Shoichi 2012_driving_napping_coffee

Contents lists available at SciVerse ScienceDirect j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / s l e e p The factors associated with preferences for napping and drinking coffee ascountermeasures for sleepiness at the wheel among Japanese drivers Shoichi Asaoka, Takashi Abe, Yoko Komada, Yuichi Inoue ⇑ Department of Somnology, Tokyo Medical University, 6-7-1 Nishishinjyuku, Shinjuku-ku, Tokyo 160-0023, JapanJapan Somnology Center, Neuropsychiatric Research Institute, 1-17-7-301 Yoyogi, Shibuya-ku, Tokyo 151-0053, Japan Objective: We explored differences between professional and non-professional drivers in terms of the factors associated with preferences for generally accepted, effective countermeasures for sleepiness at the wheel – i.e., napping and drinking coffee.
Methods: We performed a cross-sectional questionnaire survey. Data from professional (n = 716) and non-professional (n = 3365) drivers were used for analyses.
Results: The results showed that professional drivers experienced drowsy driving and traffic accidents due to falling asleep more often than non-professional drivers. Multiple logistic regression analyses showed that variables which may act as aggravating factors for sleepiness (i.e., engagement in shift-work and insufficient sleep) were associated with preferences for these countermeasures among non- professional drivers. In contrast, among professional drivers, being male and having experienced traffic accidents due to drowsy driving were associated with a preference for napping, while longer annual driv- ing distances and shorter periods after the acquisition of driving licenses were associated with drinking coffee.
Conclusion: Our results suggest that non-professional drivers are likely to take these effective counter-measures when they feel or have the potential to experience sleepiness at the wheel. However, this ten-dency was not observed in professional drivers, and it is speculated that they do not use naps as acountermeasure until they have experienced traffic accidents due to drowsy driving. Sleep educationfor professional drivers and their employers is desirable for preventing drowsy driving-related trafficaccidents.
Ó 2011 Elsevier B.V. All rights reserved.
they are urged to drive for long periods while sleep-deprived andon irregular driving schedules [16,17]. In addition, previous re- Accidents and sleepiness are closely related. Approximately 9– search has shown that sleep apnea syndrome is very prevalent 20% of vehicular accidents are thought to be sleep-related [1]. Pre- among professional drivers [16,18,19]. Together, these factors are vious studies have shown that sleepiness at the wheel caused by thought to make sleepiness at the wheel more prominent in pro- various sleep-related problems, such as insufficient sleep [2–4], fessional drivers, leading to an increased prevalence of drowsy engagement in shift-work [5,6], and sleep disorders [3,7,8], clearly driving and associated traffic accidents [17,20–23].
elevates the risk of drowsy driving and associated traffic accidents.
A number of results from laboratory- and questionnaire-based It has also been shown that drivers’ objective sleepiness, measured epidemiological studies have shown that napping and drinking using maintenance of wakefulness tests or multiple sleep latency coffee are effective countermeasures for drowsy driving [6,24– tests, predict an increased risk of car-accidents and impair driving 28]. Taking a nap as a countermeasure for sleepiness at the wheel performance [9–13]. In addition, accidents caused by drowsy is common among drivers between 46 and 64 years of age, those driving are likely to have disastrous outcomes [1,14], leading to who have already experienced a sleep-related traffic accident, and those who experience severe sleepiness during driving [29].
There are many differences between the driving circumstances It has also been reported that professional drivers [29], especially of professional and non-professional drivers. For example, since long-haul truck drivers [20], tend to nap as a countermeasure for professional drivers are required to deliver their cargo on time, sleepiness. In regard to preference for caffeine ingestion, beingmale, being a professional driver, being over 25 years of age, andhaving experience driving under severe sleepiness were reported to be associated factors [29]. However, differences between E-mail addresses: yuinoue@tokyo-med.ac.jp, inoue@somnology.com (Y. Inoue).
