Objective: To assess whether, as has been hypothesised since medieval times, acute fear can curdle blood.
Design: Crossover trial.
Setting: Main meeting room of Leiden University's Department of Clinical Epidemiology, the Netherlands, converted to a makeshift cinema.
Participants: 24 healthy volunteers aged ≤30 years recruited among students, alumni, and employees of the Leiden University Medical Center: 14 were assigned to watch a frightening (horror) movie followed by a non-threatening (educational) movie and 10 to watch the movies in reverse order. The movies were viewed more than a week apart at the same time of day and both lasted approximately 90 minutes.
Main outcome measures: The primary outcome measures were markers, or "fear factors" of coagulation activity: blood coagulant factor VIII, D-dimer, thrombin-antithrombin complexes, and prothrombin fragments 1+2. The secondary outcome was participant reported fear experienced during each movie using a visual analogue fear scale.
Results: All participants completed the study. The horror movie was perceived to be more frightening than the educational movie on a visual analogue fear scale (mean difference 5.4, 95% confidence interval 4.7 to 6.1). The difference in factor VIII levels before and after watching the movies was higher for the horror movie than for the educational movie (mean difference of differences 11.1 IU/dL (111 IU/L), 95% confidence interval 1.2 to 21.0 IU/dL). The effect of either movie on levels of thrombin-antithrombin complexes, D-dimer, and prothrombin fragments 1+2 did not differ.
Conclusion: Frightening (in this case, horror) movies are associated with an increase of blood coagulant factor VIII without actual thrombin formation in young and healthy adults. Trial registration ClinicalTrials.gov NCT02601053.
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