Workers' experiences of improvements in the work environment and mental health problems: a web-based 1-year prospective study of Japanese employees.

Objectives: This study aimed to prospectively investigate the association between work environment improvements and multiple mental health outcomes in a large sample of Japanese employees.

Methods: A web-based longitudinal study surveyed 20 000 Japanese employees, 7970 of whom completed a follow-up after 1 year. Various types of work environment improvements experienced by workers were assessed using a 24-item checklist. Three mental health outcomes (poor mental health, presenteeism, and high psychosocial stress) were assessed and defined using standardized questionnaires.

Results: Overall, as the total number of work environment improvements increased, the odds ratio for mental health outcomes in the follow-up survey decreased by several percentage points, even after adjusting for demographic and occupational factors. Analysis of the types of work environment improvements showed that mutual support improvements were particularly effective in reducing mental health issues. The subgroup analyses also showed that the effectiveness of workplace environment improvements might vary between secondary and tertiary industry workers depending on the types of improvements and mental health outcomes.

Conclusions: The study suggests that workplace improvements can significantly affect mental health. The effectiveness of these improvements may vary according to the type of intervention, industry of the targeted workers, and mental health outcomes. This study provides basic data on the effectiveness of workplace environment improvements that can be used for future intervention trials.