Sleep
10(4):297-305, Raven Press, New York
© 1987, Association of Professional Sleep Societies
Excessive Daytime Somnolence in Young Men:
Prevalence and Contributing Factors
*M. Billiard, A. Alperovitch, C. Perot, and A. Jammes
*Unite des Troubles du Sommeil, Montpellier; INSERM U.
169, VillejuiJ; Centre de Selection,
Tarascon; and Centre de Selection, Fort Neuf, Vincennes, France
Summary: To investigate the prevalence of excessive daytime somnolence and
contributing factors, 58,162 draftees between 17 and 22 years of age, registered
in two selection centers of the French army, were screened by means of a
17-item questionnaire. In response, 8,201 subjects (14.1 %) reported occasional
daytime sleep episodes, 2,210 (3.8%) one or two daily episodes, and 640 (1.1 %)
more than two daily episodes. Of the total sample, five percent or 2,933 considered these sleep episodes to affect their lives. Different possible factors of
daytime sleep episodes were investigated, including hours of nocturnal sleep,
sleep-wake schedule, sleep difficulties, use of hypnotics, snoring, and occurrence of cataplexy. A strong association was found between these factors and
excessive daytime somnolence. A stepwise multivariate analysis was performed on five of these factors: hours of nocturnal sleep, sleep-wake
schedule, sleep difficulties, use of hypnotics, and snoring. All five factors were
shown to be independently related to excessive daytime somnolence and were
ranked in the following descending order: use of hypnotics, sleep difficulties,
irregular sleep-wake schedule, snoring, and hours of sleep. Key Words: Cataplexy - Excessive somnolence - Hypnotics - Sleep difficulties - Sleepwake schedule-Snoring.
Excessive daytime somnolence is an often neglected, yet rather common, symptom
and a potential source of traffic or work accidents, low professional efficiency, and
unsuccessful academic achievement. It heads the list of symptoms characterizing alertness disorders, either independent disorders such as narcolepsy, idiopathic hypersomnia, recurrent hypersomnias, or dependent ones, such as the hypersomnia sleep
apnea syndrome and the disorders of excessive somnolence related to psychophysiological or psychiatric conditions, chronic intake of psychotropic drugs, and insufficient
sleep. Previous epidemiological studies have been devoted to a few well-defined conditions, such as narcolepsy, the hypersomnia sleep apnea syndrome, and general surveys
on sleep disorders including the evaluation of "excessive daytime somnolence," but
there has been no specific epidemiological survey of excessive somnolence.
The first epidemiological study on narcolepsy found an occurrence of 0.02% in the
Accepted for publication December 1986.
Address correspondence and reprint requests to Dr. Michel Billiard at Unite des Troubles du SommeiI,
Centre Gui de Chauliac, 34059 Montpellier, France.
297
298
M. BILLIARD ET AL.
recruits of the United States Navy (1). Later; Dement et al. conducted two surveys,
the first, in the San Francisco Bay area, leading to a conservative estimate of 0.05%
(2), and the second, in Los Angeles and Orange counties, concluding that the prevalence of narcolepsy is 0.067% (3). Concerning the hypersomnia sleep apnea syndrome,
a study conducted in the San Raffaelo Hospital in Milan indicated a prevalence of
0.99% (4) and another, in industrial workers of Israel, gave a similar estimate of 1.03%
(5).
Symptoms of excessive daytime somnolence vary according to the samples, the
number of people investigated, and the types of questions used. Of 2,466 Scottish subjects questioned, 0.5% reported "too much sleep" (6). The prevalence of "hypersomnia" was 4.2% among 1,006 representative households in the Los Angeles metropolitan area (7). Of 1,502 Israeli industrial workers, 4.9% were shown to have "excessive daytime somnolence" (8). Of 2,552 Finnish army recruits questioned shortly after
entering service, 9.5% answered positively to the question "Do you consider yourself
more sleepy during the daytime than your friends or workmates?" (9) In a study conducted among 5,713 citizens of the Republic of San Marino, "sleepiness independent
of meal times" was found in 8.7% of all respondents, in 17.5% of those between the
ages of 10 and 19 years, and in up to 33.8% of those between the ages of 15 and 16 (10).
Finally, "daytime sleepiness" was indicated by 16.2% of 1,138 male subjects between
the ages of 18 and 23 years in a questionnaire distributed in Milan (11).