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doi:10.1016/j.sleep.2011.07.020 Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx professional and non-professional drivers in terms of factors asso- awareness of insufficient sleep (yes/no/unknown), a self-rated mea- ciated with preferences for using countermeasures for drowsy sure of daytime sleepiness (Epworth Sleepiness Scale: ESS) [31], driving have not yet been clarified. Clarifying this issue would con- whether another person had noticed loud snoring or apnea in them tribute to promoting awareness among drivers of the appropriate during sleep (yes/no), and the existence of diagnosed sleep disorders countermeasures for sleepiness at the wheel. Therefore, this cross-sectional questionnaire was designed to explore the factorsassociated with preferences for napping and drinking coffee as countermeasures for sleepiness while driving among professionaland non-professional drivers.
For each variable, comparisons were made between the profes- sional and non-professional drivers using a t-test or chi-square test. A t-test was also used to compare the number of countermea-sure categories reportedly used by drivers in the two groups when they became sleepy. Univariate logistic regression analyses wereperformed to explore the factors associated with preferences for This study was part of a research project conducted in the Tokyo napping and drinking coffee, respectively. The variables of ESS, metropolitan area that explored the relationship between sleep BMI, and annual driving distance were categorized dichotomously problems and traffic accidents. It targeted drivers who visited the before being entered into the equation (ESS P11 points [31], BMI Tokyo Metropolitan Driver and Vehicle Licensing Center to acquire P25 kg/m2 [32], and driving distance – the median of annual driv- or renew their driving licenses, and the eligible population in- ing distance of all drivers [5000 km] – respectively). Age was also cluded 12862 drivers who visited the center on weekdays during dichotomized using 25 years of age as a cut-off point, because two weeks in October 2008. Part of the data from this subject pop- younger drivers are at a higher risk of traffic accidents caused by ulation has already been reported by Abe et al. (in press) [30], who falling asleep while driving [33]. The amount of time since a driv- explored the determinant factors for traffic accidents due to ing license was acquired was divided into two almost equal groups drowsy driving. Responses were collected from 8314 drivers who of those with fewer and those with more than 20 years of experi- gave written consent to participate by signing the top page of ence. Next, using the variables that showed significant or nearly the questionnaire. Data from newly licensed drivers (n = 1569), significant associations (including p < 0.10) in the univariate model those who had a driving license for an unknown period of time as the independent variables, multivariate logistic regression anal- (n = 705), and those who did not answer the question about yses (forward selection) were performed. All statistical analyses whether or not they drove professionally (n = 16) were excluded were conducted using SPSS 11.5J (SPSS Japan Inc., Tokyo, Japan).
from the analyses. Data from drivers with an annual driving An alpha level of 0.05 was used as the indicator of statistical distance of 0 km (n = 382) or unknown annual driving distance (n = 1561) were also excluded. Consequently, the followinganalyses are based on data from 4081 drivers (mean age: 42.4 ± 13.4 years; 3021 men, 818 women, 242 of unknown gender;716 professional drivers, 3365 non-professional drivers). This 3.1. Differences in demographic, driving, and sleep-related variables study was approved by the ethics committee of the Neuropsychiat- between professional and non-professional drivers ric Research Institute, Tokyo, Japan.
Larger percentages of professional drivers were male and shift- workers than non-professional drivers (Table 1; % male: 92.5% vs.
