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Cognition
and
Daytime Sleepiness
Last edited |
10/25/2008
Recent findings suggest it may
have a relationship between excessive daytime sleepiness (EDS) and
cognitive deficits
In industrialized countries, the number of elderly people
continues to grow.
The health care systems must be prepared to support this
fast-growing part of the population, whose needs are specific: the
elderly population is vulnerable to a high occurrence of organic
diseases and to cognitive impairments that will affect the quality of
life.
The prevalence of mild to important cognitive deficits is
usually set between 4% and 10% in the elderly population living in the
community (1,2,3).
Obviously, individuals with severe cognitive disorders
related to dementia are rarely found in the community because they are
quickly losing the autonomy necessary to live in the community.
Several longitudinal studies have put forward an
increased risk of mortality in non-demented elderly individuals with
cognitive impairments (4-8).
The adjusted relative risks (for age, sex, health status)
of mortality was found to be 1.7 to 3.6 times higher in elderly with
mild to severe cognitive impairments (4-12).
Some longitudinal studies showed that the mortality rate
was not statistically different in any age group among subjects with
good cognitive performance, and that the preservation of cognitive
functions was associated with better survival in old individuals
(11,13,14).
The decline in cognitive performance has been associated
with several factors, including neurological diseases, vascular
diseases, depression (16,17,18) and diabetes (15) but not always (19).
However, other factors significantly accounted for this
decline in the aging process; namely, the educational level (20,21) and
social disengagement (22).
More recently, excessive daytime sleepiness has been
associated with poor cognition and dementia (23).
Moreover, an increased mortality risk of 1.73 was found
in elderly individuals with cognitive impairments napping most of the
time (24).
This study
aimed to determine to which extent EDS is predictive of cognitive
impairment in an elderly population.
Methods
1,026
subjects 60 years of age or older, representative of the general
population living in the metropolitan area of Paris (France), were
interviewed by telephone using the Sleep-EVAL expert system.
To find
these subjects, 7,010 randomly selected households were called: 1,269 of
them had at least one household member in this age range (participation
rate: 80.9%).
In
addition to DSM-IV and ICSD diagnoses, the system administered to
participants the Psychological General Well-Being Schedule; the
Cognitive Difficulties Scale (Mac Nair-R) and an independent living
scale.
Results
Excessive Daytime Sleepiness
EDS was reported by 13.6% of the sample with no
significant difference among age groups.
Compared to non-sleepy subjects, those with EDS were
at increased risk of cognitive impairment on all the dimensions of the
Mac Nair-R scale after controlling for age, gender, physical
activity, occupation, organic diseases, use of sleep or anxiety
medication, sleep duration and psychological well-being.
The odd ratios were: 2.1 for attention-concentration
deficits; 1.7 for praxis; 2.0 for delay recall; 2.5 for difficulties in
orientation for persons; 2.2 for difficulties in temporal orientation
and 1.8 for prospective memory.
Napping
The proportion of subjects taking a nap at least two days
per week was 30.1%.
The percentage of nappers increased with age: 22.4% of
subjects between 60 and 64 years napped.
This was the case with 29.3% of individuals between 65
and 69 years of age; 34.3% of those between 70 and 74, and 33.8% of
those 75 or older (c2=11.053; df=3; p=.01).
Most of them were taking only one nap per day (90.4%).
Among the nappers, 14.6% had non-intentional naps; i.e.,
they were not planned. The proportion of non-intentional nappers was
comparable in each age group.
Intentional napping was associated with a
higher score on difficulties in orientation for persons as compared to
subjects who never napped.
Subjects who took non-intentional naps had higher scores
on attention-concentration deficits, delay recall, difficulties in
orientation for persons and difficulties in temporal orientation (Table
3).
Intentional nappers reported slightly but not
significantly more frequently to feeling sleepy during the daytime
(14.0% vs. 9.5%; p=.06).
The association between intentional naps and excessive
daytime sleepiness was significant only in the two younger groups. In
subjects between 60 and 64 years old, 19.5% of intentional nappers
reported excessive daytime sleepiness as compared with 8.7% of the non-nappers
(p<.05).
In subjects between 65 and 69 years, 15.8% of intentional
nappers also reported having excessive daytime sleepiness as compared
with 5.6% in the non-nappers (p=.02).
Organic
diseases
Overall, 27% of the subjects in the study were suffering
from an organic disease. The most frequently reported diseases were
arthritic diseases (20.2%), hypertension (17.3%) and heart diseases
(10.5%). The prevalence of organic diseases was higher in the two oldest
groups (70-74 y.o.: 34.6%; ≤ 75 y.o. 31.7%) when compared with the two
younger groups (60-64 y.o.: 18.7%; 65-69 y.o.: 25.2%; c2=18.833; df=3;
p<.001).
