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7 Arousal States, Symptoms, Behaviour, Sleep … 189
upon pain sensitivity [88, 96], suggesting that a bidirectional relationship
does exist between impaired sleep and pain.
Paradoxically, pain medications (e.g. morphine) are also reported to
impair sleep quality [97, 98], potentially leading to a difficulty in dis-
tinguishing between pain-induced and pain medication-induced sleep
deficits. Nevertheless, the aforementioned studies suggest that the experi-
ence ofpain, especially at night, tendsto impair sleep,including adifficulty
in falling asleep and poor sleep quality. Furthermore, in the case that a
person’s slow-wave sleep is compromised, then this may worsen the per-
ception of pain; if an opioid pain medication is used, this may also tend
to impair sleep.
Chronic pain isalso highly comorbid with anxiety and depressed mood.
Two large population-based surveys have examined comorbidity between
chronic pain and DSM-IV mood and anxiety disorders. Demyttenaere
and colleagues [99] detected a pooled OR of 2.3 at 21 months, between
comorbid neck and/or back pain and major depressive disorder, relative to
neck/back pain alone and the pooled OR for any anxiety disorder was 2.2,
even after adjusting for age, sex, race/ethnicity and education, in a cross-
national survey of 85,088community-dwelling adults across 18countries.
Similarly, Von Korff and colleagues [100] found that the 12-month co-
prevalence estimates for comorbid chronic pain and any mood disorder
was 17.5%; with major depression being the most common comorbid
mood disorder. Specifically, the pooled OR for the major depressive dis-
order was 2.5, and it is was 2.3 for any anxiety disorder, in a sample of
5692 community-dwelling US residents. Thus, it is evident that people
with chronic pain have at least twice the risk of developing an anxiety
or depressive disorder, even in the non-clinical setting; in turn, negative
affect may contribute to greater pain sensitivity, potentially via autonomic
hyper-reactivity, hypervigilance to the pain or another mechanism (e.g.
worry, avoidant behaviour) [101].
As might be expected, concurrence between pain and affective symp-
toms is even higher in chronic pain patients. For example, 82% of 728
patients who awaited treatment in the Canadian multi-disciplinary STOP-
PAIN project endorsed depression symptoms, and 56% of them reported
moderate-to-extremely severe depression and 34.6% reported suicidal
ideation [102]. Thus, anxiety and depressive disorders are common in
190 R. Brown and E. Thorsteinsson
chronic pain patients in the clinical setting. However, as morphine use
has been shown to be linked to stress/affective distress [103, 104], it may
not be the case that opiates can fully reduce a person’s pain-related distress.
Chronic pain is also frequently comorbid with overweight/obesity (e.g.
arthritis, low back pain) [105]. For example, in a US population study of
3637 adults, people classified as Class I obesity (BMI = 30–34.9) were
1.76 times more likely to report severe pain; people with Class II obesity
(BMI = 35–39.9) were 1.89 times more likely to report severe pain; and
those with Class III obesity (BMI ≥ 40) were 2.30 times more likely to
experience severe pain, relative to normal-weight and underweight indi-
viduals—with similar trends for moderate-to-severe pain [106]. However,
fewer longitudinal studies have been conducted, but they tend to show
that comorbidobesity is common inchronic pain conditionsand that pain
complaints are commonly reported by obese individuals. Several poten-
tial mechanisms have been advanced to explain the comorbidity including
mechanical/structural factors, chemical mediators, metabolic abnormal-
ities, depression, sleep and lifestyle, but the relationship is likely to be
multifactorial. Nonetheless, weight loss is an important aspect of pain
rehabilitation in obese chronic pain patients; that is, the pain is likely to
be reduced secondary to a person’s weight loss, although few studies have
confirmed the assertion [107–109].
However, few studies have explicitly examined pain in regard to BT,
other than in the cold pressor test (e.g. 1-minute immersion of hand
in ice water) [110], which is linked to an increase in heart rate, blood
pressure and SNS activation. Nevertheless, exposure to a cool ambient
environment (15 °C ± 0.5 °C) can decrease skin temperature, which
was linked to reduced thermal pain perception, relative to neutral (25 °C
± 0.5 °C) and warmer environments (35 °C ± 0.5 °C), in a study of
10 healthy volunteers, suggesting that human pain perception may be
dependent upon ambient temperature [111]. In contrast, fibromyalgia
syndrome (FM), which is characterised by widespread pain, is linked to
low BT, and it is exacerbated by cold and stress and temporarily relieved by
warmth. FM patients also often report non-restorative sleep, fatigue, cold
intolerance andneuroendocrine abnormalities,including an elevatedheart
rate, low metabolic rate and low skin temperature and vasoconstriction in
the skin overlying the tender joints. Additionally, there is an elevated risk
7 Arousal States, Symptoms, Behaviour, Sleep … 191
of obesity, insulin resistance and hyperlipidaemia in the patients [112].