75.8%, v = 92.15, p < 0.001; % shift-workers: 27.3% vs. 9.4%, Drivers responded anonymously to items pertaining to accident v = 170.12, p < 0.001). A t-test showed that professional drivers history, socio-demographic variables, driving-related variables, had a higher average BMI than non-professional drivers (22.7 ± and sleep-related variables, including their preferences for counter- 3.3 kg/m2 vs. 23.2 ± 3.3 kg/m2, t[3918] = 3.31, p < 0.001). There measures to cope with sleepiness at the wheel. In this study, the was no significant difference in age between the two groups drivers who answered yes to the question ‘‘Do you drive a car as a (non-professional: 42.34 ± 13.42 years vs. professional: 42.90 ± profession (taxi, bus, or transportation business)?’’ were classified 13.06 years, t[4041] = 1.01, n.s.).
as professional drivers. The drivers were asked whether they used A larger percentage of professional drivers (46.5%) than non- each of a list of countermeasures when they felt sleepiness at the v = 5.46, p < 0.05) reported that their wheel (stopping driving to take a rest, napping, drinking coffee, usual nocturnal sleep duration on weeknights was under six hours.
chewing gum, opening a window, smoking, listening to the radio, Of the professional drivers, 35% reported current awareness of and talking with a passenger, among other measures). The question- insufficient sleep, which was higher than the corresponding per- naire also asked participants to subjectively report the number of centage for non-professional drivers (28.3%, traffic accidents they had been involved in over the past five years There were no differences between the two groups in terms of that were caused by falling asleep (none, one, two, and three or diagnosed sleep disorders and subjective daytime sleepiness, mea- more). Demographic variables included gender, age (years), height sured using ESS (sleep disorders: 2.6 vs. 1.8%, (cm), weight (kg), and engagement in shift-work (yes/no). Driving- 8.57 ± 4.75 vs. 8.53 ± 4.32, t[2853] = 0.19, n.s.). However, the per- related variables included how long they had had a driving license centage of drivers with loud snoring or apnea during sleep was higher for professional drivers than non-professional drivers P30 years), annual driving distance (km), (26.4 vs. 20.2%, v = 13.03, p < 0.001).
frequency of subjective sleepiness while driving (never, occasion- The average annual driving distance was longer for professional ally, sometimes, and usually), and the subjective number of times drivers than non-professional drivers (16141.5 ± 23564.9 vs.
they had experienced drowsy driving during the past year (none, 6610.2 ± 11244.8 km, t[4079] = 16.31, p < 0.001). The percentage once, twice, and three or more times). Sleep-related variables in- of drivers who had their driving licenses for more than 20 years cluded self-reported duration of usual nocturnal sleep on week- was higher for professional drivers (48.9%) than non-professional nights (<6 h, 6 h–<7 h, 7 h–<8 h, 8 h–<9 h, and Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx Table 1Differences between descriptive variables for professional and non-professional drivers.
Demographic variablesGender (% of male drivers) Driving-related variablesPeriod after acquisition of driving license (% of drivers who had licenses for over 20 years) Frequency of occurrence of subjective sleepiness while driving (% of drivers who answered ‘‘sometimes’’ or Experience of drowsy driving during the past year (% of drivers who experienced at least one instance) Experience of traffic accidents caused by falling asleep in the prior five years (% of drivers who experienced at least Sleep variablesUsual nocturnal sleep duration on weeknights (% of drivers who slept fewer than 6 hrs) Current awareness of insufficient sleep (% who said yes) Existence of diagnosed sleep disorders (% who said yes) Existence of loud snoring or apnea during sleep (% who said yes) BMI: body mass index, ESS: Epworth Sleepiness Scale.
* Values are expressed as mean ± SD.
professional drivers reported that they sometimes or usually expe- The most popular countermeasure was to stop driving to take a rienced sleepiness while driving, and this rate was significantly rest, reportedly used by more than 40% of the drivers in both groups higher than the rate for non-professional drivers (20.2%, (Fig. 1). The percentage of drivers who used napping as a counter- v = 41.03, p < 0.001). The percentage of drivers who reported expe- measure was 20.4% for professional and 18.5% for non-professional riencing drowsy driving at least once in the preceding year was also drivers. Drinking coffee was reported to be used as a countermea- higher among professional than non-professional drivers (profes- sure by 30% of non-professional and 27.7% of professional drivers.
