Abstract
BackgroundThe impact of long working hours on diabetes is controversial; however, shift work is known to increase the risk of diabetes. This study aimed to investigate the association between long working hours and diabetes among civil servants in Japan separately by shift work schedules.MethodsA prospective cohort study was conducted from April 2003 to March 2009. A total of 3195 men aged ≥35 years who underwent an annual health checkup at baseline were analyzed by shift work schedules (2371 non-shift workers and 824 shift workers). Self-reported working hours were categorized as 35–44 and ≥45 hours per week. The incidence of diabetes was confirmed by fasting plasma glucose concentration ≥126 mg/dL and/or self-reported medical diagnosis of diabetes at the annual checkup. A Cox proportional model was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for developing diabetes associated with long working hours.ResultsThe median follow-up period of non-shift and shift workers was 5.0 and 4.9 years, respectively. During this period, 138 non-shift workers and 46 shift workers developed diabetes. A decreased HR was found among non-shift workers working ≥45 hours per week (HR 0.84; 95% CI, 0.57–1.24); however, shift workers working ≥45 hours per week had a significantly increased risk of diabetes (HR 2.43; 95% CI, 1.21–5.10) compared with those working 35–44 hours per week. An analysis restricted to non-clerical workers also showed similar results.ConclusionsThe risk of diabetes associated with long working hours differed by shift work schedules.
Highlights
Long working hours is an important public health concern because of possible harmful effects on human health
The average annual hours worked per worker in Organisation for Economic Co-operation and Development (OECD) countries decreased gradually from 1843 hours in 2000 to 1770 hours in 2013; a similar trend was observed in Japan, where annual hours per worker decreased from 1821 hours in 2000 to 1734 hours in 2013.2 it was estimated that 22.0% of workers worldwide worked more than 48 hours per week in 2007.3 In Japan, the proportion of workers working ≥49 hours per week was 22.9% in 2009 and 21.7% in 2013.4 that proportion among civil servants in Japan increased from 17.4% in 2000 to 34.2% in 2010.5 it should be recognized that certain workers continue to work long hours
Referring to a previous report,[11] possible reasons for this inconsistency might include differences in the study design, participant characteristics, categorization of working hours, the definition of diabetes, and the approach to shift work schedules. We focused on the latter factor, because a previous review argued that it is important to deal properly with shift work schedules for clear interpretation,[1] and a recent meta-analysis concluded that shift work is associated with an increased risk of diabetes.[12]
Summary
Long working hours is an important public health concern because of possible harmful effects on human health. Several studies have investigated the association between long working hours and diabetes[7,8,9,10]; the results were limited and inconsistent. From the results of three cohort studies,[7,8,9] Kawakami et al indicated that long working hours significantly increased the risk of diabetes among Japanese male industrial workers.[7] In contrast, one other study found a significantly decreased risk of diabetes in male office workers working long hours in Japan.[8] no association was. The impact of long working hours on diabetes is controversial; shift work is known to increase the risk of diabetes. This study aimed to investigate the association between long working hours and diabetes among civil servants in Japan separately by shift work schedules. Conclusions: The risk of diabetes associated with long working hours differed by shift work schedules
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