Further complicating this picture, a dose-dependent relationship has been
observed between BT and opioid use; for example, a low morphine dose
increases BT in rats,whereas ahigher dosereduces BT [113]. However,due
to the paucity of relevant studies, it is unclear exactly how the experience
of chronic pain and its treatment is related to BT.
Nevertheless, as detailed above, autonomic arousal states (e.g. stress,
anxiety) and fatigue are known to be linked to an elevated BT, and as
described in Chapter 2, an elevated nocturnal BT can interfere with sleep
onset. Thus, it is possible that the thermogenic effects of stress, anxiety,
fatigue and possibly chronic pain, can at least partly explain the concur-
rence that exists between these symptoms and impaired sleep, possibly via
an increase in nocturnal BT. However, additionally, immune-mediated
pathways may be activated in response to thermogenic stimulation, as
detailed above, in regard to fatigue.
7.3 Exercise, S leep, Affective Distress,
Overweight/Obesity and Body
Temperature
Volitional physical activity is known to improve sleep [114] and well-being,
and it is linked to the experience of reduced stress and affective distress
(e.g. depression) [115]. Specifically, in healthy adults, as activity levels
increase, sleep onset latency tends to shorten and slow-wave sleep and
total sleep time increases [116]. Regular exercise (i.e. ≥ once/week) is
also correlated with fewer sleep complaints and less risk of developing a
sleep disorder [117]; adults who meet the US Centers for Disease Control
and Prevention (CDC) physical activity guidelines (i.e. 150 minutes of
moderate-intensity or 75 minutes of vigorous-intensity physical activity
or a combination of both) are less likely to experience daytime sleepiness,
relative to those who do not meet the recommended activity guidelines
[118].
Randomised controlledtrials (RCTs) have previously examined theben-
efits of physical activity on sleep in insomniacs. For example, a small
192 R. Brown and E. Thorsteinsson
16-week RCT incorporating aerobic exercise and sleep hygiene training
showed that aerobic exercise led to greater improvements in sleep onset
latency, sleep duration and sleep efficiency, relative to sleep hygiene train-
ing alone, in inactive older adults with insomnia, and the therapy resulted
in less daytime sleepiness and depression than at baseline [119]. A recent
Cochrane review has examined the effectiveness of physical activity pro-
grammes in treating insomnia in older adults [114], but only one trial
met the study’s inclusion criteria, which showed that physical activity
reduced sleep onset latency and improved sleep quality, sleep duration
and quality of life in the participants. However, few studies have exam-
ined physical activity and sleep in the sleep laboratory setting. As part
of the sleep heart health programme, the impact of vigorous exercise on
sleep-disordered breathing was evaluated in 275 participants [120], using
polysomnographic data and self-report questionnaires. At least 3 hours of
vigorous exercise/week was shown to be related to a significant reduction
in the riskof sleep-breathing symptoms, whereasa weaker relationship was
detected between moderate-intensity exercise and insomnia prevalence.
Taken together, the results suggest that even a few hours of regular
moderate-to-high intensity exercise each week can improve sleep in the
clinical and community setting. Nevertheless, the effectiveness of physical
activity in treating sleep problems is likely to be dependent upon the
specific type of sleep problem, severity of the sleep symptoms and the type
of physical activity engaged in [114]. In particular, low-intensity exercise
(e.g. tai chi) is not likely to improve a person’s sleep relative to higher
intensity activities [121].
However , the timing of the physical activity can be critical in determin-
ing whether it improves or hinders sleep. For example, vigorous exercise
undertaken late at night, especially just prior to bedtime, can lead to sub-
stantial pre-sleep autonomic arousal, which may potentially interfere with
sleep onset. For this reason, late-night exercise is considered to represent
poor sleep hygiene [122], whereas physical activity that is performed dur-
ing the day, especially if it is regular, is expected to result in good quality
sleep.
