Abstract
Aim
Understanding work-related factors associated with regular exercise in employees could be useful for determining appropriate interventions to prevent the onset and aggravation of diabetes. This study aimed to assess the associations among work-related stress and mental fatigue, and regular exercise in Japanese employees with or without diabetes.
Methods
This cross-sectional study was conducted in 2018, and included 2916 full-time employees aged older than 40 years without cardiovascular disease, cancer, respiratory disease, kidney disease, disc herniation, and depression. Work-related stress was measured by the Job Content Questionnaire and work-related mental fatigue was measured using the Numerical Rating Scale (NRS).
Results
Regular exercise was present in 23.9% of 117 employees with diabetes and in 21.3% of 2799 employees without diabetes. In employees with diabetes, the multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for regular exercise were 0.26 (0.07–0.96) in those with an NRS score of 4–6 (moderate) and 0.22 (0.06–0.85) in those with an NRS score of 7–10 (severe) compared with those with an NRS score of 0–3 (none or mild), after adjusting for confounding factors. Similarly, in employees without diabetes, the multivariable-adjusted ORs (95% CIs) for regular exercise were 0.77 (0.62–0.97) in those with an NRS score of 4–6 and 0.75 (0.59–0.94) in those with an NRS score of 7–10 compared with those with an NRS score of 0–3.
Conclusions
Work-related mental fatigue was negatively associated with regular exercise in employees with and without diabetes.
Electronic supplementary material
The online version of this article (10.1007/s13340-019-00410-z) contains supplementary material, which is available to authorized users.
Keywords: Work-related stress, Work-related mental fatigue, Regular exercise, Diabetes
Introduction
A recent study reported that there were 425 million adults with diabetes worldwide in 2017, and more than two-thirds of those were of working age (327 million) [1, 2]. Diabetes not only leads to a huge health burden, but also imposes a large economic burden [3]. A recent study, which estimated the diabetes-related economic cost among adults of working age in Asia, showed that the cost of productivity loss was substantial [4]. Therefore, preventing the onset and aggravation of diabetes among employees is important not only for employees, but also for companies and society from the viewpoint of productivity and economic burden.
Regular exercise prevents the onset of diabetes [5], and it contributes to weight loss and improves blood glucose control in people with diabetes [6, 7]. Therefore, regular exercise is an important factor for preventing the onset and aggravation of diabetes. However, the majority of Japanese adults of working age do not exercise regularly, even those with diabetes [8, 9]. Understanding the factors associated with regular exercise in employees could be useful for determining appropriate interventions to support regular exercise.
Recently, the importance of preventing the onset of diabetes among adults of working age and supporting for coexisting diabetes treatment and work (Ryoritsu Shien) has been highlighted [10, 11]. Thus, research focusing on work-related factors that are closely linked to employees’ lives is needed. However, although previous studies have shown that personal factors, such as education level, sense of coherence (SOC), and living alone, are associated with regular exercise [12–14], few studies have evaluated the effects of work-related factors on regular exercise [13, 15]. In these previous studies, work-related factors, such as physical labor, late-night work, and long working hour, were negatively associated with regular exercise [13, 15]. However, easily modifying those work-related factors may not be possible. Work-related stress and mental fatigue are currently major concerns [16]. However, little is known about the associations among work-related stress and mental fatigue, and regular exercise in employees with or without diabetes. Therefore, we assessed the associations among work-related stress and mental fatigue, and regular exercise in Japanese employees with or without diabetes.
Methods
Study participants
This study was designed to clarify work-related factors that are important for preventing the onset of diabetes among people of working age and supporting for coexisting diabetes treatment and work (Ryoritsu Shien). This survey was conducted in 2018, and included 7778 general, full-time employees aged older than 20 years, working at a company with approximately 150 branches and offices across 27 prefectures in Japan. The process of selecting study participants is shown in Supplementary Figure S1. Of 7778 employees, 6689 (86.0%) employees agreed to participate in the questionnaire survey. Additionally, we included 3858 employees aged older than 40 years because specific health checkups focusing on visceral fat obesity for insured people aged 40 years or older are required in Japan. Of 3339 employees who agreed to have specific health checkup data used, we excluded those with cardiovascular disease, such as coronary heart disease, cardiac heart disease, arrhythmia, and cerebrovascular disease, those with cancer, those with respiratory disease, such as chronic obstructive pulmonary disease and asthma, those with kidney disease, those with disc herniation, those with depression, and those with missing data. A total of 2916 employees were included in the analysis.
