Trauma exposure can lead to posttraumatic stress disorder (PTSD) in a subset of vulnerable individuals. Circadian rhythm disturbances have emerged as a candidate pathway of vulnerability, yet mean circadian levels often show limited discriminability. We tested whether circadian instability at trauma aftermath prospectively predicts long-term PTSD risk, and what behavioral and physiological indices are most predictive. For that, 211 survivors of the Supernova music festival mass-trauma event and 113 matched comparison participants were monitored in real-world settings for one-month, two-to-six months post-event, using wearable sensors that tracked their heart rate (HR), activity, and sleep-wake cycles. PTSD symptoms were assessed before and after the recording period, as well as at follow-up eight-to-eleven months post-event. Linear regression models compared circadian metrics between trauma survivors and comparison participants, and tested associations between circadian measures two-to-six months post-event and PTSD status and severity at follow-up. Results revealed that trauma survivors exhibited reduced circadian stability relative to comparison participants, characterized by greater sleep interday instability and higher variability in daily HR acrophase, as well as elevated rhythm-adjusted mean HR (MESOR). Further, circadian instability at two-to-six months post-event was particularly elevated among survivors with PTSD at follow-up and predicted their symptom severity. Finally, hierarchical models highlighted sleep instability at trauma aftermath as the most significant circadian predictor of long-term PTSD risk, above and beyond initial PTSD severity. Together, specific behavioral and physiological metrics of circadian instability at trauma aftermath prospectively index PTSD risk, highlighting circadian regulation as a target for vulnerability monitoring and early intervention.