In an effort to obtain more precise data and to identify and compare the different
factors of excessive somnolence, we screened over 60,000 draftees of the French army.
METHODS
The study was conducted in two selection centers, Vincennes (near Paris) and Tarascon (southeastern France) in 17 -22-year-old draftees. Military service is still compulsory in France, and French men are called up in selection centers for a series of orientation tests prior to their enlistment. A 17-item questionnaire was designed specifically
for this study. * The questionnaire, completed under the supervision of noncommissioned officers, was presented to the draftees as part of a scientific study to encourage
honesty.
Of 61,344 questionnaires distributed, 3,472 were discarded either for incoherentness
or for age outside the 17-22-year-old group. A total of 58,162 valid questionnaires,
30,815 from Vincennes and 27,347 from Tarascon, were eventually processed. Statistical tests included t tests, Pearson's chi-square and, when required, adjustment tests
to control confounding factors. Due to sample size, almost all p values were very
small, even if differences were not of practical significance. Consequently, we chose p
< 0.01 as the minimum level for statistical significance.
RESULTS
Number of subjects with daytime sleep episodes
Occasional daytime sleep episodes independent of meal times were reported by
8,201 subjects (14.1%); 2,210 (3.8%) reported one or two daily episodes and 640 (1.1%)
* Available on special request to the authors.
Sleep, Vol. 10, No.4, 1987
299
PREVALENCE OF EXCESSIVE SOMNOLENCE
TABLE 1. Number of sleep hours per night and percentages of subjects with no, occasional,
one or two, or more than two daytime sleep episodes (DSE)
% of subjects
Hours of
sleep
Subjects
no. and %
of total sample
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
<4
4-5
5-6
6-7
7-8
8-9
9-10
10-11
11-12
>12
792 (1.3)
875 (1.5)
2530 (4.3)
7741 (13.3)
18 830 (32.3)
16705 (28.7)
6851 (11.8)
2400 (4.1)
955 (1.6)
466 (0.8)
59.4
63.4
70.2
78.3
84.2
84.5
80.0
71.9
58.8
42.9
18.7
18.!
20.2
17.4
13.5
13.3
15.9
20.6
24.2
19.7
14.7
12.3
7.6
3.6
2.0
1.7
3.5
5.4
13.0
14.8
7.2
6.3
2.0
0.7
0.3
0.4
0.7
2.2
4.1
22.7
more than two daily episodes. Among these subjects, 2,933 (35.7% of those reporting
occasional or daily daytime sleep episodes and 5.0% of the total sample) considered
these sleep episodes to affect their lives. As expected, the ratio of complainers increased, respectively, in each of the three groups: 15.6% of those indicating occasional
daytime sleep episodes, 47.4% of those indicating one or two daily daytime sleep episodes, and 59.6% of those reporting more than two daytime sleep episodes.
Related factors in daytime sleep episodes
Hours of sleep (Table 1). Seven to nine hours of sleep were reported by 35,535
subjects, 61 % of the total sample. The percentage of subjects with either occasional or
daily daytime sleep episodes was at its lowest among subjects with 7 -9 h of sleep, and
then increased with either less or more hours of sleep. Some 7.2% of the subjects
sleeping less than 4 hand 22.7% of the subjects sleeping more than 12 h at night reported over 2 daytime sleep episodes per day. Thus, there is a V-shaped relationship
between the number of daytime sleep episodes and the number of reported hours of
sleep per night.
Sleep-wake schedule (Table 2). An irregular sleep-wake schedule was reported by
27,180 subjects (46.7%). The proportion of subjects with daytime sleep episodes was
higher among those on an irregular sleep-wake schedule, and the proportion of sub-
TABLE 2. Sleep-wake schedule and percentages of subjects with no, occasional, one or two,
or more than two daytime sleep episodes (DSE)
% of subjects
Condition
Irregular sleep-wake
schedule
Regular sleep-wake
schedule
Subjects
no. and %
of total sample
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
27 180 (46.7)
75.4
18.2
4.7
1.7
30.982 (53.2)
85.3
12.5
1.8
0.4
Sleep, Vol. 10, No.4, 1987
M. BILLIARD ET AL.
300
TARLE 3. Sleep difficulties and percentages of subjects with no, occasional, one or two, or
more than two daytime sleep episodes (DSE)
% of subjects
SUbjects
no. and %
of total sample
Condition
No sleep difficulty
One sleep difficulty
Two ~ieep difficulties
Three sleep difficulties
34436 (59.1)
14 038 (24.0)
6714 (11.5)
2974 (5)
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
85.7
78.1
67.3
64.5
12.0
17.2
23.6
23.3
1.8
3.8
P
8.9
0.5
0.9
2.4
3.3
jects reporting more than two daytime sleep episodes daily was four times greater
among subjects on an irregular sleep-wake schedule.