Between the groups, there were no significant differences in the addition, 3.5% of the professional and 1.2% of the non-professional drivers reported experiencing traffic accidents due to falling asleep v = 1.40, n.s.) as countermeasures. Chewing gum, opening a while driving during the preceding five years; the rate for profes- window, and talking with passengers were preferred by non-profes- sional drivers was significantly higher than that for non-professional sional drivers more than professional drivers ( 2 v = 4.79, p < 0.05; v = 33.53, p < 0.001, respectively). On the otherhand, smoking was more widely preferred by professional than non-professional drivers ( 2 v = 10.89, p < 0.01). Between professional and 3.2. Countermeasures for sleepiness at the wheel non-professional drivers, there were no differences in rates of listen-ing to the radio or the use of other kinds of countermeasures (listen- The percentage of drivers who used at least one kind of counter- v = 0.92, n.s.; others: v = 1.61, n.s.).
measure when they felt sleepy at the wheel was higher for non-professional (77.7%) than professional (70.9%) drivers ( 2 p < 0.001). A t-test showed that non-professional drivers used a 3.3. Factors associated with preference for napping significantly larger number of countermeasures than professionaldrivers (2.08 ± 1.82 vs. 1.87 ± 1.88 categories; t[4079] = 2.79, The univariate logistic regression analysis showed that being male, being a shift-worker, having current awareness of insuffi- Fig. 1. Comparison of the percentages of drivers who use different countermeasures when they feel sleepy at the wheel. ⁄⁄p < 0.01, ⁄p < 0.05 (chi-square test) betweenprofessional and non-professional drivers. Participants were allowed to choose multiple countermeasures.
Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx Table 2Results of logistic regression analyses of factors associated with napping as a countermeasure among non-professional drivers.
Loud snoring and respiratory pauses during sleep Experience of traffic accidents caused by falling asleep Usual nocturnal sleep duration on weeknights (hours) Frequency of subjective sleepiness while driving Period after acquisition of driving license (years) CI: confidence interval, ref: reference category, BMI: body mass index, ESS: Epworth sleepiness scale.
cient sleep, experiencing drowsy driving, having higher BMI, driv- an awareness of insufficient sleep, and having gone through a per- ing longer annual distances, sleeping fewer than six hours on usual iod of fewer than 20 years following acquisition of driver’s license weeknights, frequently experiencing subjective sleepiness while were factors associated with drinking coffee as a countermeasure driving, and having shorter driving histories were all associated with a preference for napping among non-professional drivers.
In regard to professional drivers, the variables that showed sig- The multivariate logistic regression analysis revealed that fre- nificant association with a preference of drinking coffee in univar- quency of subjective sleepiness while driving, being male, being iate logistic regression analysis were longer annual driving a shift-worker, having longer annual driving mileage, and having distance (>5000 km/year), shorter period after acquisition of driv- shorter driving history were significantly associated with using ing license (3–20 years), and younger age (625 years). The multi- napping as a countermeasure (Table 2).
variate logistic regression model also showed a significant As for professional drivers, univariate logistic regression analy- association between the former two variables and a preference sis revealed that being male, being a shift-worker, driving longer annual distances, experiencing traffic accidents caused by fallingasleep, and having shorter driving histories were significantly asso-ciated with a preference for napping as a countermeasure for sleepiness. However, the results of the multivariate logistic regres-sion analysis revealed that napping was only associated with being The results of this study show traffic accidents caused by falling male and experiencing traffic accidents caused by falling asleep asleep to be more common among professional than non-profes- sional drivers. In addition, a larger proportion of professional driv-ers were likely to experience drowsy driving and reported frequent 3.4. Factors associated with preference for drinking coffee experiences of sleepiness while driving. These results are compat-ible with previous studies that have reported a high incidence of The univariate logistic regression analysis of the data from non- sleep-related accidents [34] and frequent sleepiness at the wheel professional drivers showed that being younger (625 years), being a shift-worker, having current awareness of insufficient sleep, In this study, the annual driving distance was longer and the experiencing traffic accidents by falling asleep, sleeping fewer than number of shift-workers was higher among professional drivers six hours on usual weeknights, and having had a driver’s license for than non-professional drivers. Many previous studies have shown a shorter period of time (3–20 years) were associated with a pref- that long-haul and nighttime driving elevates the risk of sleepiness erence for drinking coffee among non-professional drivers while driving and the risk of sleep-related traffic accidents [1,6,35].
