Synergistic Effect of History of Cardiovascular Disease and Mental Distress on Post-Traumatic Stress Disorder after the Great East Japan Earthquake: The Fukushima Health Management Survey

Cardiovascular disease (CVD) and mental distress have been suggested to be associated with post-traumatic stress disorder (PTSD), but the effect of their combination on PTSD is unknown. We reviewed the synergistic effects of the history of CVD and mental distress on the possibility of PTSD among residents in Fukushima after the Great East Japan Earthquake. This cross-sectional study was conducted among 38,392 participants aged 40–74 years in the evacuation area who applied for the Fukushima Health Management Study in Fiscal Year 2011. Relative excess risk due to interaction (RERI), attributable proportion (AP), odds ratio (OR), and 95% confidence interval (CI) were calculated to investigate the combined effect of history of CVD and mental distress on PTSD. We identified 8104 probable cases of PTSD (21.1%). History of CVD, mental distress, and their combination were positively associated with probable PTSD: the multivariable ORs (95% CIs) were 1.44 (1.04, 2.01), 20.08 (18.14, 22.22), and 26.60 (23.07, 30.67), respectively. There was a significant increase in RERI: the corresponding RERI (95% CI) and AP were 6.08 (3.16, 9.00) and 22.9%. Gender-specific analyses showed similar associations. Thus, we found a supra-additive association of history of CVD and mental distress with probable PTSD after the disaster.