Sleep difficulties (Table 3). No sleep difficulty was reported by 34,436 subjects
(59.1%), whereas 23,726 (40.8%) reported one, two, or three sleep difficulties, including delayed sleep onset and/or nocturnal awakf)nings and/or early morning awakening. The fewer sleep difficulties the subjects had, the fewer daytime sleep episodes
they had. The more sleep difficulties they had, the more daytime sleep episodes they
indicated. However, this relation was not linear, and two groups of subjects could be
differentiated: those with no sleep difficulty or only one sleep difficulty, who showed
little impairment of daytime alertness, and those with two or three sleep difficulties,
who showed a clear impairment of their daytime alertness.
Use of hypnotics (Table 4). Of these 17-22-year-old subjects, 2,228 (3.8% of the total
sample) were taking hypnotic drugs daily or almost daily. Of hypnotic users, 20.1% had
one or more daytime sleep episodes per day; 7.1% had more than two daytime sleep
episodes per day, against 3.6% of hypnotic nonusers.
Snoring (Table 5). Habitual snoring was reported by 7,910 subjects, 13.6% of the
total sample. Among these subjects, 31.9% pointed out daytime sleep episodes, either
occasionally (22.5%) or daily (9.4%). In comparison, only 14.1% of non snorers had
occasional daytime sleep episodes, and 3.4% had one or more daytime sleep episodes
per day.
Cataplexy (Table 6). Questions concerning cataplexy were answered by 51,731 subjects; 4,761 (9.2%) gave a positive answer. Among these subjects, 3,047 (5.9% of the
total sample) reported attacks of cataplexy involving head or limbs and 1,714 (3.3% of
the total sample), attacks of cataplexy involving head and limbs. Strikingly enough, the
proportion of subjects with daytime sleep episodes was much higher among those who
TABLE 4. Use of hypnotics and percentages of subjects with no, occasional, one or two, or
more than two daytime sleep episodes (DSE)
% of subjects
Condition
Subjects
no. and %
of total sample
With no
(DSE)
Occasional
(DSE)
lor 2
(DSE)
>2
(DSE)
Users
Nonusers
2228 (3.8)
55 934 (96.1)
55.6
81.7
24.3
14.8
13.0
2.8
7.1
0.8
Sleep, Vol. 10, No.4, 1987
PREVALENCE OF EXCESSIVE SOMNOLENCE
301
TABLE 5. Snoring and percentages of subjects with no, occasional, one or two, or more than
two daytime sleep episodes (DSE)
% of subjects
,.
Condition
Subjects
no. and %
of total sample
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
Habitual snorers
Nonsnorers
7910 (13.6)
50 252 (86.4)
68.2
82.5
22.5
14.1
6.4
2.7
3.0
0.7
reported attacks of cataplexy, and the proportion of subjects with one or several daytime sleep episodes per day was much higher' among the subjects with multifocal cataplexy than among the subjects with unifocal cataplexy.
Role of different factors in excessive daytime somnolence
A stepwise linear discriminant analysis was performed to further examine the different factors of excessive daytime somnolence. The variables entered into analysis
were hours of sleep, irregular sleep/wake schedules, sleep difficulties, use of hypnotics, and snoring. This analysis showed that all five factors were independently related with excessive daytime somnolence. They were ranked as follows: use of hypnotics (p < 10- 5), sleep difficulties (p < 10- 5), irregular sleep-wake schedules (p <
0.001), snoring (p < 0.001), and hours of sleep (p < 0.01).
Groups at high risk for daytime sleep episodes
In addition to the already identified subjects at high risk for daytime sleep episodes
-subjects sleeping less than 5 h or more than 11 h at night, hypnotic users, and subjects reporting attacks of cataplexy (4.1% or more of these subjects indicated more
than two daytime sleep episodes per day)-we looked for subgroups also at high risk
by matching two factors (Table 7). In the first two groups, sleep difficulties/hypnotic
use and snoring/hypnotic use, the percentage of subjects with more than two daytime
sleep episodes did not increase as compared with the group of hypnotic users. This
emphasizes the aforementioned prominence of the hypnotic factor over the other
factors. Additionally, the percentage of subjects with more than two daytime sleep
episodes was slightly increased in the snorers and in the subjects with cataplexy by
adding the sleep difficulty component.
