J Occup Health 2007; 49: 523 527 Journal of Occupational Health Field Study Associations of Excessive Sleepiness on Duty with Sleeping Hours and Number of Days of Overnight Work among Medical Residents in Japan Koji WADA 1, 2, Yumi SAKATA 3, Gilles THERIAULT 2, Rie NARAI 4, Yae YOSHINO 5, Katsutoshi TANAKA 3 and Yoshiharu AIZAWA 1 1 Department of Preventive Medicine and Public Health, Faculty of Medicine, Kitasato University, Japan, 2 Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Canada, 3 Department of Occupational Mental Health, Graduate School of Medical Sciences, Kitasato University, 4 Department of Environmental Health, Faculty of Medicine, University of Occupational and Environmental Health and 5 Department of Nursing System, School of Nursing, Kitasato University, Japan Abstract: Associations of Excessive Sleepiness on Duty with Sleeping Hours and Number of Days of Overnight Work among Medical Residents in Japan: Koji WADA, et al. Department of Preventive Medicine and Public Health, Faculty of Medicine, Kitasato University Despite long-standing concerns regarding the effects of working hours on the performance and health of medical residents, and the patients safety, prior studies have not shown an association of excessive sleepiness with the number of sleeping hours and days of overnight work among medical residents. In August 2005, a questionnaire was mailed to 227 eligible participants at 16 teaching hospitals. The total number of sleeping hours in the last 30 d was estimated from the average number of sleeping hours during regular days and during days with overnight work, and the number of days of overnight work. Multiple logistic regression analysis was used to adjust for potentially associated variables. A total of 149 men and 47 women participated in this study. The participation rate was 86.3%. Among the participants, 55 (28.1%) suffered from excessive sleepiness. Excessive sleepiness was associated with sleeping for less than 150 h in the last 30 d (corrected odds ratio [cor]=1.57; 95% confidence interval [CI], 1.02 2.16). The number of days of overnight work in the last 30 d showed no association with excessive sleepiness. Excessive sleepiness was also associated with smoking (cor, 1.65; 95%CI, 1.01 2.32). Medical residents who slept for less than 150 h in the last 30 d Received Mar 20, 2007; Accepted Aug 8, 2007 Correspondence to: K. Wada, Department of Preventive Medicine and Public Health, Faculty of Medicine, Kitasato University, 1 15 1 Kitasato, Sagamihara-shi, Kanagawa 228-8555, Japan (e-mail: kwada-sgy@umin.ac.jp) and smoked had a significantly higher risk of excessive sleepiness on duty. (J Occup Health 2007; 49: 523 527) Key words: Medical residents, Excessive sleepiness, Sleeping, Overnight Traditionally, medical residents work long hours and do overnight work 1). In the United States and the European Union, legislation restricts the number of hours medical residents are allowed to work 2, 3). There have been intensive arguments on the working hours of medical residents with respect to patients safety, medical residents health and training performance. However, the restriction of working hours has not been shown to improve these factors 4). In Japan, there was no official restriction on the number of hours medical residents can work at the time of the writing of this paper. Sleep deprivation due to overnight work that sometimes exceeds 24 h and the disruption of circadian rhythms have been discussed for a long time 5). Sleep deprivation could be a cause of sleepiness and fatigue, which are common complaints among medical residents 6). The chronic restriction of sleep to less than 6 h per night could be a cause of cognitive performance impairment and could result in medical errors 7, 8). However, most medical residents are unlikely to sleep for more than 6 hours every night since they do overnight work every two to three days. Sleep deprivation and fatigue also impair one s health. They can cause stress, depressive symptoms and somatic complaints 9, 10). Moreover, sleepiness has been linked to higher numbers of traffic accidents involving medical residents 11).
