The Fukushima Nuclear Energy Workers' Support (NEWS) Project Study previously showed that experiences related to the Fukushima nuclear disaster on 11 March 2011 had a great impact on psychological states, including post-traumatic stress response (PTSR) and general psychological distress (GPD), among the Fukushima nuclear plant workers. To determine the causal relationship between disaster-related experiences and levels of psychological states, we conducted a 3-year longitudinal study from 2011 to 2014.

PTSR and GPD of the nuclear plant workers were assessed by annual questionnaires conducted from 2011 to 2014. The present study included a total of 1417 workers who provided an assessment at baseline (2011). A total of 4160 observations were used in the present analysis. The relationship between disaster-related experiences and psychological states over time was analysed using mixed-effects logistic regression models.

A declining influence of disaster-related experiences on PTSR over time was found. However, the impact on PTSR remained significantly elevated even 3 years after the disaster in several categories of exposure including the experience of life-threatening danger, experiences of discrimination, the witnessing of plant explosion, the death of a colleague and home evacuation. The associations between GPD and disaster-related experiences showed similar effects.

The effects of disaster-related experiences on psychological states among the nuclear plant workers reduced over time, but remained significantly high even 3 years after the event.