The study protocol was written in accordance with the Declaration of Helsinki and was approved by the Institutional Review Boards of Osaka University (date of approval 24 December 2017; approval no. 17233) and Osaka Prefecture University (date of approval 2 March 2018; approval no. 29-62). Informed consent was obtained from all participants who were included in the study.
Definition of diabetes
Among the results of the specific health checkups, the medical history was used in the study. The presence of diabetes was defined by a history of diabetes (i.e., having received treatment for diabetes or having taken antidiabetic medication).
Main exposures: work-related stress and mental fatigue
Information on work-related stress and mental fatigue was obtained using a self-administered questionnaire. Work-related stress was measured by the Japanese version of the Job Content Questionnaire (JCQ). The reliability and validity of the JCQ are considered excellent for assessing work-related stress among Japanese employees [17, 18]. Psychological job demand was measured with five items regarding the speed in completing work, the degree of difficulty of the work, the amount of work, the time allowed to complete the work, and conflicting job demands. Job control was measured with nine items of skill discretion (six items) and decision authority (three items). Job support was measured with eight items of social support (emotional and instrumental support) from supervisors (four items) and coworkers (four items). Items were scored on a 4-point Likert scale ranging from 1 (strongly disagree) to 4 (strongly agree). The score of job demand ranges from 12 to 48, and higher scores indicate higher job demand. The score of job control ranges from 24 to 96, and higher scores indicate that a person can control his/her work. The score of job support ranges from 8 to 32 and higher scores indicate more job support. The Cronbach alphas of job demand, job control, and job support in this study were 0.67, 0.72, and 0.88, respectively. Work-related mental fatigue was measured using the Numerical Rating Scale (NRS), and participants rated the severity as 0 (none) to 10 (most severe) scales. The NRS is one of the simplest and most frequently used instruments to measure fatigue, and using established severity levels of 0 (none), 1–3 (mild), 4–6 (moderate), and 7–10 (severe) is recommended [19–21].
Outcome: regular exercise
Data on regular exercise were obtained using a self-administered questionnaire. On the basis of the criteria of the Japanese Ministry of Health, Labour and Welfare [8], people with regular exercise were defined as those who have been continuing daily exercise of 30 min or longer at least 2 days a week for at least a year.
Covariates
The potential covariates obtained using a self-administered questionnaire or specific health checkup data included the following: sex, age, education level, SOC, living alone (yes or no), housework, childcare and care hours per day, BMI, blood pressure, HbA1c, duration of diabetes, frequency of outpatient visits (at least once a month, once in 2 months, or ≤ once in 3 months), knee joint and/or hip joint pain (presence or absence), job type (physical labor or non-physical labor), lifting heavy objects at work (presence or absence), scheduled late-night work (night shift) (presence or absence), and working hours including overtime per week. BMI was calculated as weight (kg) divided by height squared (m2). HbA1c (%) was estimated as a National Glycohemoglobin Standardization Program equivalent value (%) and calculated using the formula HbA1c (%) = 1.02 × HbA1c (Japan Diabetes Society, %) + 0.25% [22]. Education level was categorized as ≤ 12 years or > 12 years. Six years of elementary school education and 3 years of junior high school education are compulsory in Japan. High school education in Japan is for 3 years, and university education in Japan is for 4 years (with 2 or 3 years in the case of a junior college education). SOC is a concept developed by Antonovsky and represents a personal ability to manage psychological stressors [23]. In this study, SOC was assessed using a shortened version of Antonovsky’s SOC questionnaire called the University of Tokyo Health Sociology version of the SOC scale (SOC-UTHS) [24]. The reliability and validity of this scale have been previously confirmed [24]. Items were scored on a 7-point Likert scale ranging from 1 (strongly disagree) to 7 (strongly agree), with higher scores indicating stronger SOC.
Statistical analysis
Participants were stratified by the presence or absence of diabetes. Logistic regression models were used to estimate the sex- and age-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) of each characteristic for regular exercise (response variable: 1 = presence of regular exercise and 0 = absence of regular exercise).
