Background Long working hours are a risk factor for occupational health, particularly in labor-intensive sectors such as manufacturing. Prolonged working hours may have adverse effects on the sleep and mental health of employees.

Objective To investigate the impact of long working hours on insomnia, anxiety, and depression symptoms among manufacturing industry employees and provide scientific evidence for relevant occupational health interventions.

Methods A cross-sectional study was conducted involving 1524 employees from eight manufacturing enterprises in Shenzhen. Data were collected using a structured questionnaire, which included demographic characteristics, work conditions (e.g., years of employment, job type, shift work, night shifts, weekly working hours), personal behaviors (e.g., smoking and drinking habits), and the occurrence of insomnia (by the Athens Insomnia Scale), anxiety (by the Generalized Anxiety Disorder Scale), and depression (by the Patient Health Questionnaire). Participants were classified into two groups based on working hours: long working hours (≥55 h per week) and normal working hours (35-40 h per week). Binary logistic regression was used to analyze the association between long working hours and the occurrences of insomnia, anxiety, and depression symptoms.

Results A total of 1491 manufacturing industry employees were included in the study (response rate: 97.8%). The sample consisted of 54.19% males and 45.81% females, with the largest proportion was those aged 40-49 years (45.48%). The proportion of workers with long working hours in the total population was 31.52%, with the highest proportion among production and technical employees (36.49%). The prevalence of insomnia, anxiety, and depression symptoms was 56.2%, 26.6%, and 23.8%, respectively in the long working hours group, significantly higher than those in the normal working hours group (P<0.05). After adjusting for potential confounders, the logistic regression analysis showed that long working hours were significantly associated with increased risks of insomnia (OR=2.16, 95%CI: 1.60, 2.91), anxiety (OR=1.94, 95%CI: 1.34, 2.81), and depression symptoms (OR=1.62, 95%CI: 1.11, 2.38) compared to normal working hours.

Conclusion Long working hours significantly increase the risks of insomnia, anxiety, and depression symptoms among manufacturing industry employees. It is recommended that measures should be implemented to limit working hours, increase rest periods, and provide occupational health education and psychological support to improve the sleep and mental health of employees.