524 J Occup Health, Vol. 49, 2007 Excessive sleepiness is a symptom of sleep disorders 12). It is mainly observed in those with chronic sleep deprivation, sleep apnea syndrome and narcolepsy 13). However, the mechanism of excessive sleepiness is multifactorial 14). Issues related to sleepiness extend beyond working hours and include the full scope of lifestyle conditions and family constraints of medical residents 15). Despite long-standing concerns regarding the effects of working hours on the performance and health of medical residents and the patients safety, prior studies have not shown an association of excessive sleepiness with the number of sleeping hours and days of overnight work. The aim of the present study was to determine the associations of excessive sleepiness on duty with suspected factors such as the total number of sleeping hours and the number of days of overnight work. Methods Participants The participants of this study were medical residents (postgraduate years one and two) who worked in 16 training hospitals located throughout Japan (three in Hokkaido and the Tohoku area, two in the Kanto area, one in the Chubu area, four in the Kansai area and six in the Kyushu area). The hospitals belonged to two major clinical teaching hospital groups. There are 26 teaching hospitals in these two hospital groups. Eight hospitals, which had 3 or fewer medical residents, were excluded from this study and two hospitals did not agree to participate in the study. The participants had been taking a rotation program in various specialties, which included fields such as internal medicine, surgery, pediatrics, emergency medicine, obstetrics and gynecology. Study protocol A questionnaire was distributed to 227 eligible participants (all medical residents of the 16 teaching hospitals) at the end of August 2005 with a letter of invitation explaining the objective and procedure of the study. The purpose of the study was explained to the persons in charge of the survey at each training hospital (the director of the medical residency program). Then, the distribution and collection of questionnaires were performed by the persons in charge of the study. An anonymous self-administered questionnaire was used. Questionnaire The demographic information collected was limited to gender, age, cohabitation, year in the residency program and lifestyles to ensure the anonymity of the respondents and encourage participation. Sleep: The total number of sleeping hours in the last 30 d was estimated as follows: (the average number of sleeping hours during a regular day) (30 d the number of days of overnight work in the last 30 d) + (the average number of sleeping hours during a day with overnight work) (the number of days of overnight work in the last 30 d). The medical residents were allowed to take a nap during overnight work for a couple of hours depending on their duties but they were required to work during daytime even after overnight work. Lifestyle: Lifestyle included smoking and regular physical activity. Current smoking status had two categories: current smokers and non-smokers who included ex-smokers. status also had two categories: more than once a month and none. Excessive sleepiness: Sleepiness was assessed using the following question. During the past month, how often have you had trouble staying awake while working? [excessive sleepiness] (never/less than once a week/once or twice a week/three or more times a week). If the answer to the question was three or more times a week, the participants were considered to suffer from excessive sleepiness. Statistical analysis Chi-square tests were used for analyzing categorical variables. Logistic regression analysis was performed to determine the associations of excessive sleepiness with the total number of sleeping hours in the last 30 d and the number of days of overnight work in the last 30 d. First, those variables were examined by univariate analysis (Model 1). Second, we adjusted for age, gender, cohabitation, smoking and regular physical activity (Model 2). We adjusted for age instead of year of residency program to avoid multi-colinearity. In Model 3, we investigated the association with the number of days of overnight work in the last 30 d adjusting for the same variables as in Model 2. In Model 2 and Model 3, the variables were forced in the model. These adjustments were performed in order to test the independent contribution of the total sleeping hours in the last 30 d and the number of days of overnight work to the risk of excessive sleepiness. All analyses were performed using SPSS 10.0 for Windows 16). Odds ratios were adjusted to corrected odds ratios (cor) according to Zhang s formula 17) to better estimate the actual relative risk, because the prevalence of excessive sleepiness was relatively high. Ethics The Human Research Committee at Kitasato University, Japan approved the recruitment of participants, the obtaining of their consent and the field procedures of this study before the survey was conducted. Results A total of 149 men (mean age ± standard deviation;