Each of the JCQ scales (job demand scale, job control scale, and job support scale) was classified as a high score group and a low score group by the median (job demand: 31 scores, job control: 62 scores, job support: 22 scores). Because the sample size of those with an NRS score of 0 (none) was small, work-related mental fatigue as measured using the NRS was classified into three severity levels as follows: 0–3 (none or mild), 4–6 (moderate), and 7–10 (severe). The proportions of employees who had regular exercise according to work-related stress and mental fatigue were compared using the χ2 test. Additionally, to identify the associations among work-related stress and mental fatigue, and regular exercise in Japanese employees with or without diabetes, multivariable-adjusted ORs and 95% CIs of each factor for regular exercise were calculated using logistic regression models (response variable: 1 = presence of regular exercise and 0 = absence of regular exercise). Sex, age, education level (≤ 12 years or > 12 years), SOC score, living alone (yes or no), BMI, HbA1c, frequency of outpatient visits (at least once a month, once in 2 months, or ≤ once in 3 months), job type (physical labor or non-physical labor), lifting heavy objects at work (presence or absence), scheduled late-night work (presence or absence), and working hours including overtime were included in the model for employees with diabetes. Sex, age, education level (≤ 12 years or > 12 years), SOC score, living alone (yes or no), BMI, job type (physical labor or non-physical labor), lifting heavy objects at work (presence or absence), scheduled late-night work (presence or absence), and working hours including overtime were included in the model for employees without diabetes.
The proportions of employees who had work-related moderate or severe mental fatigue (NRS score ≥ 4) according to quartile of job support score were compared using the χ2 test. Additionally, logistic regression models (response variable: 1 = NRS score ≥ 4 and 0 = NRS score of 0–3) were used to confirm the association between job support in the JCQ and work-related moderate or severe mental fatigue in Japanese employees with or without diabetes. Sex, age, SOC score, living alone (yes or no), job type (physical labor or non-physical labor), lifting heavy objects at work (presence or absence), scheduled late-night work (presence or absence), and working hours including overtime were included in the model.
All data were analyzed using SPSS statistical software (version 25; IBM SPSS Japan, Tokyo, Japan). All reported p values are two tailed and values < 0.05 were considered statistically significant.
Results
Associations between characteristics and regular exercise in Japanese employees with or without diabetes
Of 2916 employees older than 40 years, 117 employees had diabetes and 2799 employees did not have diabetes. Regular exercise was present in 23.9% of the 117 employees with diabetes and in 21.3% of 2799 employees without diabetes. The characteristics of Japanese employees with or without diabetes are shown in Table 1. The ORs and 95% CIs for regular exercise according to each characteristic are shown in Table 2. In employees with diabetes, the only characteristic that was significantly associated with regular exercise was SOC (OR = 1.15, 95% CI = 1.02–1.30, per 1 score). Similarly, in employees without diabetes, the only characteristic that was significantly associated with regular exercise was SOC (OR = 1.07, 95% CI = 1.05–1.10, per 1 score).
Table 1.
Characteristics, work-related stress, and work-related mental fatigue of Japanese employees with or without diabetes
| Factors | Employees with diabetes | Employees without diabetes |
|---|---|---|
| n | 117 | 2799 |
| Men, (%) | 96.6 | 93.0 |
| Age (years) | 50.4 ± 5.6 | 47.5 ± 5.4 |
| Education level: ≤ 12 years, (%) | 75.2 | 75.2 |
| Sense of coherence (score) | 12.4 ± 4.0 | 12.6 ± 3.8 |
| Living alone, (%) | 17.1 | 14.1 |
| Housework, childcare and care hours: ≥ 1 h/day, (%) | 38.5 | 44.8 |
| Body mass index (kg/m2) | 27.9 ± 4.5 | 23.8 ± 3.7 |
| Systolic blood pressure (mmHg) | 137.2 ± 15.9 | 127.0 ± 15.9 |
| HbA1c (%) | 7.6 ± 1.6 | – |
| Duration of diabetes (years) | 8.3 ± 7.4 | – |
| Frequency of outpatient visits, (%) | ||
| At least once a month | 55.6 | – |
| Once in 2 months | 30.8 | – |
| ≤ Once in 3 months | 13.7 | – |
| Knee joint and/or hip joint pain: presence, (%) | 51.3 | 46.9 |
| Job type: physical labor, (%) | 61.5 | 64.6 |
| Lifting heavy objects at work: presence, (%) | 23.9 | 30.9 |
| Scheduled late-night work: presence, (%) | 47.9 | 48.3 |
| Working hours including overtime (h/week) | 45.6 ± 6.1 | 48.3 ± 6.7 |
| Work-related stress | ||
| Job demand (score) | 30.5 ± 4.8 | 31.5 ± 5.9 |
| Job control (score) | 61.8 ± 10.8 | 60.7 ± 11.2 |
| Job support (score) | 21.7 ± 4.0 | 21.6 ± 4.3 |
| Work-related mental fatigue, (%) | ||
| NRS, 0–3 (none or mild) | 32.5 | 30.4 |
| NRS, 4–6 (moderate) | 34.2 | 36.5 |
| NRS, 7–10 (severe) | 33.3 | 33.1 |
Continuous data are shown as mean ± standard deviation
NRS Numerical Rating Scale
Table 2.
