The effect of exposure to long working hours on depression: A systematic review and meta-analysis from the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury

Abstract

Background: The World Health Organization (WHO) and the International Labour Organization (ILO) are developing the WHO/ILO Joint Estimates of the Work-related Burden of Disease and Injury (WHO/ILO Joint Estimates), supported by a large number of individual experts. Evidence from previous reviews suggests that exposure to long working hours may cause depression. In this article, we present a systematic review and meta-analysis of parameters for estimating (if feasible) the number of deaths and disability-adjusted life years from depression that are attributable to exposure to long working hours, for the development of the WHO/ILO Joint Estimates.

Objectives: We aimed to systematically review and meta-analyse estimates of the effect of exposure to long working hours (three categories: 41–48, 49–54 and ≥55 h/week), compared with exposure to standard working hours (35–40 h/week), on depression (three outcomes: prevalence, incidence and mortality).

Data sources: We developed and published a protocol, applying the Navigation Guide as an organizing systematic review framework where feasible. We searched electronic academic databases for potentially relevant records from published and unpublished studies, including the WHO International Clinical Trial Registers Platform, Medline, PubMed, EMBASE, Web of Science, CISDOC and PsycInfo. We also searched grey literature databases, Internet search engines and organizational websites; hand-searched reference lists of previous systematic reviews; and consulted additional experts.

Study eligibility and criteria: We included working-age (≥15 years) workers in the formal and informal economy in any WHO and/or ILO Member State but excluded children (aged <15 years) and unpaid domestic workers. We included randomized controlled trials, cohort studies, case-control studies and other non-randomized intervention studies with an estimate of the effect of exposure to long working hours (41–48, 49–54 and ≥55 h/week), compared with exposure to standard working hours (35–40 h/week), on depression (prevalence, incidence and/or mortality).

Study appraisal and synthesis methods: At least two review authors independently screened titles and abstracts against the eligibility criteria at a first stage and full texts of potentially eligible records at a second stage, followed by extraction of data from qualifying studies. Missing data were requested from principal study authors. We combined odds ratios using random-effects meta-analysis. Two or more review authors assessed the risk of bias, quality of evidence and strength of evidence, using Navigation Guide and GRADE tools and approaches adapted to this project.

Results: Twenty-two studies (all cohort studies) met the inclusion criteria, comprising a total of 109,906 participants (51,324 females) in 32 countries (as one study included multiple countries) in three WHO regions (Americas, Europe and Western Pacific). The exposure was measured using self-reports in all studies, and the outcome was assessed with a clinical diagnostic interview (four studies), interview questions about diagnosis and treatment of depression (three studies) or a validated self-administered rating scale (15 studies). The outcome was defined as incident depression in all 22 studies, with first time incident depression in 21 studies and recurrence of depression in one study. We did not identify any study on prevalence of depression or on mortality from depression. For the body of evidence for the outcome incident depression, we had serious concerns for risk of bias due to selection because of incomplete outcome data (most studies assessed depression only twice, at baseline and at a later follow-up measurement, and likely have missed cases of depression that occurred after baseline but were in remission at the time of the follow-up measurement) and due to missing information on life-time prevalence of depression before baseline measurement.

Compared with working 35–40 h/week, we are uncertain about the effect on acquiring (or incidence of) depression of working 41–48 h/week (pooled odds ratio (OR) 1.05, 95% confidence interval (CI) 0.86 to 1.29, 8 studies, 49,392 participants, I2 46%, low quality of evidence); 49–54 h/week (OR 1.06, 95% CI 0.93 to 1.21, 8 studies, 49,392 participants, I2 40%, low quality of evidence); and ≥ 55 h/week (OR 1.08, 95% CI 0.94 to 1.24, 17 studies, 91,142 participants, I2 46%, low quality of evidence).

Subgroup analyses found no evidence for statistically significant (P < 0.05) differences by WHO region, sex, age group and socioeconomic status. Sensitivity analyses found no statistically significant differences by outcome measurement (clinical diagnostic interview [gold standard] versus other measures) and risk of bias ("high"/"probably high" ratings in any domain versus "low"/"probably low" in all domains).

Conclusions: We judged the existing bodies of evidence from human data as "inadequate evidence for harmfulness" for all three exposure categories, 41–48, 48–54 and ≥55 h/week, for depression prevalence, incidence and mortality; the available evidence is insufficient to assess effects of the exposure. Producing estimates of the burden of depression attributable to exposure to long working appears not evidence-based at this point. Instead, studies examining the association between long working hours and risk of depression are needed that address the limitations of the current evidence.