Horror-movie buffs are familiar with the term, “blood-curdling scream”—you may have emitted a few in your time, especially if you’ve watched some of the 35 scariest movies of all time. But according to a group of Dutch researchers, no one realized how accurate the term “blood-curdling” is: Fear can literally cause your blood to curdle.
In the study, published in British journal The BMJ, researchers recruited 24 healthy volunteers aged 30 or younger. Fourteen of the volunteers watched a scary movie (Insidious), and then a week later a light, educational movie (A Year in Champagne). The remaining volunteers did the reverse, watching the tame movie first, and then the suspenseful one.
Researchers found that while watching Insidious, the volunteers’ levels of factor VIII—a protein that plays a role in blood clotting—jumped by enough to raise their risk of blood clots; 57 percent of the volunteers experienced the jump, while just 14 percent experienced an increase during the educational movie. If you prefer tear-jerkers over horror movies, it could be because sad movies actually make you happy.
There is a good chance we evolved the clotting response when we feel fear, according to Dr. Thomas E. Eidson DO, a vein disease specialist in Arlington, Texas. A blood clot is the body’s response to injury, and it can slow or stop bleeding. “Specifically, a blood clot is a combination of platelets in the blood combined with specific proteins in your blood to form a solid plug to prevent further bleeding.”
“When we are scared, the most primitive part of our brain takes over causing the flight-or-fight response,” explains Dr. Eidson. “Our body releases adrenaline, our pupils dilate, and our blood vessels in our extremities constrict moving blood to vital organs and muscles. The body also prepares itself by elevating factor VIII in the blood to increase the body’s ability to form clot in case of blood loss or injury.” This instinctive response doesn’t distinguish between being chased by a bear or watching a frightening movie, explains Dr. Eidson, so “it responds exactly the same.” Even more interesting is the fact that watching a horror movie actually burns calories. Here’s a list of the top 10 calorie burners.
However, the study authors concluded that the increase is unlikely to cause actual clot formation. So, grab the popcorn, hit the lights, says, Dr. Eidson: “You can enjoy watching Dracula and Night of the Living Dead knowing your body is primed to form a clot in case you scrape your shin on your coffee table jumping off the couch in fear.” Next, take a look at these healthy movies and documentaries to watch on Netflix.