Adverse Impact of Nonstandard Working Hours on Mental Health: An Analysis Using Two-way Fixed Effects Model

Although several studies have demonstrated the adverse impacts of both longer and shorter working hours on workers' mental health, findings remain inconsistent. This study aimed to analyze the impacts of working hours on mental health and investigate how this relationship varies across subgroups.

Using the 12th to 18th waves of the Republic of Korea Welfare Panel Study, we analyzed 29,025 observations from 7,415 individuals. Working hours were categorized as "<35 hours," "35-40 hours (standard)," "41-52 hours," and ">52 hours." Mental health outcomes included depressive symptoms, self-esteem, and subjective well-being. Two-way fixed effects models were used to analyze the causal associations between working hours, with subgroup analyses by gender, age, and employment type.

Compared to standard working hours, both reduced (<35 hours) and extended working hours (41-52 hours and >52 hours) were associated with adverse mental health outcomes. Depressive symptoms increased with reduced (estimate = 0.301) and extended hours (41-52 hours: estimate = 0.238; >52 hours: estimate = 0.283). Self-esteem decreased across all nonstandard categories (<35 hours: estimate = -0.266; 41-52 hours: estimate = -0.200; >52 hours: estimate = -0.214). Subjective well-being decreased with extended hours (41-52 hours: estimate = -0.054; >52 hours: estimate = -0.125). Extended hours were associated with adverse mental health across all groups, with stronger associations among women and younger adults. Women, older adults, and casual or fixed-term workers exhibited high vulnerability to the effects of reduced working hours.

Our findings indicate a nonlinear relationship between working hours and mental health, with standard working hours demonstrating the most favorable outcomes. Differential impacts across demographic groups underscore the necessity for tailored policies.