In sharp contrast, a sedentary lifestyle (e.g. physical inactivity, desk job,
watching TV) has been reported to adversely impact on health, including
sleep [123]. Physical inactivity is weakly correlated with high job strain
7 Arousal States, Symptoms, Behaviour, Sleep … 193
[124], and it is bidirectionally related to depression severity [125], sug-
gesting that physical inactivity tends to co-occur with symptoms of stress
and affective distress. On the other hand, physical activity has been shown
to be linked to better mental health; for example, in a large cross-sectional
study of 1,237,194 people aged 18 years or older (US CDC Behavioural
Risk Factors Surveillance System survey) [126] matched on BMI, demo-
graphics, self-reported physical health and prior depression diagnosis, the
people who exercised reported an average of 1.49 (43.2%) fewer days
of poor mental health over the past month, relative to those who did
not exercise. All exercise types were found to be related to lower mental
health burden, especially team sports, cycling and aerobic and gym exer-
cises, as were exercise durations of ≥45-minutes and frequencies of 3–5
times/week. Taken together, the results suggest that regular exercise can
assist a person to fall asleep faster, sleep for a longer time, and may protect
them from developing a sleep problem, whereas physical inactivity (or a
sedentary lifestyle) tends to interfere with sleep.
Several theories have been advanced to explain the way in which exer-
cise impacts on sleep and mood: it may lead to beneficial physiological
changes in homeostatic sleep regulation [127], including heat lossvia bod-
ily sweating; as a result, t his may lower BT [128], which assists in sleep
initiation, although the assertion requires testing in an empirical study.
Alternately, it is theorised that exercise can improve sleep indirectly via its
positive effects on mood and affective symptoms [129,130]. For example,
results from the British Birth Cohort Study (1958–2008) showed that less
physical activity predicted later worse depression symptoms at all ages,
whereas greater activity was related to a 19% reduced risk of later depres-
sion; depression in early adulthood predicted less physical activity in later
life. Taken together, the results indicate that the activity–depression rela-
tionship is bidirectional, likely reflecting that physical activity can prevent
the onset of mental health problems, whereas affective distress may hinder
a person’s later engagement with activity [125]. Similarly, a recent review
of the utility of physical activity programmes in improving mental health
showed that exercise significantly reduced depression symptoms [130],
and thus, it is likely that exercise can improve a person’s mood as well as
their sleep.
194 R. Brown and E. Thorsteinsson
Mechanistically, volitional physical activity/exercise causes a transient
increase in BT [131], which is paralleled by an increase in heart rate
[132], energy expenditure and the production of body heat. This activity-
related increase in BT tends to be maximal when the activity occurs at
around the trough of the circadian rhythm (4–6 a.m.), and it is smallest
at the peak of the resting circadian rhythm of core BT (4–5 p.m.) [133].
Even non-volitional physical activity is linked to an increase in BT; for
example, psychomotor changes in Alzheimer’s disease patients were related
to a change in BT, especially psychomotor agitation (i.e. high nocturnal
activity, later peak in activity), which was related to a phase-shift in the
circadian rhythm of core BT (later core BT peak) and higher core BT, rel-
ative to healthy controls [134]. Furthermore, spontaneous physical activity
(SPA, i.e. unplanned biologically driven behaviour such as fidgeting, foot-
tapping, restlessbehaviour and activities ofdaily living; e.g.talking and the
maintenance of posture) can transiently increase a person’s BT [135, 136].
Thus, volitional and non-volitional physical activity transiently increases
BT; if the activity occurs just prior to bedtime, it may tend to interfere
with sleep onset, by interfering with the normal evening decline in BT
[137]. Interestingly, the positive effects of exercise on mood are thought
to be at least partly mediated by the transient increase in core BT during
exercise, which could potentially reset the circadian rhythm of BT [138].
However, paradoxically, a sedentary lifestyle is also linked to an elevated
BT (e.g. increase in scrotal temperature in male sedentary workers) [139].
Taken together, the results suggest that a nonlinear relationship is likely
to exist between physical activity and BT, such that physical activity and
physical inactivity can both increase a person’s BT. However, it is not clear
whether the elevated BT in sedentary individuals is transient (like the
effects of physical activity) or if the change in BT tends to persist over
time.