Koji WADA, et al.: Excessive Sleepiness among Medical Residents 525 27.5 ± 3.2) and 47 women (mean age ± standard deviation; 26.8 ± 1.7) volunteered to participate in this study. The participation rate was 86.3%. The response rates ranged from 54 to 100% among the hospital sites. The demographic characteristics of the participants are shown in Table 1. Most medical residents did overnight work from 5 to 9 times in the last 30 d. The study participants categorized by excessive sleepiness and several variables are shown in Table 2. Excessive sleepiness on duty was reported by 28.1% (n=55) of the participants. There were more medical residents with excessive sleepiness among those sleeping less than 150 h and among current smokers than among those who slept 150 h or more and among non-smokers. Results of the multiple logistic regression analysis of the associations of excessive sleepiness on duty with the studied variables are shown in Table 3. Model 1 shows the cors analyzed by univariate analysis. There were significant associations of excessive sleepiness with sleeping for less than 150 h in the last 30 d (cor, 1.62; 95% confidence interval [CI], 1.09 2.19) and smoking (cor, 1.65; 95% CI, 1.04 2.30). Model 2 shows significant associations of excessive sleepiness with sleeping for less than 150 h in the last 30 d (cor, 1.57; 95% CI, 1.02 2.16) and smoking (cor, 1.65; 95% CI, 1.01 2.32). The Nagelkerke R-square was 0.1 18). Model 3 shows significant associations of excessive sleepiness with lack of regular physical activity (cor, 1.62; 95% CI, 1.01 2.26) and smoking (cor, 1.71; 95% CI, 1.08 2.37). There was no significant association between the number of days of overnight work and excessive sleepiness. The Nagelkerke R-square was 0.07. Discussion Excessive sleepiness was common among medical residents. In this study, 28.1% of respondents reported excessive sleepiness on duty. Our results indicate that excessive sleepiness is associated not with the number of days of overnight work but the total sleeping hours in the last 30 d. It is also associated with smoking. The most effective remedy for excessive sleepiness is sleeping 13). Sleepiness is inversely related to the number of sleeping hours. The duration of sleep that results in excessive sleepiness is less than 6 h per night in the general Japanese population 19). Medical residents with an average of 5 or less hours of sleep per night calculated from the number of sleeping hours per week were more likely to be involved in serious accidents or injuries 6). Since the sleeping pattern of medical residents varies because of overnight work, we estimated the total sleeping hours in the last 30 d. Sleeping for less than 150 h in the last 30 d can be defined as 5 h of sleep per night and it is significantly associated with excessive sleepiness. Buysse et al. 15) suggested educating medical staff on Table 1. Characteristics of participants n % Total participants 196 Gender Women 47 24.0 Men 149 76.0 Age 24 13 6.6 25 29 150 76.5 30 34 25 12.8 35 39 8 4.1 Year in the residency program First-year 120 61.2 Second-year 76 38.8 50 99 14 7.1 100 149 88 44.9 150 199 87 44.4 200 249 7 3.6 Number of days of overnight work in the last 30 d 0 4 23 11.7 5 9 133 67.9 10 14 36 18.4 15 4 2.0 More than once a month 66 33.7 None 130 66.3 Non-smoker 158 80.6 Smoker 38 19.4 circadian rhythms and the essential role of sleep in maintaining adequate health and performance, because medical residents, attending physicians and hospital administrators do not have enough knowledge about them. Napping is also an effective countermeasure against sleepiness. Napping can significantly enhance alertness and performance during overtime work 20). In this study, no information on napping was available. Previous studies have shown that some lifestyle conditions are also associated with excessive sleepiness. Bixler et al. 14) showed an association between smoking and excessive sleepiness. Lack of physical activity is also weakly associated with excessive sleepiness. In fact, physical activity has some associations with sleep disorders 21). Our study has some limitations. Neither work logs nor diaries were used in assessing working time and sleeping hours. Data are self-reported and retrospective, so we do not know the extent to which these self-reports
526 J Occup Health, Vol. 49, 2007 Table 2. Associations between sleepiness and studied variables among medical residents Without excessive sleepiness With excessive sleepiness n=141 n=55 p-value n (%) n (%) Gender Women 34 (72.3) 13 (27.7) 0.94 Men 107 (71.9) 42 (28.1) Cohabitation Without 115 (72.8) 43 (27.2) 0.69 With 26 (68.4) 12 (31.6) Year in the residency program First-year 84 (70.0) 36 (30.0) 0.52 Second -year 57 (75.0) 19 (25.0) 150 h or more 75 (79.8) 19 (20.2) 0.02 Less than 150 h 66 (64.7) 36 (35.3) More than once a month 52 (78.8) 14 (21.2) 0.14 None 89 (68.5) 41 (31.5) Non-smoker 119 (75.3) 39 (24.7) 0.04 Smoker 22 (57.9) 16 (42.1) Number of days of overnight work in the last 30 d 0 4 16 (69.6) 7 (30.4) 0.85 5 9 98 (73.7) 35 (26.3) 10 14 24 (66.7) 12 (33.3) 15 3 (75.0) 1 (25.0) Table 3. Univariate and multiple logistic regression analyses regarding factors of excessive sleepiness Variables Model 1 Model 2 Model 3 cor 95% CI cor 95% CI cor 95% CI 150 h or more 1.00 1.00 Excluded Less than 150 h 1.62 1.09 2.19 1.57 1.02 2.16 Number of days of overtime 1.01 0.93 1.10 Excluded 1.01 0.93 1.10 work in the last 30 d More than once a month 1.00 1.00 1.00 None 1.51 0.95 2.14 1.55 0.95 2.21 1.62 1.01 2.26 Non-smoker 1.00 1.00 1.00 Smoker 1.65 1.04 2.30 1.65 1.01 2.32 1.71 1.08 2.37 *Model 1: univariate. Model 2 and 3: multivariate analysis adjusted for age, gender, cohabitation, physical activity and smoking. Calculated cor according to Zhang s formula. accurately reflect reality. Moreover, the number of hours of napping and sleeping during daytime and the weekend were not obtained. Further studies should be performed to obtain the number of hours for work and sleep more accurately. Second, even though we had a response rate of 86.3% we do not know if our results are applicable to other medical residents. We did not compare respondents with non-respondents. Third, since this is a crosssectional study, we cannot confirm causal relationships. Despite these limitations, this study provides useful
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