Odds ratios and 95% confidence intervals for regular exercise according to each characteristic in Japanese employees with or without diabetes
| Factors | Comparison | Employees with diabetes | Employees without diabetes |
|---|---|---|---|
| Sex- and age-adjusted OR (95% CI) for regular exercise | Sex- and age-adjusted OR (95% CI) for regular exercise | ||
| Education level: ≤ 12 years | Vs. > 12 years | 0.60 (0.22–1.66) | 0.82 (0.67–1.01) |
| Sense of coherence | Per 1 score | 1.15 (1.02–1.30) | 1.07 (1.05–1.10) |
| Living alone | Vs. living together | 0.27 (0.06–1.27) | 0.94 (0.73–1.23) |
| Housework, childcare and care hours (/day) | Per 1 h | 1.04 (0.78–1.39) | 0.99 (0.93–1.05) |
| Body mass index: ≥ 25.0 kg/m2 | Vs. < 25.0 kg/m2 | 1.84 (0.65–5.18) | 0.98 (0.81–1.20) |
| Systolic blood pressure | Per 10 mmHg | 0.90 (0.68–1.20) | 1.03 (0.97–1.09) |
| HbA1c: ≥ 7.0% | Vs. < 7.0% | 2.39 (0.90–6.31) | – |
| Duration of diabetes | Per 1 year | 0.99 (0.93–1.06) | – |
| Frequency of outpatient visits | |||
| Once in 2 months | Vs. at least once a month | 0.97 (0.37–2.56) | – |
| ≤ Once in 3 months | Vs. at least once a month | 0.81 (0.19–3.37) | – |
| Knee joint and/or hip joint pain: presence | Vs. absence | 1.03 (0.43–2.47) | 1.04 (0.86–1.24) |
| Job type: physical labor | Vs. non-physical labor | 0.60 (0.25–1.47) | 1.02 (0.84–1.24) |
| Lifting heavy objects at work: presence | Vs. absence | 0.88 (0.31–2.52) | 0.89 (0.78–1.03) |
| Scheduled late-night work: presence | Vs. absence | 0.66 (0.27–1.61) | 0.87 (0.72–1.04) |
| Working hours including overtime (/week) | Per 5 h | 0.55 (0.34–1.02) | 1.03 (0.96–1.10) |
Response variable: 1=presence of regular exercise, 0=absence of regular exercise
Sense of coherence is a concept that represents a personal ability to manage psychological stressors, with higher scores indicating a stronger sense of coherence
OR odds ratio, CI confidence interval
Associations among work-related stress and mental fatigue, and regular exercise in Japanese employees with or without diabetes
Work-related stress and mental fatigue of Japanese employees with or without diabetes are shown in Table 1. The proportions of employees who had regular exercise according to work-related stress and mental fatigue are shown in Table 3. In employees with diabetes, the proportions of employees who had regular exercise according to job support in the JCQ were 35.7% in the high score group and 17.3% in the low score group (p = 0.025). The proportions of employees who had regular exercise according to work-related mental fatigue were 36.8% in those with an NRS score of 0–3, 22.5% in those with an NRS score of 4–6, and 12.8% in those with an NRS score of 7–10 (p = 0.046). In employees without diabetes, the proportions of employees who had regular exercise according to job support in the JCQ were 24.1% in the high score group and 19.3% in the low score group (p = 0.002). The proportions of employees who had regular exercise according to work-related mental fatigue were 24.2% in those with an NRS score of 0–3, 19.9% in those with an NRS score of 4–6, and 20.2% in those with an NRS score of 7–10 (p = 0.047).
