Excessive daytime sleepiness and the problem of its definition

The main problem encountered in the study of excessive daytime sleepiness is the lack of uniformity in the definition of excessive daytime sleepiness (see Table).

One series of epidemiological inquiries, essentially North American, focused on hypersomnia symptoms, such as getting too much sleep or napping. On the other hand, European studies assessed daytime sleepiness and sleep propensity in situations of diminished attention. Consequently, the variance in results across studies does not make it possible to reach a definite conclusions in the matter.

The four U.S. studies that investigated hypersomnia reported rates varying from 0.3% to 16.3%:

  • Bixler et al. (14) simply mentioned they assessed hypersomnia and reported a prevalence of 4.2%.
  • In the Ford and Kamerow study (35), participants were asked whether they had gone a period of two weeks or more in which they slept too much (hypersomnia). This yielded a 6-month prevalence of hypersomnia of 3.2%.
  • Using the same definition, Breslau et al. (20) found a lifetime prevalence of hypersomnia of 16.3% in their young adult sample (21 to 30 years of age).
  • Klink and Quan (69) examined how many participants fell asleep during the day and found an overall prevalence of 12%.
  • The Cardiovascular Health Study (148) found a 20% prevalence of participants being "usually sleepy in the daytime" in a sample of 4578 adults aged 65 and older.

In a Mexican study (140), 9.5% of the sample claimed to get too much sleep, and 21.5% claimed to experience a strong need to sleep during the day.

A Brazilian community study (135) used the Epworth Sleepiness Scale to measure excessive daytime sleepiness in a sample of 408 adults from Campo Grande city. They found a prevalence of 18.9%.

In Europe, the Swedish study by Gislason and Almqvist (39) yielded a prevalence rate of 16.7% for moderate daytime sleepiness and of 5.7% for severe daytime sleepiness in their male sample.

Janson et al. (59) found a prevalence of daytime sleepiness occurring at least one day per week of about 40%; daily daytime sleepiness was observed in about 5% of their young adult sample (20 to 44 years of age) drawn from three different countries.

Martikainen et al. (83), who used a more restrictive definition of excessive daytime sleepiness, found that 9.8% of their 1,190 Finnish respondents aged 36 to 50 years reported being "clearly more tired than others", experiencing a "daily desire to sleep in the course of normal activities", or feeling "very tired daily".

Hublin et al. (52) found a prevalence of daytime sleepiness occurring daily or almost daily of 9% in their Finnish twin cohort.

Ohayon et al. (95) assessed daytime sleepiness on a severity scale in their UK sample of 4,972 subjects. Severe daytime sleepiness was observed in 5.5% of their sample, and moderate daytime sleepiness in 15.2%. A Northern Irish community study (89) involving 2,364 aged between 18 ad 91 years reported a prevalence of 19.8% of moderate or severe excessive daytime sleepiness.

Two epidemiological studies have linked excessive daytime sleepiness to cognitive deficits:

  • In a study involving 2,346 Japanese-American men aged between 71 and 93 years, Foley et al. (32) found that men who reported excessive daytime sleepiness at baseline were twice as likely to be diagnosed with dementia three years later than those without daytime sleepiness.
  • In another study involving 1026 subjects aged 60 years or older, Ohayon and Vechierrini (109) found that, after controlling for age, gender, physical activity, occupation, organic diseases, use of sleep or anxiety medication, sleep duration and psychological well-being, subjects with excessive daytime sleepiness were twice as likely to have attention-concentration deficits, difficulties in orientation and memory problems than did the others.

Unlike insomnia symptoms, excessive daytime sleepiness is generally not gender-related.

Whether its prevalence increases or decreases with age is not clear, as both trends have been observed (39,69).

Excessive daytime sleepiness can be caused by various factors such as poor sleep hygiene (52,95), work conditions (95), and psychotropic medication use (52,95).

Excessive daytime sleepiness has been found to be associated also with:

  • sleep-disordered breathing (52, 59, 95)
  • psychiatric disorders, especially depression (20, 35, 45, 52, 95)
  • physical illnesses (59, 95)

Prevalence of excessive sleepiness in the general population of America and Western Europe countries
Authors N Age Sample selection Type of interview Description Prevalence (%)(M/F)
Karacan et al.
Alachua county, Florida, USA, 1976
1645 ≥ 18 Random sample Household Hypersomnia 0.3
Bixler et al.
Los Angeles, USA, 1979
1006 ≥ 18 Random stratified sample Household Sleep too much 4.2
Klink & Quan
Tucson, USA, 1987
2187 ≥ 18 Random stratified sample Self-administrated questionnaire Falling asleep during the day 12.3/11.7
Ford & Kamerow
Baltimore, Durham, Los Angeles, USA, 1989
7954 ≥ 18 Household probability sample Household Sleep too much lasting 2 weeks or more, and professional consultation, sleep enhancing medication intake, or interfere a lot with daily life 2.8/3.5
Tellez-Lopez et al.
Monterrey, Mexico, 1995
1000 ≥ 18 Not specified Household Getting too much sleep
Strong need to sleep in the day
Hays et al
North Carolina, USA, 1996
3962 ≥ 65 Random sample Household Frequent feeling of sleepiness during the day or evening that need to take a nap 25.2
Lugaresi et al.
San Marino, Italy, 1983
5713 ≥ 3 Representative sample Household Sleepiness independant of meal times 8.7
Gislason & Almqvist
Uppsala, Sweden, 1987
3201 men 30-69 Random sample Postal questionnaire Moderate daytime sleepiness
Severe daytime sleepiness
Liljenberg et al.
Gavleborg & Kopparberg counties, Sweden, 1988
3557 30-65 Random sample Postal questionnaire Daytime sleepiness often or very often 5.2/5.5
Martikainen et al [54]
Tampere, Finland, 1992
1190 36-50 Random stratified sample Postal questionnaire - Considered themselves more clearly tired than others, or
-Daily experience of desire to sleep during normal activities, or
- Felt tired every day
Hublin et al.
Finland, 1996
11354 33-60 Twin cohort Postal questionnaire Daytime sleepiness every or almost every day 6.7/11.0
Janson et al.
Reykjavik, Iceland
Uppsala & Goteborg, Sweden, Antwerp, Belgium, 1995
2202 20-45 2 phases:
1) Random sample of the gen. pop.
2) Random sample of the phase 1 responders
1) Postal questionnaire
2) structured interview + Self-administrated
Daytime sleepiness ≥3 days/week 11-21
Enright et al.
Forsyth, Sacramento, Washington, Pitttsburg counties, USA, 1996
5201 ≥ 65 Random sample of the Health Care Finance Administration Medicare eligibility lists Self-administrated questionnaire + clinical examination Being usually sleepy in the daytime 17.0/15.0
Vasterbotten & Norrbotten, Sweden, 1996
6143 ≥ 65 None Postal questionnaire - Often sleepy during the day
- Often naps in daytime
Ohayon et al
United Kingdom
4972 ≥ 15 2 stages:
1) Random stratified sample
2) Household probability sample
Telephone Feel sleepy during the day:
A lot or greatly, ≥ 1 month
Moderately, ≥ 1 month