In this study, we used data collected from questionnaires completed by women and men who were members of the police force in Japan to examine the relationship between stress and lifestyle factors, particularly changes in sleep patterns. These questionnaires were given at annual health check-ups and the completion rate was 100%. In this study cohort, women were more likely to have short sleep duration (< 5 h/day) than men. This decrease in sleep was associated with significantly higher risk for various outcomes for stress and stress responses (Tables 3, 4, 5, 6, 7, 8, and 9). Men and women who reported having less sleep had higher risk for high stress, depressive feeling, and somatic symptoms whereas the risk for irritability in men and fatigue in women was significantly higher. Together, these results indicate that short sleep duration is associated with physical and mental stress reactions in both men and women. For women in particular, short sleep duration had the highest number of associated high-risk items among the 12 factors studied. Among these, the lower limit of the odds ratio was 1.78 for fatigue, indicating a strong association with short sleep duration (Table 6).

In women, short sleep duration may be due to other reasons than job workload such as burdens at home like housework and childcare. Approximately 70% of men and 40% of women in the study group were married and the effects of marital status on stress reactions differed significantly between men and women. Married men had a lower risk of six of the seven stress responses (high stress, vitality, irritability, fatigue, anxiety, and depressive feeling) examined, whereas women had no significant difference in high stress or stress responses based on marital status. Therefore, we examined sleep status based on marital status. The likelihood of short sleep duration also differed among men and women depending on marital status in that unmarried men and married women were more likely to have short sleep duration (Fig. 1).

Shift work may increase the risk of stress reactions in women who are police officers. The police organization under study has a 24-h shift system, and approximately 40% of men and 20% of women engage in shift work. Women who had shift work were at higher risk for irritability, fatigue, and depressive feeling, but no significant risk was seen for men. Except for short sleep duration, shift work showed the significant risk for various stress reactions examined here. Although not statistically significant, women engaged in shift work were 3.2% more likely to have shorter sleep duration than women working daily shifts (Fig. 2).

We next compared risks associated with short sleep duration together with shift work and marital status in terms of gender. Women who were married and engaged in shift work were twice as likely to have short sleep duration than those who were married but worked days (31.9% vs. 15.4%). On the other hand, in men the frequency of short sleep duration was similar between day and shift work (10.1% vs. 10.4%). Together, the fraction of married women who worked shifts and had short sleep duration was three times higher than that for married men who were in shift work (Fig. 3). One explanation for the substantial difference in the association between marital status and stress reactions between men and women is that women spend more time on off-duty days and public holidays attending to domestic roles and have less time to devote to sleep than married men.

At least 30% of married female police officers appeared to have difficulty getting enough sleep, even after a 24-h shift. Short sleep duration increases the risk of fatigue among women, which may have an impact on safety and productivity while on duty. A summary by the Organization for Economic Cooperation and Development (OECD) reported that, on average, Japanese had the fewest number of sleeping hours among 33 countries surveyed, at 7 h and 22 min. Moreover, Japanese women slept 7 h 15 min, 13 min less than men, and Japanese women had the shortest sleep duration in the world (OECD 2021).

“Work–life balance” focuses on preventing overwork, harmonizing work and life, and balancing work and family. In Japan, however, women are responsible for most of the “housework/childcare/caregiving” and thus overwork may be due not only to employment but also the effects of overwork from other activities like housework. As such, in parallel with the changes in family structure in Japan, such as an increase in the number of dual-income households, it is increasingly apparent that men must play a more proactive role in “housework/childcare/caregiving” (Cabinet Office, Government of Japan 2020).

One concept that focuses on the positive aspects of taking on multiple roles in work and family is positive spillover (Bakker and Demerouti 2013). In our study population, 70% of male police officers were married, and married men were at lower risk for most of the stress response items examined. Being married may increase family activeness (e.g., discretion and support at home) that increase “family-to-work positive spillover” (Shimada et al. 2010). Meanwhile, for women, the qualitative and quantitative burden of work might increase such that “work-to-family negative spillover” occurs (Shimada et al. 2010). Therefore, positive spillover as a possible factor to reduce the risk of stress among married male police officers should be considered, while initiatives that can mitigate negative spillover among married female police officers are needed. Such initiatives could in turn improve the overall sleep duration of police officers as a whole. Among men and women police officers who are not married, the burden of household chores is expected to increase, particularly if they are raising children or are in charge of caring for family members. Thus, the roles of single officers in the household may vary in multiple ways. We believe that favorable results obtained from efforts to reduce the frequency of “short sleep duration” and increase good stress status in married men could be expanded more broadly to police officers who have various family compositions.

Rhythm of daily life was another strong factor that influenced multiple stress responses. In this study population, around 20% of both men and women reported having an irregular rhythm of daily life. For men, irregular rhythm of daily life was associated with higher risk for all seven stress categories: high stress, vitality, irritability, fatigue, anxiety, depressive feeling, and somatic symptoms. Among women with irregular rhythm of daily life, the risk was higher for only somatic symptoms. We observed no apparent increased risk for shift work among men, suggesting that maintaining a regular rhythm of daily life may be more beneficial for stress reactions than a decrease in shift work among police officers. Police officers often cannot easily control their working schedules and thus tend to have irregular rhythm of daily life since they are required to respond to accidents, investigate crimes, and perform security duties at various times, regardless of whether they are engaged in shift-work or day-work. Irregular rhythm of daily life can also impact sleep patterns. Both short sleep duration and irregular sleep are shown to be associated with disease onset, progression, and mortality (Kubo et al. 2021; Omichi et al. 2022). Furthermore, irregular work schedules can compromise engagement in the full range of activities of an individual’s personal life and eventually affect self-care such as exercise and rest, as well as interactions with family and friends. Such effects on family lives could also affect interactions with family members, reducing the positive spillover that being married provides. As such, the negative spillover from work to family is likely to be greater.