Table 3.
Proportions of employees who had regular exercise according to work-related stress and mental fatigue in Japanese employees with or without diabetes
| Factors | Comparison | Employees with diabetes | Employees without diabetes | ||
|---|---|---|---|---|---|
| Proportion of employees who had regular exercise % (case/n) |
p value | Proportion of employees who had regular exercise % (case/n) |
p value | ||
| Work-related stress | |||||
| Job demanda | Low score group | 23.5 (16/68) | 0.904 | 21.7 (319/1473) | 0.621 |
| High score group | 24.5 (12/49) | 20.9 (277/1326) | |||
| Job controla | High score group | 25.4 (16/63) | 0.688 | 22.3 (321/1438) | 0.172 |
| Low score group | 22.2 (12/54) | 20.2 (275/1361) | |||
| Job supporta | High score group | 35.7 (15/42) | 0.025 | 24.1 (283/1176) | 0.002 |
| Low score group | 17.3 (13/75) | 19.3 (313/1623) | |||
| Work-related mental fatigue | NRS, 0–3 (none or mild) | 36.8 (14/38) | 0.046 | 24.2 (206/852) | 0.047 |
| NRS, 4–6 (moderate) | 22.5 (9/40) | 19.9 (203/1021) | |||
| NRS, 7–10 (severe) | 12.8 (5/39) | 20.2 (187/926) | |||
Higher scores of the job demand scale indicate higher job demand. Higher scores of the job control scale indicate that the employee can control his work. Higher scores of the job support scale indicate more job support
NRS Numerical Rating Scale
aEach of the JCQ scales was classified as a high score group and a low score group by the median
The multivariable-adjusted ORs and 95% CIs for regular exercise according to work-related stress and mental fatigue are shown in Table 4. In employees with diabetes, work-related mental fatigue was negatively associated with regular exercise. After adjusting for sex, age, education level, SOC score, living alone, BMI, HbA1c, frequency of outpatient visits, job type, lifting heavy objects at work, scheduled late-night work, and working hours including overtime, the multivariable-adjusted ORs (95% CIs) for regular exercise were 0.26 (0.07–0.96) in those with an NRS score of 4–6 and 0.22 (0.06–0.85) in those with an NRS score of 7–10 compared with those with an NRS score of 0–3. In employees without diabetes, low job support and work-related mental fatigue were negatively associated with regular exercise. After adjusting for sex, age, education level, SOC score, living alone, BMI, job type, lifting heavy objects at work, scheduled late-night work, and working hours including overtime, the multivariable-adjusted OR (95% CI) for regular exercise was 0.78 (0.65–0.94) in the low score group of job support compared with the high score group of job support. Similarly, the multivariable-adjusted ORs (95% CIs) for regular exercise were 0.77 (0.62–0.97) in those with an NRS score of 4–6 and 0.75 (0.59–0.94) in those with an NRS score of 7–10 compared with those with an NRS score of 0–3.
Table 4.
