Handbook of Psychology

Insomnia: Scope of the Problem 323

persistence of sleep disturbances may prevent or delay recov-
ery from depression (Kennedy, Kelman, & Thomas, 1991).
Finally, there is evidence that depression can be both a risk
factor for insomnia and a potential consequence of chronic
insomnia. Vollrath et al. (1989) found that 46% of subjects
suffering from periodic or chronic insomnia reported experi-
encing depression and anxiety in the year prior to interview.
Conversely, two other studies have shown that chronic in-
somnia increases the risk of developing major depression
(Breslau et al., 1996; Ford & Kamerow, 1989).

Sleep and Health

There is extensive evidence showing that sleep and health are
related. On the one hand, health problems can be a risk factor
for insomnia; while on the other hand, poor sleep may have a
negative impact on immune function and on recovery from
physical illness. Individuals with insomnia report a higher
frequency of health problems, medical consultations, and
hospitalizations relative to good sleepers (Gislason &
Almqvist, 1987; Kales et al., 1984; Mellinger et al., 1985;
Simon & VonKorff, 1997). Physical complaints most fre-
quently reported by individuals with insomnia include gas-
trointestinal problems, respiratory problems, as well as
headaches and nonspeci“c aches and pain (Kales et al., 1984;
Vollrath et al., 1989). Chronic conditions such as cardiopul-
monary disease, painful musculoskeletal diseases, and back
problems have also been observed more frequently in pa-
tients with insomnia than in good sleepers (Gislason &
Almqvist, 1987; Katz & McHorney, 1998). Surveys of pa-
tients with various medical conditions have also yielded very
high rates of insomnia complaints. For example, patients
with neurological (e.g., Parkinson•s disease, multiple sclero-
sis, Alzheimer•s disease), gastrointestinal, renal, and car-
diopulmonary diseases (e.g., asthma) all seem at higher risk
for secondary sleep disorders, including insomnia (Pressman,
Gollomp, Benz, & Peterson, 1997; Walsleben, 1997). Re-
search conducted with an elderly sample has shown that poor
physical health was the strongest risk factor for insomnia,
even though mental health factors were also related to poor
sleep (Morgan & Clarke, 1997).
In a recent study conducted by our team, 51% of women
who had been treated for nonmetastatic breast cancer re-
ported insomnia symptoms (Savard, Simard, Blanchet, Ivers,
& Morin, 2001). This “nding was consistent with results ob-
tained in patients with other types of cancer, in which preva-
lence rates of insomnia symptoms ranged from 30% to 50%
(Savard & Morin, 2001). In a comparative study, 40% of can-
cer patients (mixed diagnoses) reported sleep dif“culties
compared to only 15% of control participants with no severe
illness (Malone, Harris, & Luscombe, 1994), suggesting that

insomnia is much more prevalent in cancer patients than in

the general population. As in other medical conditions, fac-

tors that may produce sleep disturbances include the direct

physiological effects of the illness, the side effects of cancer

treatment (e.g., hot ”ashes associated with chemotherapy and

hormone therapy), pain, and the psychological reaction to the

cancer diagnosis and treatment. Although the cross-sectional

nature of these data precludes any conclusion about causality,

these “ndings still suggest a very high rate of comorbidity

between sleep and health problems.

Insomnia and Longevity

Further evidence for a link between insomnia and health is

provided by data from prospective epidemiological surveys

indicating that sleep disturbance is associated with increased

mortality. Individuals who reported sleeping less than 4

(Kripke, Simons, Gar“nkel, & Hammond, 1979) or 6

(Wingard & Berkman, 1983) hours per night had a mortality

rate (all causes combined) 1.5 to 2.8 times higher six and nine

years later compared to individuals sleeping between 7 to 8

hours each night. Longer sleep durations (i.e., more than 9 or

10 hours of sleep per night), as well as the long-term use of

sleep medications, were also associated with higher mortality

rates (Kripke et al., 1979; Wingard & Berkman, 1983). In an-

other study, Enstrom (1989) observed a very low risk of mor-

tality (including mortality due to cancer) in Mormon high

priests, a church promoting good health practices. This effect

was most evident in those who exercised regularly, obtained

proper sleep (generally 7 to 8 hours each night), and who had

never smoked cigarettes, as assessed eight years earlier.

Although sleep duration seems to be related to longevity,

insomnia per se is a condition characterized by several symp-

toms other than a shorter sleep duration (e.g., emotional

distress). As such, these “ndings may not generalize to in-

somnia. Such a cautious interpretation is warranted since

subjective sleep dif“culties have not been found to be as

strong a predictor of mortality as total sleep time (Kripke

et al., 1979; Wingard & Berkman, 1983). More importantly,

these studies did not control for potential confounding vari-

ables such as the presence of preexisting medical conditions.

For example, it is likely that individuals who sleep for a

longer period of time do so because they already have a major

medical illness.

Insomnia and Immunity

Another potential effect of insomnia on health is immune

down-regulation. Although some studies have shown a

deleterious effect of experimental sleep deprivation on im-

mune functioning (Dinges, Douglas, Hamarman, Zaugg, &