(Table 4). The multivariate logistic regression analysis revealed These are common driving conditions for professional drivers and, that, in non-professional drivers, engaging in shift-work, having thus, causative of the frequent occurrence of sleepiness while driv- Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx Table 3Results of logistic regression analyses of factors associated with napping as a countermeasure among professional drivers.
Loud snoring and respiratory pauses during sleep Experience of traffic accidents caused by falling asleep Usual nocturnal sleep duration on weeknights (hours) Frequency of subjective sleepiness while driving Period after acquisition of driving license (years) CI: confidence interval, ref: reference category, BMI: body mass index, ESS: Epworth sleepiness scale.
Table 4Results of logistic regression analyses of factors associated with drinking coffee as a countermeasure among non-professional drivers.
Loud snoring and respiratory pauses during sleep Experience of traffic accidents caused by falling asleep Usual nocturnal sleep duration on weeknights (hours) Frequency of subjective sleepiness while driving Period after acquisition of driving license (years) CI: confidence interval, ref: reference category, BMI: body mass index, ESS: Epworth sleepiness scale.
Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx Table 5Results of logistic regression analyses of factors associated with drinking coffee as a countermeasure among professional drivers.
Loud snoring and respiratory pauses during sleep Experience of traffic accidents caused by falling asleep Usual nocturnal sleep duration on weeknights (hours) Frequency of subjective sleepiness while driving Period after acquisition of driving license (years) CI: confidence interval, ref: reference category, BMI: body mass index, ESS: Epworth Sleepiness Scale.
ing, drowsy driving, and of sleep-related traffic accidents among there are no significant differences in the ESS score of the two this population. In addition, as shown in previous studies [3,17], groups. However, further study is needed to clarify the inconsis- shorter habitual sleep time and current awareness of insufficient tency between the result of ESS and the frequency of the occur- sleep were common among professional drivers. Such poor sleep rence of subjective sleepiness while driving.
habits could also play a role in increasing sleepiness at the wheel Although a larger proportion of professional drivers reported frequent sleepiness while driving than non-professional drivers, The existence of sleep disorders, especially obstructive sleep ap- the results of our study showed that professional drivers used few- nea syndrome, also increases the risk of drowsy driving [7,15].
er countermeasures. Specifically, the percentages of professional Although previous studies reported a high prevalence of obstruc- drivers who reported chewing gum, opening a window, and talking tive sleep apnea syndrome in professional drivers [16,18,19], no with passengers as countermeasures were lower than the corre- difference was found in this study between the percentage of pro- sponding rates for non-professional drivers. On the other hand, fessional drivers who had been diagnosed with sleep disorders and there were no differences in preferences for countermeasures the percentage of non-professional drivers diagnosed. However, known to be effective – that is, napping and drinking coffee [24].
BMI and the percentage of drivers who had loud snoring or apnea In this study, about 20% of drivers in both groups reported napping during sleep were higher among professional than non-profes- as a countermeasure for sleepiness at the wheel; this was lower sional drivers. Since obesity and snoring are core characteristics than the percentage of drivers who reportedly stopped driving to of obstructive sleep apnea syndrome and are used as reliable rest, drank coffee, chewed gum, and opened windows as counter- screening items for the syndrome [36–38], more professional than measures. This finding is notably consistent with the results of An- non-professional drivers may have undiagnosed sleep apnea, pos- und et al. (2008), which showed that napping was not the first sibly contributing to the elevated levels of sleepiness at the wheel choice to reduce sleepiness at the wheel. They reported that nap- ping and caffeine ingestion were used as countermeasures more The mean ESS score of professional drivers did not significantly frequently by professional than non-professional drivers [29].
