Objectives We studied the association between long working hours and decreased kidney function, which was determined using estimated glomerular filtration rate (eGFR), among the working population in South Korea.

Methods We analysed nationally representative cross-sectional data for 20 851 Korean workers ≥20 years of age. A negative binomial regression model was used to test differences in the prevalence of chronic kidney disease (eGFR <60 mL/min/1.73 m²) among workers divided into groups according to weekly working hours (<30, 30–40, 41–51 and ≥52 hours/week). Multivariate linear regression analysis was performed to investigate the association between weekly working hours and eGFR, with adjustments made for age, sex/gender, income, education, shift work, occupation, smoking, alcohol use, hypertension, diabetes mellitus, body mass index, systolic blood pressure, fasting blood glucose and total serum cholesterol.

Results A 1-hour increase in weekly working hours was associated with 0.057 mL/min/1.73 m² (95% CI 0.005 to 0.109) decrease in eGFR among participants who worked ≥52 hours/week. Among participants without hypertension or diabetes, a 1-hour increase in weekly working hours was significantly associated with 0.248 and 0.209 mL/min/1.73 m² decrease in eGFR among participants who worked 30–40 hours/week and 41–51 hours/week, respectively.

Conclusion Long working hours are associated with decreased kidney function. We expect that our findings could call for more research regarding this association and provide policy-oriented perspectives.