Abstract
Background : Atypical working hours (AWH) encompass night work, rotating shifts, permanent night schedules, long working hours, weekend work, on-call duty, and irregular schedules. AWH are prevalent across healthcare, manufacturing, transport, and service sectors. The 2016 expert appraisal by the French Agency for Food, Environmental and Occupational Health and Safety (ANSES) provided a landmark classification of health outcomes associated with night work, but the evidence base has expanded substantially since that appraisal through systematic reviews, meta-analyses, and umbrella reviews.

Objective : The aim of this study was to update the ANSES 2016 risk classification for night work and rotating shift work using post-2016 review-level evidence, and to synthesize and classify evidence for other atypical working hours (long working hours, weekend work, irregular schedules) using transparent criteria informed by GRADE principles.
Methods : We conducted a structured narrative review with a systematic search, following PRISMA 2020 guidelines. PubMed/MEDLINE was searched for review-level evidence from January 2016 to March 2026. Backward citation searching and manual retrieval from ANSES, IARC, and WHO/ILO complemented the database search. Eligibility required sources to be systematic reviews, meta-analyses, umbrella reviews, or authoritative reports on adult working populations exposed to AWH. We excluded non-occupational studies, conference abstracts, protocols, and redundant syntheses. Health outcomes were classified as Established, Probable, or Possible based on consistency, study design quality, dose-response evidence, and biological plausibility. In total, 29 review-level evidence syntheses and 4 authoritative reports were included.
Results : The strongest post-2016 evidence indicates adverse associations of night and shift work with sleep and circadian disorders, metabolic syndrome, overweight, obesity, cardiovascular disease, and depressive symptoms. Elevated risks also include type 2 diabetes, hypertension, dyslipidemia, suicidal ideation, and pregnancy complications. Long working hours of 55 or more per week are linked to higher risks of stroke and ischemic heart disease. Breast cancer evidence is limited to subgroups with persistent high-intensity night work. Associations with prostate and colorectal cancer, musculoskeletal disorders, cognitive decline, and chronic kidney disease are suggestive but more heterogeneous, with lower certainty. Important modifiers include sex, chronotype, the co-occurrence of night work with long working hours, and geographic underrepresentation of low- and middle-income countries.
Conclusions : The evidence confirms AWH as a significant occupational health exposure needing systematic prevention. Compared to the 2016 framework, cardiometabolic and some mental health outcomes need upgraded classification, while cancer-related and emerging outcomes require careful interpretation. Research priorities include harmonized exposure definitions, sex-specific analyses, joint quantification of night work and long hours, broader geographic coverage, intervention studies, and investigation of long-term risk reversibility.

Key words: atypical working hours; shift work; night work; long working hours; circadian disruption; occupational health; risk classification.