differ from that of non-professional drivers, despite the profes- However, this tendency was not confirmed by this study.
sional group’s larger proportion of shift-workers and drivers with Notably, the results of this study revealed that factors associ- potential sleep apnea and shorter usual sleep times. These results ated with preferences for napping and drinking coffee as counter- may suggest that professional drivers are likely to underestimate measures for sleepiness at the wheel differed between professional their sleepiness in daily settings. Previous studies have shown that and non-professional drivers. For non-professionals, the preference cumulative sleep loss leads to underestimation of subjective sleep- for napping was associated with male drivers, frequency of subjec- iness [39], and that the ESS score cannot correctly gauge partici- tive sleepiness while driving, and the existence of conditions that pants’ sleepiness, especially among shift-work drivers with sleep could cause increased sleepiness while driving (i.e., shift-work, apnea syndrome [40]. These phenomena may partly explain why long driving distances). In addition to a preference for drinking cof- Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020 S. Asaoka et al. / Sleep Medicine xxx (2012) xxx–xxx fee, engagement in shift-work and awareness of insufficient sleep survey with a retrospective design, detailed causal relationships also appeared as associated factors. These results could indicate between preferences for countermeasures and accidents could that non-professional drivers are likely to nap or drink coffee in sit- uations in which sleepiness could be elevated.
In conclusion, among the drivers surveyed for this study, nap- For professional drivers, long annual driving distances and ping was not a common countermeasure for coping with sleepi- shorter periods following the acquisition of driving licenses ness at the wheel. In particular, professional drivers who had not showed significant association with preference of drinking coffee; experienced traffic accidents due to falling asleep seemed hesitant however, no other sleepiness-related variables appeared as the to nap when they felt sleepy. In addition, they did not tend to drink associated factor for this countermeasure. This result may suggest coffee even when they were in driving situations in which sleepi- that, in contrast to non-professional drivers, professional drivers ness was likely to increase. Many previous experimental and inter- do not tend to drink coffee in situations where sleepiness could vention studies showed that these countermeasures decrease be elevated. In addition, preference for napping was only associ- drivers’ sleepiness and improve their driving performance ated with being male and experiencing a traffic accident due to [24,26–28]. Therefore, it should be emphasized that using counter- drowsy driving, which suggests that professional drivers often measures can contribute to decreased sleepiness at the wheel and avoid napping until they have experienced a sleep-related vehicu- possibly reduces the risk of sleepiness-related traffic accidents.
lar accident. As mentioned above, in contrast to the results of pre- Professional drivers and their employers (e.g., transportation com- vious studies conducted in western countries [29], no difference panies) should be educated about the importance of napping and was found between the rates of professional and non-professional drinking coffee to cope with sleepiness at the wheel, as this could drivers who take naps as countermeasures in this study. This may be because the driving situations of Japanese professional driversmake it difficult for them to nap during work time. Further re- search is needed to explore the relationship between a preferencefor napping and driving conditions. Alternately, it is also possible The ICMJE Uniform Disclosure Form for Potential Conflict of that fewer drivers in Japan have knowledge of the efficiency of this Interest associated with this article can be viewed by clicking on countermeasure than those in western countries. Notably, the the following link: doi:10.1016/j.sleep.2011.07.020.
present study shows that both professional and non-professionaldrivers with more experience tend to hesitate to use these counter-measures. This may imply that more experienced drivers are likelyto underestimate the deterioration of their driving performance due to sleepiness, or underestimate the effects of countermeasures.
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Please cite this article in press as: Asaoka S et al. The factors associated with preferences for napping and drinking coffee as countermeasures for sleepinessat the wheel among Japanese drivers. Sleep Med (2012), doi:10.1016/j.sleep.2011.07.020

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