TABLE 6. Attacks of cataplexy and percentages of subjects with no, one or two, or more than
two daytime sleep episodes (DSE)
i~)
I'
I
'"
I
% of subjects
Condition
No cataplexy
Cataplexy involving
face or limbs
Cataplexy involving
face and limbs
Subjects
no. and %
of total sample
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
46970 (90.7)
83.0
14.2
1.9
0.5
3047 (5.9)
56.8
26.3
12.6
4.4
1714 (3.3)
42.9
22.6
21.2
13.3
Sleep, Vol. 10, No.4, 1987
M. BILLIARD ET AL.
302
TARLE 7. Matching of d((ferent factors and percentages of subjects with no, one or two, or
more than two daytime sleep episodes (DSE)
% of subjects
Condition
Sleep difficulties
+ hypnotic use
Snoring + hypnotic use
Snoring + sleep difficulties
Cataplexy + sleep
difficulties
Subjects
no. and %
of total sample
With no
DSE
Occasional
DSE
lor 2
DSE
>2
DSE
2188 (3.7)
3780 (6.5)
4432 (7.6)
55.4
55.6
24.3
21.7
24.6
13.1
13.2
15.1
7.2
3.9
4.8
560 (0.9)
54.9
24.6
13.5
7.0
61.2
DISCUSSION
Methodology
The population chosen for the survey was obviously limited in terms of age and sex,
as it included 17-22-year-old male subjects only. On the other hand, it did not introduce any bias in terms of health, sociocultural level, geographical origin, etc., as it is
mandatory for all French men of this age to go through the selection center. Moreover,
the two selection centers were situated in opposing geographical regions. Thus, this
sample is representative of the 17 - 22-year-old male popUlation in France.
An important methodological issue was to find the best wording of the questions
dealing with excessive daytime somnolence. Due to the difficulty of systematically
expressing what excessive somnolence is, subjects were questioned on the occurrence
of daytime sleep episodes, assuming that excessive somnolence culminates into daytime sleep episodes. Along this line, our results may somewhat underscore the prevalence of excessive daytime somnolence, but in no way do they overscore it. Another
issue was the detection of some subjects with well-defined disorders of excessive somnolence, narcolepsy, idiopathic hypersomnia, psychophysiological hypersomnia, and
hypersomnia with sleep apneas. Due to the impossibility of a thorough investigation of
all subjects reporting daytime sleep episodes in the selection center, a reliable evaluation of the prevalence of these conditions could not be achieved in our sample, but it
was felt that the limited number of subjects with such conditions would not alter our
results concerning the general factors of excessive somnolence.
~
Number of subjects with daytime sleep episodes and number of complainers
The prevalence of subjects with excessive daytime somnolence, as judged by the":
occurrence of daytime sleep episodes, is particularly high. This concurs with the
finding that college students (aged 17-21) are more sleepy than early adolescents and
middle-aged adults (12). This is also consistent with the data from Partinen in a similar
population study of young men prior to military service (9) and from Lugaresi et al.
(10). In distinguishing among subjects with occasional, one or two, and more than two
daily episodes of sleep, our study emphasizes those subjects who may be markedly at
,.
risk for accidents and poor performance. Another point of interest is the striking differ-
Sleep, Vol. 10, No.4. 1987
PREVALENCE OF EXCESSIVE SOMNOLENCE
303
ence between the percentage of subjects reporting occasional or daily daytime sleep
episodes (19%) and the percentage of the subjects actually complaining about these
daytime sleep episodes (5.0%). The reasons for this discrepancy are not clear. However, it is likely that unemployed men, drug addicts, and "night-owls" are not bothered
by their daytime sleep episodes, which allow them to make up for insufficient sleep at
night or to just "kill time."
