Environmental Tobacco Smoke Exposure and Overtime Work as Risk Factors for Sick Building Syndrome in Japan
Tetsuya Mizoue1,
Kari Reijula2 and
Kjell Andersson3
1 Department of Clinical Epidemiology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu, Japan.
2 Finnish Institute of Occupational Health, Helsinki, Finland.
3 Department of Occupational and Environmental Medicine, Örebro Medical Center Hospital, Örebro, Sweden.
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ABSTRACT
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Sick building syndrome (SBS) is an increasingly common health problem for workers in modern office buildings. It is characterized by irritation of mucous membranes and the skin and general malaise. The impact of environmental tobacco smoke (ETS) exposure and overtime work on these symptoms remains unclear. The authors examined these relations using data from a 1998 cross-sectional survey of 1,281 municipal employees who worked in a variety of buildings in a Japanese city. Logistic regression was used to estimate the odds ratio for symptoms typical of SBS while adjusting for potential confounders. Among nonsmokers, the odds ratio for the association between study-defined SBS and 4 hours of ETS exposure per day was 2.7 (95% confidence interval: 1.6, 4.8), and for most symptom categories, odds ratios increased with increasing hours of ETS exposure. Working overtime for 30 or more hours per month was also associated with SBS symptoms, but the crude odds ratio of 3.0 for SBS (95% confidence interval: 1.8, 5.0) was reduced by 21% after adjustment for variables associated with overtime work and by 49% after further adjustment for perceived work overload. These results suggest that both ETS exposure and extensive amounts of overtime work contribute to the development of SBS symptoms and that the association between overtime and SBS can be explained substantially by the work environment and personal lifestyle correlated with overtime.
cross-sectional studies; occupational exposure; overtime; sick building syndrome; tobacco smoke pollution; workload
Abbreviations:
CI, confidence interval; ETS, environmental tobacco smoke; OR, odds ratio; SBS, sick building syndrome
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INTRODUCTION
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Sick building syndrome (SBS), which is characterized by irritation of mucous membranes and the skin and general malaise (1
), is an increasingly common health problem for workers in modern office buildings (2


6
). Factors affecting indoor air quality, such as type of ventilation (2
, 3
, 6
), have been linked to symptoms typical of SBS, being modified by physical and psychological work environments and personal factors (4
, 5
, 7
, 8
). The impact of a particular risk factor on the development of SBS may vary among different settings according to the relative importance of each factor.
Among Japanese employees, special attention has been paid to environmental tobacco smoke (ETS) exposure and long working hours, both of which are potential hazards to health. First, since over half of Japanese adult men smoke (9
), ETS would be expected to be a major source of indoor air contaminants in workplaces with limited smoking restrictions, and it may reach a level that has unfavorable effects on nonsmokers' health (10
). However, since epidemiologic evidence linking SBS symptoms to ETS exposure is limited (11
, 12
), ETS has been considered a minor contributor to the occurrence of SBS (13
). Second, the mean number of working hours per year in Japan is the second greatest among developed countries, after the United States (14
), and studies have revealed that working extended hours is a cause of chronic diseases (15
17
). Working long hours may increase the risk of SBS because of long periods of exposure to indoor air contaminants, or it may operate through related causative factors for SBS, such as prolonged use of video display terminals (4
, 5
, 7
), psychological stress (4
, 5
, 7
, 8
), or deterioration of quality of life.
Therefore, we examined the relation of the above two working conditions with symptoms typical of SBS, using cross-sectional data on municipal employees in Kitakyushu, Japan. For the relation between overtime and SBS symptoms, we also evaluated the extent (if any) to which the association was explained by factors concomitant with working additional hours.
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MATERIALS AND METHODS
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Survey
A health survey was conducted among municipal employees of a city agency in Kitakyushu. The survey had two primary aims: to examine workers' attitudes toward workplace smoking restrictions and to investigate the relation between working conditions and SBS. A previous report on the former topic provided details on the study procedure (18
). Briefly, in January 1998, one third of the municipal employees from a city agency in the northeastern part of Kyushu Island, Japan, were randomly selected and asked to answer an anonymous questionnaire on work and health. The questionnaire included queries on working conditions, perceived work stress, and health-related lifestyle factors, as well as SBS symptoms. A response rate of 89 percent (n = 2,847) was obtained.
