Aim: The Fukushima disaster was caused by an earthquake that occurred on 11 March 2011. Following the serious damage caused by the earthquake and the subsequent tsunami, radioactive contamination occurred because of the meltdown accident at the Fukushima nuclear power plant. We investigated what mental disorders were likely to become exacerbated under these conditions.
Methods: We surveyed psychiatric outpatients at Fukushima Medical University Hospital for 1 month (31 days) from the day of the earthquake (March–April 2011).
Results: The survey revealed that bipolar I disorder was most likely to become exacerbated under the conditions and that the exacerbation exhibited was more likely to involve manic switches than depression.
Conclusion: On the basis of the results of our study, particular care must be taken to follow up bipolar I disorder patients after a natural disaster. Our results also suggested the possible origin of bipolar I disorder.