the impact of sleep on dealing with daily stressors—a need for controlled laboratory evidence....
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194 Stress and Health 26: 194–197 (2010) © 2010 John Wiley & Sons, Ltd.
COMMENTARY
The Impact of Sleep on Dealing with Daily Stressors—A Need for Controlled Laboratory Evidence
Commentary on Barber, Munz, Bagsby & Powell (2009) ‘Sleep Consistency and Suffi ciency: Are Both Necessary for Less Psychological Strain?’Clare Anderson*†
Division of Sleep Medicine, Brigham and Women’s Hospital, and Harvard Medical School, Boston, MA, USA
*Correspondence
Clare Anderson, Division of Sleep Medicine, Brigham and Women’s Hospital and Harvard Medical School, 221, Longwood Avenue,
Boston, MA 02115, USA†Email: [email protected]
Published online 22 January 2010 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/smi.1301
Issues concerning health and well-being are known to
have a major impact on the academic performance and
quality of life of university students, and yet many
undergraduates relinquish nightly sleep for other
activities with little awareness of the consequences.
While many adults report inadequate or poor sleep
(Groeger, Zijlstra, & Dijk, 2004), the extent of the
problem is particularly notable and appears to be
growing in college students. Seventy-one percent of
Under graduate college students reported sleep com-
plaints in 2000, compared with 53% in 1988 and
24% in 1978 (Hicks, Fernandez, & Pellegrini, 2001a;
Voelker, 2004). Over the last three decades, mean
sleep duration has shortened by more than 1 h to 6.75 h
(Hicks, Fernandez, & Pellegrini, 2001b), with 35% of
college students staying up until 3 am at least once
per week (Lund, Reider, Whiting & Prichard, 2009).
The underlying cause of these altered sleep habits
is multi-faceted, including increased social, academic
and employment demands, as well as maturational
changes in the biological processes that regulate the
sleep—wake cycle (Carskadon, Acebo, & Jenni,
2004). According to the American College Health Asso-
ciation’s (ACHA, 2009) National College Health
Assessment (NCHA), students consistently identify
sleep and stress as major factors in impeding their aca-
demic performance. As such, the question posed by
Barber and colleagues (‘Sleep consistency and suffi -
ciency: are both necessary for less psychological strain?’)
addresses a fundamental and timely issue for college
students.
The reported study (Barber, Munz, Bagsby, & Powell,
2009) examines a group of eighty-eight university
undergraduates categorized according to whether they
obtain suffi cient or insuffi cient sleep, dependent on
whether they sleep more or less than 7 h per night, and
whether the timing of this sleep is consistent or incon-
sistent over fi ve consecutive weekdays. Early week
(Monday to Thursday) sleep is used to identify late
week (Friday) perceived strain, and consistent with
their hypotheses, the authors conclude that consistent-
suffi cient sleepers reported less late-week strain than
other groups. The study frames the perceived psycho-
logical benefi ts of sleep in terms of a self-regulatory
strength model (Baumeister, Bratslavsky, Muraven, &
Tice, 1998), which conceptualizes the benefi ts of suffi -
cient sleep as resource replenishment, and consistent
sleep as a resource enhancer. Although the results pre-
sented by Barber et al. are consistent with previous
empirical evidence demonstrating both quality and
quantity of sleep are important in the regulation of
stress and strain (Pilcher, Ginter, & Sadowsky, 1997;
Pilcher & Ott, 1998), the interpretation of causality is
beyond the scope of this study.
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Stress and Health 26: 194–197 (2010) © 2010 John Wiley & Sons, Ltd. 195
C. Anderson Impact of Sleep
The causal nexus between stress and problem sleep is
well known: stress leads to sleeplessness, and sleepless-
ness leads to stress. Given the study design employed
by Barber et al., as with many naturalistic studies exam-
ining this issue, the causal relationship between sleep
parameters and perceived stress/strain is unknown.
Although much is known about the impact of stress on
sleep (c.f. Kim & Dimsdale, 2007), well-controlled
empirical evidence is now emerging which addresses
the dependency of stress regulation on adequate,
quality sleep (c.f. Van Reeth et al., 2000). Extended
wake has recently been shown to affect hippocampal
function (Vecsey et al., 2009), and weaken functional
connectivity between the amgydala and medial pre-
frontal cortex (Yoo, Gujar, Hu, Jolesz, & Walker, 2007),
which are key structures in the behavioural and physi-
ological responses to stress (McEwan, 2006). Studies in
both humans and rodents have shown that sleep
deprivation and restriction may act on stress systems
(i.e. the autonomic sympatho-adrenal system and the
HPA axis), while also affecting the reactivity of these
systems to other stressors and challenges (Meerlo,
Sgoifo, & Suchecki, 2008; Van Reeth et al., 2000). These
physiological changes in the stress response caused by
sleep loss may explain how insuffi cient sleep exacer-
bates negative moods (Wolfson & Carskadon 1998),
decreases the ability to control or modify emotional
responses (Dahl, 1999), and alters perceived ratings of
strain as seen here (Barber et al., 2009). The resource
replenishment model of sleep mediating self-regulatory
behaviour may therefore be a useful conceptualization
of these issues, and may have an underlying physiologi-
cal basis.