The city agency surveyed consists of one main building, several secondary buildings, and satellite offices. Periodic measurement indicated no serious problem regarding indoor air in the main building or the secondary buildings, but no such measurement was obtained for the satellite offices. The windows of the main building do not open, but those of the other buildings do. The main building and some of the secondary buildings are mechanically ventilated and air-conditioned, and both systems were in use during the survey period. Smoking in the workplace is not restricted by law in Japan, but the city agency under study had restrictive policies on smoking at the time of the survey, with varying intensities of restriction across workplaces (18
). As in other offices in Japan, most subjects worked together in unpartitioned rooms.
SBS symptoms
Questions on symptoms of SBS were derived from the Miljömedicin 040 questionnaire, English version A (MM040EA), a validated self-administered questionnaire designed for epidemiologic assessment of indoor air problems (19
). Symptoms surveyed, for the preceding 3-month period, were as follows: fatigue; feeling heavy-headed; headache; nausea/dizziness; difficulty concentrating; itching, burning, or irritation of the eyes; irritated, stuffy, or runny nose; hoarse, dry throat; cough; dry or flushed facial skin; scaling/itching of the scalp or ears; and dry, itching, or red-skinned hands. For each symptom, the following answers were possible: "Yes, often (every week)"; "Yes, sometimes"; and "No, never." An additional query concerning the attribution of a symptom to the work environment, included in the original questionnaire, was not used in the present study. The test-retest reliability for single-symptom questions, measured as kappa values, varied from 0.31 to 0.59 (mean = 0.45) (20
). One of the present authors translated the English version of the questionnaire into Japanese for this study.
A symptom that occurred often (weekly) was defined as positive. For the analysis, symptoms were categorized by anatomic site: general symptoms (fatigue; feeling heavy-headed; headache; nausea/dizziness; having difficulty concentrating); symptoms involving the eyes, nose, and throat (including cough); and symptoms involving the skin. A subject who had at least one positive symptom for an anatomic site was designated positive for that site. For this study, a respondent was considered positive for SBS if he or she reported at least one general symptom and at least one symptom regarding the eyes, nose, throat, or skin. These symptoms did not completely satisfy the conventional definition of SBS in that we could not exclude symptoms arising from a specific disease or from nonoffice factors, because of a lack of information on the occurrence of each symptom.
ETS, overtime, and covariates
For daily hours of workplace exposure to ETS during the previous month ("How many hours per day do you work in an indoor workplace where cigarette smoke is present?"), there were four response options: never, <1 hour, 1 hour<4 hours, and
4 hours. Regarding total hours of overtime work during the preceding 1-month period, there were four response options: none or <10 hours, 10<30 hours, 30<60 hours, and
60 hours. The first two response categories for ETS exposure were combined to make a reference group, and the last two categories for overtime were combined.
Factors consistently cited as risk factors for SBS or those that may accompany overtime were considered as potentially confounding factors. Included in the analyses were age (<35 years, 35<45 years, or
45 years), sex (male, female), type of building (secondary building, satellite building, or main building), position (staff, sectional subchief, or higher), history of asthma or hay fever (no, yes), daily hours of video display terminal use (none, <1 hour, 1<4 hours, or
4 hours), interest in one's work (sometimes/often, never/seldom), work overload (never/seldom/sometimes, often), control over one's work (sometimes/often, never/seldom), support from colleagues (sometimes/often, never/seldom), distress over interpersonal relations at work (never/seldom/sometimes, often), participation in sports activity (none/less than three times per week, three or more times per week), and usual amount of sleep (
6 hours per night, <6 hours per night), as well as ETS exposure and overtime. Work overload, which was highly correlated with overtime (table 1), was also treated as an exposure for the comparison of the effects of these factors on SBS symptoms.
