Health problems associated with single, multiple, and the frequency of months of objectively measured long working hours: a cohort study by the National Institute of Occupational Safety and Health, Japan

Abstract

Purpose We aimed to examine the prospective associations of monthly working hours measured in a month, the 6-month averaged hours, and the frequency of long working hours (≥ 205 h/month) during the past 6 months with health indicators. Methods This study included 6,806 Japanese company workers (response rate = 86.6%). Data on the workers’ monthly attendance during the second half of fiscal year 2016 and annual health checkups in fiscal years 2016 and 2017 were collected. We evaluated the association of the above three types of monthly working hours with subsequent health checkup data in fiscal year 2017. We adjusted for the corresponding data in fiscal year 2016. Results Multivariate logistic regression analyses revealed significant associations between monthly working hours and workers’ systolic and diastolic blood pressure as well as aspartate aminotransferase, alanine aminotransferase, low-density lipoprotein cholesterol (LDL), and triglyceride levels. However, the associations were not consistent between months. The average monthly working hours were significantly associated with higher LDL levels for the 220–240 h/mo group (OR: 1.49, 95%CI: 1.07–2.08) and lower triglyceride levels for the < 140 h/mo group (OR: 0.15, 95%CI: 0.03–0.77), compared to the 140–180 h/mo group. The frequency of long working hours was significantly associated with higher LDL levels. Conclusions Working hours over several months produced various associations with health indicators compared to those measured in a single month. Our present data suggest that the effects of average or frequency of long working hours during the past 6 months are likely to appear in LDL levels.

Characteristics of long working hours and subsequent psychological and physical responses: JNIOSH cohort study

“…The slope of the response curve for ‘lack of vigour’ increased gradually at the lowest stress level, followed by a sharp increase in ‘irritability’ and ‘fatigue’ the same number of times, followed by a sharp increase in ‘anxiety’. Moreover, ‘depression’ was rarely reported at low stress levels, whereas the highest stress level was associated with a sharp increase in ‘depression’ 30. The IRT results indicate that psychological stress responses may manifest in this order with an increase in stress levels.…”

“…Moreover, ‘depression’ was rarely reported at low stress levels, whereas the highest stress level was associated with a sharp increase in ‘depression’. 30 The IRT results indicate that psychological stress responses may manifest in this order with an increase in stress levels. In contrast, physical stress responses do not show a clear threshold, suggesting that physical stress responses may be underscored by factors other than stress.…”

“…5. The workers were divided into six groups according to their AWH, based on previous studies and meta-analyses, 25 26 and to the upper limit of overtime hours in Japan (45 hours overtime per month, equivalent to 205 working hours per month as the prescribed working hours are 160 hours per month), 30 as follows: <140 hours/month (equivalent to >35 hours/week), 140–180 hours/month (35–45 hours/week), 180–205 hours/month (45–51.25 hours/week), 205–220 hours/month (51.25–55 hours/week) and≥220 hours/month (≥55 hours/week) groups.…”

“…In our ongoing series of studies, we focused on measuring working hours as an exposure factor. Our analysis revealed the need to identify objective approaches to measure working hours that consider a certain period of time rather than a single point in time 29 30. Hence, this exploratory study aimed to examine the association of 6-month average (total) working hours (AWH; objectively measured) and frequency (intensity) or accumulation of long working hours (FLWH) over a 6-month period with workers’ subsequent psychological and physical stress reactions.…”