Physical inactivity is also known to be related to high BMI [140]and
higher overweight/obesity risk in non-obese individuals [141]. In con-
trast, physical activity can assist people to control their weight [142], and
it facilitates long-term weight loss in overweight people [143], includ-
ing in combination with dietary restriction [144]. A recent systematic
review showed that long-term weight loss was related to higher physical
activity levels, but the relationship was dependent upon the participants’
7 Arousal States, Symptoms, Behaviour, Sleep … 195
adherence to the activity regimen [145]. That is, volitional physical activ-
ity programmes are an effective agent that promotes weight loss in some
overweight/obese people [145], but its’ effects will tend to be suboptimal
if the activity is of low intensity or the participants fail to properly adhere
to the activity programme [146].
Importantly, most (>75%) of a person’s daily energy expenditure is
linked to basal metabolism, food intake (i.e. diet-induced thermogenesis)
and cold exposure (i.e. non-shivering thermogenesis), rather than physical
activity [147]. In total, physical activityis comprised of obligatory physical
activity (i.e. survival-oriented activities), voluntary physical activity (e.g.
exercise) and SPA. Together, they are the strongest environmental determi-
nants of total body and central abdominal fat mass. However, our obligate
activity needs are largely absent in modern life and so, in practice, vol-
untary exercise/physical activity tends to exert little effect upon our total
energy expenditure over time [147].
In contrast, most of the variability in daily energy expenditure (above
baseline and independent of body size) is due to variability in SPA. SPA is
linked to the expenditure of about 100–800 kcal/day [148, 149], and it
contributes about 10% to the variability in BMI, similar to the proportion
that is contributedby basal metabolic rate(12%) [150, 151]. Of particular
relevance here, SPA has been shown to be inversely correlated with body
weight andweight gain [152],such that overweight/obeseindividuals tend
to show a dramatic decrementin SPA (i.e. 2 hours less/day) relative to lean
individuals [153], who tend to be more active, restless and spend less time
sitting or lying in bed, thereby burning more calories [150]. That is to
say, SPA can contribute significantly to daily energy expenditure in lean
people, but it appears to be greatly deficient in overweight/obese people.
Physiologically, non-exercise activity thermogenesis (NEAT) is the energy
that is expended during SPA. NEAT is thought to protect lean individu-
als from gaining weight during a caloric challenge by increasing activity
levels after the overfeeding and decreasing them with underfeeding [149,
151]. NEAT is elevatedin conjunction with high-intensity training [154],
resistance training [155] and active work (e.g. agricultural and construc-
tion work), relative to sedentary office work [156]. In contrast, NEAT is
markedly lowerin overweight/obese individuals relative to lean or normal-
weight individuals [157], suggesting that a deficit in SPA (and NEAT) in
196 R. Brown and E. Thorsteinsson
overweight/obese people can contribute to weight gain over time. As dis-
cussed in Chapter 9, interventions that are capable of increasing SPA and
NEAT may represent possible new targets for weight loss therapy [149],
but so far, the premise has yet to be tested empirically.
Finally, prolonged sitting has recently been shown to predict an elevated
mortality risk. In a study of 222,497 adults enrolled in the Australian 45
and Up Study, sitting time was found to be positively related to all-cause
mortality, after adjusting for sex, age, education, urban/rural residence,
physical activity, BMI, smoking, self-rated health and disability. All-cause
mortality hazard ratios ranged from 1.02 (4–8 hours sitting/day) to 1.15
(8–11 hours sitting/day) to 1.40 (≥11 hours sitting/day), and they were
consistent across genders, age groups, BMI categories, physical activity
levels and healthy part icipants vs. people with pre-existing cardiovascu-
lar disease or diabetes mellitus [158]. Taken together, the results suggest
that prolonged sitting is a significant risk factor for all-cause mortality,
although the mechanism underpinning this relationship has so far not
been determined.
Nonetheless, a small study of 11 healthy men has shown that rectal
temperature, which is similar to core BT, was highest in people while they
were standing (37.47°C), slightly lower when they were sitting (37.26 °C)
and lowest when they were supine (36.87 °C), whereas skin temperature
was highest when supine (34.04 °C) and lower when either sitting or
standing (33.49vs. 33.48 °C),respectively [159].In another study, normal
sitting was associated with reduced blood flow volume and temperature
in the lower extremities [160]. Taken together, the results indicate that
different body locations provide a slightly different estimate of peripheral
BT, which is typically lower than a person’s core BT [161], whereas a
change in posture can induce a change in BT, with higher BT detected in
people who are standing or sitting.