Multivariable-adjusted odds ratios and 95% confidence intervals for regular exercise according to work-related stress and mental fatigue in Japanese employees with or without diabetes
| Factors | Comparison | Employees with diabetes | Employees without diabetes | ||
|---|---|---|---|---|---|
| Sex- and age-adjusted OR (95% CI) for regular exercise | Multivariable-adjusted OR (95% CI) for regular exercise† | Sex- and age-adjusted OR (95% CI) for regular exercise | Multivariable-adjusted OR (95% CI) for regular exercise‡ | ||
| Work-related stress | |||||
| Job demand: high score groupa | Vs. low score group | 1.20 (0.49–2.91) | 1.52 (0.49–4.71) | 0.94 (0.79–1.13) | 0.89 (0.74–1.08) |
| Job control: low score groupa | Vs. high score group | 0.82 (0.34–1.99) | 1.22 (0.43–3.47) | 0.88 (0.73–1.05) | 0.96 (0.79–1.16) |
| Job support: low score groupa | Vs. high score group | 0.40 (0.17–0.99) | 0.41 (0.14–1.19) | 0.76 (0.63–0.91) | 0.78 (0.65–0.94) |
| Work-related mental fatigue | |||||
| NRS, 4–6 (moderate) | Vs. NRS, 0–3 (none or mild) | 0.48 (0.17–1.14) | 0.26 (0.07–0.96) | 0.78 (0.63–0.97) | 0.77 (0.62–0.97) |
| NRS, 7–10 (severe) | Vs. NRS, 0–3 (none or mild) | 0.26 (0.08–0.84) | 0.22 (0.06–0.85) | 0.79 (0.63–0.99) | 0.75 (0.59–0.94) |
Response variable: 1 = presence of regular exercise, 0 = absence of regular exercise
OR odds ratio, CI confidence interval, NRS Numerical Rating Scale
†Adjusted for sex, age, education level, sense of coherence score, living alone, body mass index, HbA1c, frequency of outpatient visits, job type, lifting heavy objects at work, scheduled late-night work, and working hours including overtime
‡Adjusted for sex, age, education level, sense of coherence score, living alone, body mass index, job type, lifting heavy objects at work, scheduled late-night work, and working hours including overtime
aEach of the JCQ scales was classified as a high score group and a low score group by the median
Association between job support in the JCQ and work-related mental fatigue in Japanese employees with or without diabetes
The proportions of employees who had work-related moderate or severe mental fatigue (NRS score ≥ 4) according to quartile of job support score in Japanese employees with or without diabetes are shown in Fig. 1. In employees with diabetes, the proportions of employees who had work-related moderate or severe mental fatigue (NRS score ≥ 4) according to the quartile of job support score were 92.3% in those with scores ≤ 19 (the lowest quartile, quartile 1), 63.0% in those with scores of 20–23 (quartile 2), 61.2% in those with scores of 24–25 (quartile 3), and 53.3% in those with scores ≥ 26 (the highest quartile, quartile 4) (p = 0.020). In employees without diabetes, the proportions of employees who had work-related moderate or severe mental fatigue (NRS score ≥ 4) according to the quartile of job support score were 82.9% in those with scores ≤ 19 scores (the lowest quartile, quartile 1), 69.5% in those with scores of 20–23 (quartile 2), 62.8% in those with scores of 24–25 (quartile 3), and 60.7% in those with scores of ≥ 26 (the highest quartile, quartile 4) (p < 0.001). Additionally, after adjusting for sex, age, SOC score, living alone, job type, lifting heavy objects at work, scheduled late-night work, and working hours including overtime, employees in the lowest quartile (quartile 1) of job support score had significantly elevated risks of work-related moderate or severe mental fatigue (NRS score ≥ 4) in those with diabetes (the multivariable-adjusted OR for lowest Vs. highest quartiles, 21.25 [95% CI, 1.97–229.18]; p for trend = 0.015) and those without diabetes (the multivariable-adjusted OR for lowest Vs. highest quartiles, 3.16 [95% CI, 2.34–4.27]; p for trend < 0.001).
Fig. 1.
Proportions of employees who had work-related moderate or severe mental fatigue (NRS score ≥ 4) according to quartile of job support score in Japanese employees with or without diabetes. NRS Numerical Rating Scale, Q quartile
Discussion
The main finding of the present study was that work-related mental fatigue was negatively associated with regular exercise in employees with diabetes, after adjusting for confounding factors. To lose weight and improve blood glucose control, those with diabetes need to exercise regularly. In this study, although the mean BMI and HbA1c levels of employees with diabetes were 27.9 kg/m2 and 7.6%, respectively, the proportion of those who had regular exercise was only 23.9%. This proportion is similar to that found in the general population in a recent report in Japan [8]. Therefore, nurses, physicians, and physical therapists should promote and support regular exercise in employees with diabetes. In this study, the proportion of employees with diabetes who had regular exercise was relatively low in those with work-related moderate or severe mental fatigue. Mental fatigue is a state caused by prolonged periods of demanding cognitive activity and is characterized by subjective feelings of tiredness and lack of energy [25]. An experimental study conducted on healthy adults reported that mental fatigue limits exercise tolerance because of perceiving considerable effort during exercise [26]. Employees with diabetes who have work-related moderate or severe mental fatigue may perceive considerable effort in exercise therapy and may not be able to start or continue exercise. The NRS is one of the simplest instruments for measuring fatigue, enabling nurses, physicians, and physical therapists to easily assess the severity of work-related mental fatigue during outpatient visits. To promote and support regular exercise among employees with diabetes, we believe that nurses, physicians, and physical therapists need to assess employees’ work-related mental fatigue. Additionally, although there was no significant association between job support and regular exercise in employees with diabetes in this study, the proportion of those with diabetes who had work-related moderate or severe mental fatigue was relatively high among those in the lowest quartile of job support score. Moreover, those with diabetes in the lowest quartile of job support score had an elevated risk of work-related moderate or severe mental fatigue, after adjusting for confounding factors. Therefore, our findings suggest that low job support may be indirectly associated with regular exercise by contributing to an increase in work-related mental fatigue among those with diabetes. Recently, the importance of supporting for coexisting diabetes treatment and work (Ryoritsu Shien) has been highlighted [10, 11], and cooperation between hospitals and workplaces using support notebooks for coexisting diabetes treatment and work has been promoted [10]. Importantly, approximately 60% of all workers in Japan are employed in workplaces with less than 50 workers, which are not obliged to appoint an occupational physician [27]. Therefore, to prevent a low level of job support in the workplace and work-related moderate or severe mental fatigue among employees with diabetes, we believe that nurses, physicians, and physical therapists need to actively cooperate with workplaces.