These subjects achieved higher scores on five of the six
dimensions of the Cognitive Difficulties scale: attention-concentration
deficits, praxis, difficulties in orientation for persons, difficulties
in temporal orientation and prospective memory (Table 4).
Obstructive sleep apnea syndrome
OSAS was found in 2.6% of the sample with no significant
difference among age groups.
Generally speaking, OSAS subjects obtained comparable
cognitive difficulties scores except on prospective memory, where the
scores were significantly higher (Table 4).
DISCUSSION
To our knowledge, this is the first study that aimed to
verify whether excessive daytime sleepiness is an independent predictive
factor for cognitive difficulties in elderly individuals living in the
community.
Our results
clearly showed that excessive daytime sleepiness is a strong
predictive factor for cognitive difficulties in elderly even after
controlling for possible confounding effects of age, gender,
physical activity, occupation, organic diseases, use of sleep or
anxiety medication, napping and mental diseases.
In our sample:
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14.1% of individuals 65 years and older had moderate
to severe daytime sleepiness.
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Napping at least two days per week was reported by
32.6% of the subjects aged 65 years and over;
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14.5% of the elderly were taking a nap daily.
Excessive daytime sleepiness should be distinguished from
intentional naps.
The latter may not reflect the presence of a sleep
disorder and can be a healthy habit in the elderly.
The increasing rate of napping with age is probably due
greatly to the fact that older people have little or no life constraints
preventing them from napping whenever they feel the urge, and rarely
does this constitute a social problem.
There was no association between intentional napping and
excessive daytime sleepiness in the elderly in this study.
The association was, however, significant in younger
subjects of our sample.
These younger subjects were mostly still working and
therefore could not nap when they felt the need.
If intentional napping is rather harmless, excessive
daytime sleepiness can be the expression of a more important underlying
disorder; for example, a sleep-related breathing disorder or depression
(16-18,41-44).
Significance of excessive
daytime sleepiness
In this study, we found that excessive daytime
sleepiness is an independent predictive factor of a variety of cognitive
difficulties that may impair the quality of life.
Elderly subjects who participated in this study were
non-demented and had enough autonomy to still live in the community.
However, excessive daytime sleepiness and cognitive
difficulties were both related in our study to a decreased ability to
perform activities of daily living.
There was also the possibility that elderly individuals
who were retired or who had fewer domestic obligations received less
stimulation and therefore were more sleepy during the day.
This could be deduced by the increasing number with age
of subjects who took a nap during the day.
However, from the results of the logistic regressions
that we performed, it appears that age was not a major factor for the
presence of cognitive difficulties and napping was not related at all.
Older age was an independent predictive factor on only
two of the seven cognitive measures: praxis and memory deficits on the
Mini-Mental State.
An independent predictive factor, that may be
surprising at first for difficulties in orientation for persons and
prospective memory, was the presence of an occupation.
However, it is not so astonishing: the cognitive
difficulties scale is based on a self-report of daily living
difficulties.
An individual who is still active is more likely to be
confronted with a decline in his cognitive abilities than a person who
has retired from active life.
This is confirmed by the fact that this factor was not
predictive of memory deficits when we used the results on memory from
the Mini-Mental State examination, where memory is more objectively
assessed.
Furthermore, active individuals at any age in our study
less frequently reported being limited in their travels and in their
capacity to do their shopping, two activities that are narrowly related
to the items assessed in the prospective memory (need of a list when
shopping, forgetting the things that s/he was planning to buy).
What can be the mechanism that explains the predictive
value of daytime sleepiness for cognitive difficulties?
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A possible explanation is that other disorders such
as a mental, an organic pathology or an obstructive sleep apnea
syndrome (OSAS) caused daytime sleepiness.
Recently OSAS, for which daytime sleepiness is a cardinal symptom,
has been found to cause cognitive deficits because of the repeated
anoxia provoked by breathing pauses during sleep (41,42).
However, this explanation does not fully explain our findings.
Indeed, the multivariate models controlled for the effects of these
three types of pathologies, and daytime sleepiness still emerged as
a strong independent predictor of cognitive difficulties.
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Another possibility is that daytime sleepiness may be
due to a lack of cognitive and/or social stimulations.
Several studies have shown that when elderly people receive
cognitive stimulation and are kept socially active, the likelihood
of cognitive decline decreases (22,48,49).
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Another possible explanation is that daytime
sleepiness is an early indicator that may predict subsequent
cognitive decline.
However, longitudinal studies are needed to confirm this hypothesis.
Conclusions
In summary, these data from a community-based sample
indicated that excessive daytime sleepiness is a good predictor of
cognitive difficulties.
Physicians who treat elderly patients with such
complaints should be aware that these patients are at greater risk to
have cognitive deficits.
As shown in longitudinal studies, it is possible to delay
or to prevent these cognitive deficits by keeping up intellectual
stimulation and by promoting social engagement in these elderly
individuals.
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Sleep-EVAL
Research
