanation of positive sleep quality, and lead to
new therapies to treat sleep disorder and promote optimal
sleeping amongst the general population.
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