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: canderson22@rics.bwh.harvard.edu

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.

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

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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