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Naps
Last edited |
06/18/2006
Epidemiological data in the general population on daytime
napping are scarce
This paucity of information reflects a disinterest from
epidemiologists probably due to such popular beliefs that napping is a benign
lifestyle habit shared mostly by elderly persons or a cultural phenomenon
encountered primarily in warm, southern climates.
Numerous clinical studies, however, have explored:
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the function of napping in the circadian rhythm
(Campbell & Zulley, 1989; Zulley & Campbell, 1985),
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its possibility in the treatment of narcolepsy (Roehrs
et al., 1986; Garma & Marchand, 1994),
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its effects in adaptating to shift work (Dinges et
al., 1988; Chan et al., 1989; Bonnet, 1990; Rosa, 1993) and
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its role in the
sleep of the elderly (Buysse et al., 1993).
Clinical evidence clearly shows that napping increases
linearly with age (Tune, 1969; Kronholm & Hyyppa, 1985).
This suggests that
sleep physiology changes as a function of age: napping is often considered a
normal characteristic of aging on a part with other sleep problems, most
notably, disrupted sleep (Carskadon et al., 1980).
Research
We explored the relationship between naps, sleep/wake schedule,
sleep symptoms, sleep and mental disorders in a representative sample of the
non-institutionalized German population composed of 2216 women and 1899 men aged
15-99 years.
A telephone interview survey was performed by lay interviewers using the Sleep-EVAL
system.
Results
Napping on at least 2 days per week was cited by 22.2% (95% confidence interval: 20.9% to 23.5%) of the sample and
increased linearily with age, reaching 53.3% in subjects 75 years of age and over.
Presence of daytime sleepiness was positively associated with
napping for all age groups.
In subjects younger than 65 years, napping was also related to:
In elderly subjects (over 75 years),
only the report of daytime sleepiness and primary snoring were
related to napping.
The results show that there are numerous differences between nappers and non-nappers
within different age groups:
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The sleep of nappers under 65 is characterized by an
irregular sleep-wake schedule, a shorter sleep time, and a longer sleep
latency compared with their non-napping counterparts.
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Similarly, younger nappers present with many
pathological symptoms or disorders (e.g., cataplexy-like symptoms and mental
disorders) not observed in non-nappers in the same age group.
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Elderly nappers have higher occurrence of sleep leg
disorders (Periodic limb movment disorder, nocturnal leg cramps or restless
leg syndrome), insomnia symptoms, use of sleep medication and physicial
diseases.
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Nappers under 65 years of age have a higher
occurrence of depressive disorders, feel more often that napping is
unrefreshing, and have their night sleep affected by napping. They are also
more likely than elderly nappers to have at least one dysomnia and/or mental
disorder.
This suggests that the presence of napping in the younger age
groups (<65 years of age) is the consequence of lifestyle and/or of pathology,
whereas in the elderly, it is explained in part by disruptive events occurring
at night, namely, nocturnal awakenings and primary snoring.
This last finding
was also observed in laboratory studies (Buysse et al., 1992).
In the elderly, it appears that good or poor sleep has little
impact on the presence of daytime naps. One hypothesis is that there is a
decline in the amplitude of the circadian rhythm in the sleep propensity of the
elderly (Carskadon et al., 1980, Buysse et al., 1992).
This hypothesis is supported by the fact that bedtime occurs about 30 minutes
earlier for the elderly compared with younger subjects and that overall sleep
time including naps is comparable across age groups.
This suggests a redistribution of sleep over a 24-hour period (Kronholm & Hyyppa,
1985; Buysse et al., 1991; Gerard et al., 1978; Hayter, 1983; Gerber et al.,
1985; Liberman et al., 1989; Webb, 1982).
Another explanation was put forward by
Broughton (1989).
According to this author, the human sleep/wake rhythm could be
a biphasic one with a two per day rhythm of sleep: a main sleep period occurring
at night and a napping period in the mid afternoon. However, societal
requirements are not designed to respect this biphasic sleep/wake pattern.
In
fact, industrialization and productivity are not compatible with daytime
napping, which is further illustrated in our data by the dramatic increase in
the percentage of men who nap once they are retired and by the higher proportion
of non workers who nap.
Similarly, previous studies (Webb & Aber, 1984) have shown
that daytime napping has little effect on the night sleep of the elderly.
This
is in line with the claims made by the elderly in our study.
An alternative
explanation is that most elderly persons have little or no life constraints
preventing them from napping whenever they feel the urge.
This was reported in
other studies (Garma & Marchand,1994; Spiegel, 1981) which observed that
opportunity is an important factor in napping.
This may explain the higher
proportion of nappers among retirees, students and the unemployed. However, in
the elderly group, other psychosocial factors such as loneliness (Minors et al.,
1989; Monk, 1989) and boredom (Webb & Swinburne, 1971) may also affect changes
to sleeping habits.
Conclusion
Is napping a benign lifestyle habit or should physicians take note?
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First, one should consider that most nappers do not have any sleep or mental
disorders: about two thirds of the subjects younger than 65 years of age and
four out of five among the elderly did not have any sleep or mental disorders in
this study.
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However, further
examination is required about the age of the subject.
In subjects under 65, the physician should look for
other excessive daytime sleepiness symptoms since napping may indicate a sleep
disorder of excessive sleepiness that requires medical attention such as
narcolepsy or hypersomnia.
The sleep quality should also be investigated,
especially symptoms of disordered breathing. Snoring and sleep apnea are
likely to produce daytime somnolence.
Investigation of sleep habits is also
indicated.
Poor sleep hygiene but also circadian rhythm disturbance may be
responsible for daytime napping.
Finally, the possibility of a
mental disorder
should also be considered.
Among the elderly, napping appears to be a common
habit that is reported by about half of this age group.
However, it does not
exclude the possibility of an underlying sleep disorder especially those
likely to deteriorate the quality of sleep such as snoring, restless legs
syndrome, and periodic leg movement disorder.
From Ohayon MM, Zulley J.
Prevalence of Naps in the general population. Sleep & Hypnosis
1999; 1:88-97.
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