'!,
'~
'"
'fJ
~J
~'
Related factors in excessive daytime somnolence
One of the fascinating results of this survey is the U-shaped relationship between
daytime sleep episodes and the number of hours of sleep per night. A conventional
number of hours of sleep, i.e., 7-9 h, accompanies a minimum of daytime sleep episodes, whereas less or more hours of sleep go with an increasing number of daytime
sleep episodes. The fact that too little sleep impairs daytime alertness is well documented by studies of sleep restriction (12,13). The relationship between too much sleep
and daytime sleep episodes is less expected. It is common sense that too much sleep
often leads to a type of hangover on awakening, and it was shown that a significant
increase of sleepiness scale ratings occurred 90 min after awakening from a protracted
ad libitum sleep session (14). On the other hand, sleep tendency, measured by the
Multiple Sleep Latency Test, decreases during extension of nocturnal sleep (15). Another possibility is that both excessive hours of sleep at night and daytime episodes are
two different manifestations of an identical pathological process.
The percentage of subjects with an irregular sleep-wake schedule (46.7%) may seem
especially high. There are at least two apparent reasons. The first is that 19-year-old
subjects tend to have irregular bedtimes. The second is that the questionnaire did not
differentiate subjects with a systematically irregular sleep- wake schedule from those
with an irregular sleep-wake schedule on weekends only.
Likewise, the percentage of subjects reporting sleep difficulties (40.8%) is particularly high. However, sleep difficulties have to be clearly differentiated from a complaint of insomnia. In the epidemiological survey of the San Marino population (10),
25-30% of good sleepers less than 35 years of age reported that they needed more than
10 min to fall asleep, and 20% of good sleepers under 20 years of age indicated one or
more awakenings per night. In comparison, only 1.6% of all subjects less than 20 years
of age identified themselves as insomniacs. In the Finnish study (9), only 5.4% of the
respondents were chronically affected with insomnia before entering military service.
In any case, daytime sleep episodes are related with sleep difficulties.
The proportion of subjects taking hypnotic drugs daily or almost daily (3.8% of the
total sample) is more elevated than among young Finnish men before entering military
service (occasional use of hypnotics in 2.5% and frequent or regular use in 0.3%) (9).
The use of hypnotics stands as the primary factor affecting daytime alertness. It is
possible that this negative effect varies with the type of hypnotic(s), but our data do not
allow this distinction to be made. This result stresses the risk of hypnotic use for car
drivers, machinists, army personnel, etc.
The prevalence of habitual snorers in our sample, 13.6%, is intermediate to the
16.8% of men of all ages snoring occasionally (16) and to the 9.5% of Finnish recruits
snoring often or always (9). In the latter study, the snoring question was validated by
the fact that there were practically no nonsnorers among the same subjects questioned
2 years later, when they had returned to civilian life. The impact of snoring on circula-
Sleep, Vol, 10, No, 4, /987
M. BILLIARD ET AL.
304
tory function is a well-documented fact (16-18). Our results stress the deleterious influence of snoring on daytime alertness as well.
As for the prevalence of cataplexy in young adults, our data are in agreement with
those already reported in the literature. The existence of a "Pubertatsnarkolepsie" was
indicated by Redlich and quoted by Wilder (19). Honda, in a census of cataplexy
among teenagers in Fujisawa City (20), found that 23.1% of 8,031 junior high school
students (age range, 12-14 years) and 19.4% of 4,438 senior high school students (age
range 15-16 years) admitted to having experienced cataplexy. Of all respondents in the
Partinen study (9), 16.5% reported occasional weakness in some muscle groups associated with emotional reactions, and 3.7% reported such an experience as frequent or
systematic. Morrison and Dinges (21) administered a "sleep and movement experiences" questionnaire to 707 students (age range 17-24 years), 25% of whom were
experiencing cataplexy under the influence of frightening events, surprise, or laughter.
The additional finding is the strong association between the experience of cataplexy
and daytime sleep episodes, which is in agreement with Partinen's data (9).
CONCLUSION
Unwanted daytime sleep episodes are not unusual in 17-22-year-old men. This study
emphasizes the role of different factors: intake of hypnotics, sleep difficulties, irregular
sleep-wake schedules, snoring, too few or too many hours of sleep, and propensity for
cataplexy. Because of the potential risks of excessive daytime somnolence, in the army
as well as in civilian life, attention of physicians should be directed toward detecting
and preventing this condition.
Acknowledgment: We acknowledge with thanks the French army medical officers, J. Pons, 1.
Dutertre, and 1. Goasguen, who made this study possible. This work was supported by a grant of
the French Ministry of Defense (84~1184IDRET).
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