Shimada et al. reported that contemporary society has more dual-earner families and longer working hours, and thus maintaining a balance between work and family roles is becoming an important issue for both males and females (Shimada et al. 2010). Therefore, from the perspective of management, supporting individuals who are coping with factors outside the workplace that are affecting their family lives is important and may help ensure appropriate sleep duration and rhythm of daily life. Police officers in particular often have difficulty avoiding work on days off due to the conventional organizational atmosphere of the police force that discourages days off. However, police organizations should attempt to manage the work of police officers while taking into account responsibilities they may have at home which will promote work–life balance throughout the workplace and increase work engagement of individual officers. Such increased work engagement should enhance positive emotions of officers that will in turn have a positive impact on family life and reinforce positive spillover from work to home (Bakker and Demerouti 2013; Bakker et al. 2014; Shimazu et al. 2009).

Although police officers may be required to work overtime and on days off, the atmosphere in the workplace has been changing in recent years such that employees who have a variety of circumstances, such as housework, childcare, and nursing care responsibilities, can continue working. However, simply shortening the working hours of employees who cannot work overtime is insufficient to ensure that workers have adequate support. Creation of a favorable work environment that is accepting of obligations outside of work can enhance work engagement of workers who are unable to work overtime or on days off, providing the opportunity to advance their careers as police officers. For those employees who are more likely to be required to work overtime or work on days off, such as single or younger employees, work–life balance can be promoted by understanding and giving consideration to their sleep duration, life rhythm, and awareness of fatigue in the workplace, thereby promoting self-care and enrichment of these individuals’ lives outside of work. The provision of lifestyle considerations will enable diverse staff members to work together to create a crossover effect (Bakker et al. 2014; Shimazu et al. 2009) that can further increase work engagement of workers. Fewer days off was also associated with several outcomes in men and women, suggesting the importance of days off in police officers.

Due to the very specific nature of their job demands, police officers are expected to have a higher level of mental and physical health than the general public. Therefore, officers may tend to refrain from disclosing negative information about their own mental and health conditions to avoid potential damage to their careers (Marshall et al. 2021). Officers may instead be less resistant to answer questions concerning their daily life, such as sleeping hours and rhythm of daily life, compared to answering questions about their mental conditions. Information about factors associated with daily life can be an important indicator to accurately assess physical condition and fatigue. Considering the very specific nature of the police profession, health management teams in police departments could promote health management based on daily life information that officers may more freely provide while strictly protecting the health information of each individual.

In terms of rank, the risk of high stress, anxiety, and somatic symptoms was lower for men who had higher rank. In addition, the risk of irritability was lower for men who had achieved chief inspector or higher. Among women, the risk of somatic symptoms was lower for those who had the rank of chief inspector or higher. This lower risk of stress responses among both men and women officers of higher rank may be due to the lower likelihood of their working in the field, of engaging in shift work, and working overtime, such that they may more easily maintain a regular rhythm of daily life. In addition, the higher ranks were more likely to have better job control, which also reduced the risk of stress responses. Actually in this study, low job control measured by BJSQ was significantly less frequent at higher rank in men. For women, clear results could not be detected since fewer women than men had achieved higher ranks.

For men, smoking decreased the risks for low vitality and high fatigue, whereas for women smoking increased the risk of low vitality. Mental illness has been associated with both higher rates and amounts of smoking in the United States and Australia (Lawrence et al. 2009). Therefore, the results seen here may not be an effect of smoking per se. Since smoking is not usually allowed inside office buildings in Japan, smokers must go outside to a designated area where smoking is allowed. Such smoking areas could provide social opportunities as smokers could engage in conversation with others. However, in our study population, few women (6%) were smokers, suggesting that they would have few same-sex colleagues to chat with while smoking. Moreover, the risks associated with smoking are especially serious for women (Tsuji 2020), and here women may smoke, despite these risks, as a way to reduce stress reactions. As a preventive mental health measure, nonsmokers should also be provided with short breaks during which they can leave the workplace and chat with other employees.

One limitation of this study was that the prevalence of high stress and stress responses was generally low. As noted above, officers may tend to avoid releasing their actual mental status, yielding possibilities of low detection power and type II error. However, we believe that the significant results in this study are sufficiently reliable because of the large sample size. Another limitation was that the present study population had substantially fewer women than men, so future research should focus on stressors that are specific to women, such as conflicts between home and work, as well as holiday and overtime work of police officers. Furthermore, we could not implement a validated questionnaire that could completely quantify lifestyle factors. Since this survey was conducted at the time of the legally required annual health screenings, the questionnaire was intended to obtain a broad picture of lifestyle factors while avoiding excessively burdening participants. As for anonymity, the participants may not have dared to give honest answers to the questions on mental health that required a notation. However, the stress check program requires feedback from occupational health staff to the workers with high stress. Therefore, the results of this survey, which is not anonymous, would be more useful for generalization to other workplaces where names are required.

Due to the cross-sectional design, a strict causal relationship may not be proven in the present study. As a healthy worker effect, people with higher stress and susceptible to such stress may have already left the workforce. In addition, the questions for the lifestyle factors was broad, which would lead to a vague measurement of exposure. Future studies should investigate lifestyle habits in detail and longitudinally to clarify the causal relationship of the associations shown in the present study.