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SLEEP AND HEALTH
causal relations. Menopause seems to involve disrupted sleep in relation to hot flushes,
depression/anxiety and sleep-disordered breathing. Oestrogen is associated with
improved sleep quality but it is not clear whether the effects are due to a reduction
of hot flushes. Oestrogen also improves sleep-disordered breathing.
With respect to background factors, age is an established predictor of disturbed sleep
(Karacan et al., 1976; Bixler, Kales and Soldatos, 1979; Ancoli-Israel and Roth,
1999; Ribet and Derriennic, 1999; Leger et al., 2000; Sateia et al., 2000).
Interestingly, however, older age may be related to a lower risk of impaired awakening
(Åkerstedt et al., 2002c), that is, in this study it was easier to wake up and one
felt better rested with increasing age, while at the same time sleep quality was lower.
The increased risk of disturbed sleep is consistent with the increasingly strong interference
of the circadian morning upswing of the metabolism with increasing age
(Dijk and Duffy, 1999). Thus sleep maintenance is impaired and when sleep is interrupted
“spontaneously”, the awakening is, by definition, easily accomplished and
will be lacking in inertia. This ease of awakening may be interpreted as “being wellrested”,
and obviously the need for sleep is not great enough to prevent an effortless
transition into wakefulness.
In addition, sleep homeostasis seems to be weakened with age in the sense that sleep
becomes more fragmented and SWS or power density in the delta bands decrease
(Williams, Karacan and Hursch, 1974; Bliwise, 1993; Dijk et al., 1999). As mentioned
above, the effects are more pronounced in males, a fact that may be linked to
reduced levels of growth hormone and testosterone.
2.3.3 PERSONS EXPOSED TO STRESSORS AS A RISK GROUP
A number of epidemiological studies point to a strong link between stress and sleep
(Åkerstedt, 1987; Urponen et al., 1988; Ancoli-Israel and Roth, 1999). In fact, stress
is considered the primary cause of persistent psychophysiological insomnia (Morin,
Rodrigue and Ivers, 2003). That stress can affect proper sleep seems obvious, but
Vgontzas et al. (2001) at Pennsylvania State University College of Medicine have
found another reason why middle-aged men may be losing sleep. It is not just
because of what they worry about; rather, it is due to “increased vulnerability of
sleep to stress hormones”.
As men age, it appears they become more sensitive to the stimulating effects of corticotropin-releasing
hormones (CRH). When both young and middle-aged men were
administered CRH, the older men remained awake longer and slept less deeply.
(People who don’t get enough of this “slow-wave” sleep may be more prone to
depression.)
The increased prevalence of insomnia in middle age may, in fact, be the result of
deteriorating sleep mechanisms associated with increased sensitivity to arousal-producing
stress hormones, such as CRH and cortisol. In another study, the researchers
compared patients with insomnia to those without sleep disturbances. They found
that “insomniacs with the highest degree of sleep disturbance secreted the highest
amount of cortisol, particularly in the evening and night-time hours”, suggesting
that chronic insomnia is a disorder of sustained hyperarousal of the body’s
stress response system. Also, recent epidemiological studies have shown a connection
between disturbed sleep and later occurrence of stress-related disorders such
as cardiovascular diseases (Parish and Shepard, 1990; Nilsson et al., 2001;
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