Work-related mental fatigue and low job support were also negatively associated with regular exercise in employees without diabetes, after adjusting for confounding factors. Therefore, the present findings support the conclusion that work-related mental fatigue and low job support are important work-related factors that can interfere with regular exercise in employees with or without diabetes. A recent study reported that frequent conflicts with supervisors or coworkers were associated with mental fatigue [28]. Preventing onset and aggravation of diabetes is important not only for employees, but also for companies from the viewpoint of productivity and economic burden. Therefore, we believe that not only occupational health practitioners but also managers in companies need to recognize the importance of supportive attitudes from employee’s supervisors and coworkers.
The strengths of the present study are as follows: (1) a relatively large sample of employees, which consisted of those from many prefectures throughout Japan, (2) a high response rate, and (3) large-scale data that included extensive data on potential confounding factors. However, this study also has several limitations. First, a cross-sectional design cannot prove causality. Therefore, a prospective study is necessary. Second, we cannot deny the possibility of selection bias because the participants were limited to employees of one company. However, the company has approximately 150 branches and offices across 27 prefectures in Japan, and we included all general, full-time employees of the company. In addition, we compared the proportions of individuals who were strongly suspected of having diabetes in this study and in the National Health and Nutrition Survey 2016 in Japan [29] (Supplementary Table S1). Because the definition of diabetes was different between this study and the National Health and Nutrition Survey, we calculated the proportion of individuals who were strongly suspected of having diabetes among 3339 employees aged older than 40 years who agreed to have specific health checkup data used. As a result of comparison, there were no significant differences in the proportions of individuals who were strongly suspected of having diabetes in this study and in the National Health and Nutrition Survey 2016 in Japan (Supplementary Table S1). Additionally, the proportion of employees who had regular exercise in this study is similar to that found in the National Health and Nutrition Survey in Japan [8]. Third, other potential confounding factors that were not considered in this study included exercise habits, when participants were young, and the level of physical labor. Finally, we did not investigate the type of regular exercise (e.g., walking, jogging, or swimming).
Despite these potential limitations, the present findings support the conclusion that work-related mental fatigue and low job support are important work-related factors that can interfere with regular exercise in employees with or without diabetes. We believe that nurses, physicians, and physical therapists need to focus their attention on work-related mental fatigue and job support to promote and support regular exercise in employees with or without diabetes.
Electronic supplementary material
Below is the link to the electronic supplementary material.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (Grant number: 18H03118). We gratefully acknowledge all the employees who participated in this study.
Author contributions
AM designed the study, acquired the data, performed the analyses, and wrote the manuscript. SW and YO designed the study, acquired the data, performed data interpretation, and contributed to editing of the manuscript. KG acquired the data, performed data interpretation, and contributed to editing of the manuscript. CH, YS, SO, and MS performed data interpretation and contributed to editing of the manuscript. NS designed the study, acquired the data, performed data interpretation, and contributed to editing of the manuscript. All authors approved the final version of the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Human rights statement
All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1964 and later versions.
Informed consent
Informed consent or substitute for it was obtained from all patients for being included in the study.
Footnotes
Publisher's Note
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