Inconsistent sleep leads to poor quality sleep, pri-
marily because of sleeping at varying circadian phases
(Czeisler, Weitzman, Moore-Ede, Zimmerman, &
Knauer, 1980). With respect to mood, stress or strain,
sleep quality is often more important than sleep quan-
tity (e.g. Pilcher et al., 1997; Pilcher & Ott, 1998).
Barber and colleagues describe the signifi cance of early-
week sleep consistency for improving late-week strain
via the resource-enhancement approach: building self-
regulatory capacity over time by exerting self-control
over the timing of sleep. Although the authors discount
circadian rhythm disruption as an explanation for their
fi ndings, simply controlling for clock time does not
control for the contribution of circadian factors on the
effects of inconsistent sleep. The endogenous clock is
highly sensitive to environmental light (Zeitzer, Dijk,
Kronauer, Brown, & Czeisler, 2000). As altering the
timing of sleep alters the light–dark exposure (Wright,
Gronfi er, Duffy, & Czeisler, 2005), those sleeping at
irregular times are likely to be exposed to light at
varying circadian times, resulting in phase advances
and/or phase delays of the clock (Duffy & Czeisler,
2009). As such, those students who have irregular sleep
hours may remain in a state similar to ‘jet lag’. Postpon-
ing the timing of sleep by only 2 h induces feelings of
depression (Cardinali, 2000), reduced affability and
increased diffi culty in concentration (Taub, 1978). Fur-
thermore, recent research in rodents suggests exposure
to unnatural light may induce signifi cant changes in
affect, with an increase in depressive symptomology
(Fonken et al., 2009). However, the extent to which this
is replicable in humans in currently unknown.
A major contributory factor overlooked by Barber
et al. concerns individual differences in diurnal prefer-
ence. Morningness and Eveningness is related to inter-
individual differences in circadian phase and indicates
an individual’s preferred timing of behaviours. The bio-
logical rhythms of individuals are shifted to accommo-
date fi xed social and/or academic constraints. The four
groups presented in Barber et al.’s study (Suffi cient/
Insuffi cient and Consistent/Inconsistent) are catego-
rized based on self-selected sleeping habits. As such,
those individuals who fall into the consistent-suffi cient
sleep group are likely to be more morning type, and
those in the inconsistent-insuffi cient group are likely to
be more evening type—evening types typically have less
time in bed during the week and more irregular sleep/
wake habits (Taillard, Philip, & Bioulac, 1999). The
morning type individual typically wakes early feeling
refreshed, goes to bed early and consistently, and is
conscientious and emotionally stable. In contrast, the
evening type gets up with diffi culty, stays up late and is
less emotionally stable (c.f. Cavallera & Giudici, 2008).
Moreover, evening types report more psychological and
somatic disorders including greater levels of anxiety,
increased diffi culty in coping with environmental
and social demands (Macacci & Rocchetti, 1998), and
are more likely to report depressive symptoms
(Chelminski, Ferraro, Petros, & Plaud, 1999). From
a physiological perspective, evening types exhibit
increased stress reactivity during the afternoon/early
evening compared with morning types (Nebal et al.,
1996; Willis, O’Connor, & Smith, 2006), which coinci-
dentally or not, was when perceived strain ratings were
conducted in the current study. Interestingly, evening
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Impact of Sleep C. Anderson
196 Stress and Health 26: 194–197 (2010) © 2010 John Wiley & Sons, Ltd.
types do show diffi culty in self-regulation and demon-
strate little self-control (Digdon & Howell, 2008),
which may contribute to the erratic sleep schedules seen
in this cohort. In addition to the schedules kept by
evening type individuals, these chronotypes are also
more likely to consume caffeine (Cavallera & Guidici,
2008), which in turn will exacerbate problems with
sleep initiation/maintenance (Smith, 2005). Individual
differences in diurnal preference play a large role in the
stress/strain response mediated by sleep, and may have
been unintentionally captured in the study reported by
Barber et al.
In sum, Barber et al. contribute to a growing body
of evidence highlighting the impact of sleep quantity
and quality on perceived ratings of stress and strain
in university undergraduates. Although the self-
regulatory model of sleep may be used to conceptualize
these issues, especially resource replenishment, framing
the timing of sleep as exercising self-control to build
self-regulatory capacity is beyond the scope of the
study. Links between inconsistent sleep and perceived
strain may be mediated, in part, by differences in sleep
quality, underlying stress, exposure to light, diurnal
preference, personality factors and other inter individ-
ual differences. As such, future work examining the
benefi ts of exerting self-control on sleep practices
should be based on controlled, intervention studies.
Irrespective of the interpretation, Barber et al.’s fi nd-
ings of late week strain because of early week sleep
under naturalistic non-controlled conditions should
prompt further well-controlled research as anticipated
by the authors. Although there is an abundance of well-
controlled research studies that seek to understand the
effects of acute or chronic sleep loss on cognition, evi-
dence of sleep suffi ciency and consistency in the ability
to regulate emotion, stress and strain is lacking, despite
problems with sleep and emotion becoming more
endemic in modern society, among college students
and beyond.
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