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TABLE 1. Characteristics (%) of 1,281 municipal workers according to amount of overtime worked during the previous month, Kitakyushu, Japan, 1998
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Statistical analysis
We excluded 1,279 employees who did not work mainly indoors and an additional 287 who had missing data on any of the variables, which left 1,281 for the present analysis. Differences in proportions across categories of overtime were assessed by chi-squared test. The relations of exposure to outcomes, the five categories of SBS symptoms and study-defined SBS, were assessed independently in separate models. Multivariate logistic regression was used to estimate the odds ratio for each outcome and its 95 percent confidence interval, with adjustment for the above-mentioned variables. An indicator term for current smoking irrespective of ETS exposure was added simultaneously with the terms for ETS exposure specific to nonsmokers. Overtime and work overload were first assessed in separate models: Work overload was not included in the model for overtime and vice versa. Next, to determine the extent of risk crudely associated with overtime but due to other factors related to overtime, we calculated a crude odds ratio for 30 or more hours of overtime, with adjustment for age, sex, type of building, position, and history of asthma or hay feverfactors that are constant even if overtime changes. Then we estimated an adjusted odds ratio by adding to this model each of the other variables one by one, all variables except work overload simultaneously, and all variables including work overload. The percentage change in the odds ratio (OR) was expressed by the following equation: % change = (adjusted OR - crude OR)/(crude OR - 1) x 100. All analyses were performed using SAS software (21
).
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RESULTS
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Subjects who had worked overtime for 30 or more hours during the past month were more likely to be male, to be young, to hold a lower-level position, to be assigned to the main building, and to have a history of asthma or hay fever compared with subjects with less than 10 hours of overtime work (table 1). Such employees tended to work with video display terminals and were exposed to ETS longer than employees with fewer hours of overtime work. Over half of the nonsmokers were exposed to workplace ETS for 4 or more hours per day. Overtime was highly correlated with work overload. Extensive overtime was nonsignificantly associated with low levels of control over one's work and high levels of distress over human relations in the workplace. Subjects who had worked more overtime were less likely to engage in regular sports activities and had fewer hours of sleep per night.
As table 2 shows, a clear trend association was observed between hours of ETS exposure and SBS symptoms among nonsmokers; the odds ratio was significantly elevated for workers with the greatest amount of ETS exposure (for SBS, OR = 2.7, 95 percent confidence interval (CI): 1.6, 4.8). Odds ratios were relatively high for symptoms pertaining to the nose, throat, and eyes. A similar finding was obtained when analysis was limited to subjects who worked in the main building (data not shown). Subjects in workplaces with strict restrictions on smoking, such as a total ban or a workroom ban, had reduced odds ratios for symptoms of the nose (OR = 0.5, 95 percent CI: 0.3, 0.9), throat (OR = 0.6, 95 percent CI: 0.4, 1.0), and skin (OR = 0.6, 95 percent CI: 0.3, 1.0) compared with subjects in workplaces with milder restrictions. Among current smokers, odds ratios for SBS symptoms neither increased (table 2) nor showed a trend association with hours of ETS exposure (data not shown) when nonsmokers who were not exposed to workplace ETS were used as the reference group.
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TABLE 2. Results from multivariate logistic regression analysis of the association between workplace exposure to environmental tobacco smoke and symptoms typical of sick building syndrome in 1,281 municipal workers, Kitakyushu, Japan, 1998
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As table 3 shows, working overtime for 30 or more hours per month as compared with less than 10 hours was associated with self-reported SBS and with both general symptoms and skin-related symptoms. Perceived work overload was also associated with SBS; odds ratios for the highest category of work overload were increased to the same extent as those for working 30 or more hours of overtime per month. Adjustment for all variables except work overload and full adjustment including work overload reduced the crude SBS odds ratio of 2.96 (95 percent CI: 1.77, 4.95) for workers with long overtime by 21 percent and 49 percent, respectively (table 4).
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TABLE 3. Results from multivariate logistic regression analysis of the association between working overtime and perceived work overload and symptoms typical of sick building syndrome in 1,281 municipal workers, Kitakyushu, Japan, 1998
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TABLE 4. Odds ratios for symptoms of sick building syndrome* among municipal employees who worked overtime for 30 hours per month, and percent change from the crude odds ratio after inclusion of variables associated with overtime (n = 1,281), Kitakyushu, Japan, 1998
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DISCUSSION
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The present study examined the relations of ETS and overtime work to SBS symptoms among Japanese municipal employees with a high prevalence of ETS exposure in the workplace. The results suggested that both ETS exposure and extensive overtime work are determinants of SBS symptoms. However, a combination of occupational and lifestyle factors associated with working overtime explained a substantial proportion of the crude relation between overtime and SBS symptoms.