In summary, in the scientific literature, physical inactivity and a
sedentary lifestyle are linked to impaired sleep, affective distress and
overweight/obesity, whereas physical activity can improve sleep, mood
and weight. Furthermore, a bidirectional relationship has been detected
between physical inactivity, impaired sleep, affective distress and over-
weight/obesity, as detailed above and in Chapter 3. However, it is not
exactly clear how the different phenomena are related to each other, other
7 Arousal States, Symptoms, Behaviour, Sleep … 197
than being temporally related. Nevertheless, an elevated BT (linked to
physical inactivity) may parsimoniously explain the onset of sleep prob-
lems (e.g. phase-shift in the sleep-wake cycle) in sedentary individuals;
over time, impaired sleep may contribute to low mood and weight gain,
as detailed above, in the next section, and in Chapters 3 and 6.
7.4 Behaviour Linked to Impaired Sleep
and Elevated Body Temperature
Many different sleep-disrupting behaviours have been examined in regard
to sleep, and in most cases, the behaviour is also linked to an elevated
BT. For example, in Chapter 3, we saw that late-night eating can interfere
with sleep onset. It also tends to coexist with stress, affective distress and
overweight/obesity, and it is associated with an elevated nocturnal BT.
Similarly, many of the sleep-disrupting behaviour discussed in this section
can interfere with sleep, and they are risk factors for other chronic condi-
tions, including overweight/obesity, anxiety/depression and some physical
health problems.
For example, electronic device use (e.g. smartphones) is reported to
adversely impact upon sleep,possibly viathe effectsof bright light exposure
and/or increased nocturnal BT. A recent poll of 1508 Americans showed
that 90% of them had used a device within 1 hour of bedtime, with
older people (aged > 30 years) tending to favour TV watching, whereas
younger people (<30 years) tended to use their mobile phones. Mobile
phones are argued to be more interactive than just passively watching TV,
and as a result, their use is reported to be more strongly correlated with
disturbed sleep [162]. Specifically, mobile phone use, especially excessive
text-messaging, has been linked to poor sleep quality (but not shorter
sleep duration) in university students [163]. In contrast, Gamble and col-
leagues [164] found that a dose-dependent relationship existed between
adolescents’ use of the devices in the bedroom and shorter sleep duration
on weeknights; that is, the more they used their phone in bed, the shorter
their sleep duration was on weeknights. The results suggest that mobile
phone use at night can potentially shorten sleep and reduce sleep quality,
especially if the users use the device/s in bed or text excessively; in which
198 R. Brown and E. Thorsteinsson
case, they may struggle to disengage from the phone and prepare them-
selves for bed or be hyper-vigilant to the point that they are aware of any
notifications or messages that are sent late at night.
Similarly, television, computer, gaming console, tablet and audio player
use is suggested to adversely impact on sleep [165]. In one study, the use
of a computer (e.g. watching movies) or mobile phone in bed was linked
to greater insomnia severity, after controlling for gender and age, but not
tablet use, gaming or listening to music, in a large student study.However,
the latter non-significant results may be due to the relatively infrequent
useofthedevicesbytheparticipants[165]. Only one study appears to
have compared electronic book reader use vs. reading a printed book at
night, showing that electronic reader use was related to longer sleep onset
latency, reduced evening sleepiness and melatonin secretion and delayed
timing of the circadianrhythm by 1.5 hours [166].Thus, electronic reader
use may disrupt a person’s sleep and promote wakefulness at night, which
is alarming, given the common use of the devices at night or while in bed
[162].
Electronic device use (e.g. mobile phone) has also been linked to worse
mental health, including a greater risk of anxiety and depression [167].
In addition, night-time electronic device use is related to an elevated risk
of overweight/obesity in children; reduced physical activity is thought to
drive this relationship [168]. However, few studies have longitudinally
examined electronic device use in relation to physical and mental health.
One study showed that high mobile use was linked to high stress, depres-
sion and impaired sleep in adult males and females; in particular, the
greater use of the devices was related to worse sleep and depression in
men, and worse depression in women 1 year later [169]. Similar results
have been obtained in a study of computer use, email/chat use and com-
puter gaming, at baseline and 1 year later, in young adults [170], in which
excessive computer use was shown to be a risk factor for sleep problems
1 year later (in men) whereas excessive email/chat use was correlated with
poor mental health (in women). Taken together, the results suggest that
electronic device use at night may interfere with the onset of sleep and
contribute to mental ill-health—depending on the type, frequency and
intensity of the use. Use of the devices may also predispose children to
gain weight over time via the adoption of a sedentary lifestyle. However,