ETS exposure
ETS is a dynamic, complex mixture of thousands of compounds, including numerous irritants, and it causes some acute symptoms typical of SBS, such as irritation of the eyes, nose, and throat (22
). Our findings suggest that ETS exposure is a major determinant of SBS in a working population with a high prevalence of smoking and few workplace smoking restrictions. This is consistent with a previous study that showed a markedly reduced prevalence of symptoms of sensory irritation among bartenders after restrictions on smoking in bars were imposed (23
). It may be possible to generalize the present result to workplaces with similar conditions. In workplaces that have strict rules on smoking, ETS may be reduced to levels that do not significantly contribute to the occurrence of SBS.
Overtime work
The results of this study are consistent with a previous finding indicating an increased risk of SBS among employees with long working hours (8
) or unfavorable psychosocial conditions (4
, 5
, 7
, 8
). As expected, the association was strongest for the general symptom category including fatigue and headache, but an elevated risk was also noted for some other categories of SBS symptoms. A plausible explanation for the independent association is that workers who spend more time in the workplace are exposed to indoor air contaminants over longer periods. Other possible mechanisms include increased susceptibility to indoor climates resulting from changes in the function of the autonomic system (24
).
We estimated the extent of the crude association between overtime work and SBS that could be explained by factors concomitant with overtime. The odds ratio for SBS in subjects who worked extensive amounts of overtime was substantially reduced after adjustment for work overload. Since extensive overtime would be expected to lead to a perception of work overload, this finding indicates that overtime increases risk of SBS largely by affecting perceptions of work overload. However, it is not easy to interpret the reduction in the odds ratio for other covariates, whose relation to overtime may be causal, confounding, or both. For instance, working overtime may cause a deterioration in quality of life, heightening the risk of SBS through this pathway. At the same time, it is possible that overtime is noncausally associated with an unhealthy lifestyle. This could be possible for any of the covariates in the present study. Accordingly, we can only state that some part of the crude association between overtime work and SBS was attributable to the causal and noncausal effects of factors concomitant with overtime.
Limitations of this study
The present study had several limitations. First, its cross-sectional nature limits causal inferences that can be derived from the findings. Second, because of the loose definition of SBS, there have been wide variations among previous studies in terms of the symptoms covered, the time period studied, and the frequency of symptoms and in constructing a summary measure of SBS using these symptoms. The questionnaire administered in the present study was not designed to distinguish between symptoms occurring during workdays and those also occurring on weekends. Thus, we might have counted subjects with symptoms unrelated to the work environment as having SBS. This misclassification would have occurred irrespective of exposure status and would have distorted the estimates toward the null value. Third, employees suffering from SBS symptoms may tend to avoid working overtime, which may have resulted in underestimation of the risks of extensive overtime. Fourth, workplace ETS exposure, overtime work, and symptoms were assessed neither independently nor objectively. Thus, workers who have SBS symptoms might overstate their exposure levels, leading to a stronger association. Such bias is less likely to occur in reports of overtime, which are recorded monthly, and reports of workplace smoking restrictions. Lastly, risk factors for SBS symptoms that were not assessed in the survey, such as use of photocopiers or carbonless copy paper at work (4
, 7
, 25
) or ETS exposure in the home, may have confounded the present association somewhat.
In conclusion, the present findings from a cross-sectional study of Japanese office workers, together with previous findings, support the hypothesis that ETS exposure is a determinant of SBS symptoms in workplaces with a high prevalence of smoking but limited restrictions on smoking, and that extensive overtime work increases the risk of SBS symptoms by affecting working conditions and lifestyle. The intensity of workplace ETS exposure and overtime work in Japan are subject to change. Increasing public concern about the adverse health effects of ETS and changes in government policy on workplace smoking restrictions might lead to a reduction of ETS levels in Japanese offices, while corporate downsizing would increase the workload for each employee. The present findings should be confirmed by future studies examining whether changes in exposure levels of such factors reduce or increase the prevalence of SBS symptoms.
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ACKNOWLEDGMENTS
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This study was supported by a Grant-in-Aid for Encouragement of Young Scientists from the Japanese Ministry of Education, Science, Sports, and Culture.
The authors thank the staff of the safety and health section of the Kitakyushu city office and Yoko Wada for their help in conducting the survey.
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NOTES
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Reprint requests to Dr. Tetsuya Mizoue, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan (e-mail: mizoue{at}med.uoeh-u.ac.jp).
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Received for publication August 8, 2000.
Accepted for publication May 25, 2001.