The word ‘bloodcurdling’ is often associated with horror movies, but a new study has shown it is legitimately associated with an increase in a blood clotting protein called Factor VIII. Watching horror movies really can thicken your blood!

The small study from the Netherlands was published in the British Medical Journal’s Christmas edition, which is often reserved to showcase quirky or humorous medical research.

The word ‘bloodcurdling’ was first noted back in medieval times and arose from the belief that fear could curdle or thicken the blood. The Dutch research team wondered if there was a genuine basis for the belief, which they thought could confer a health benefit by preparing the body for blood loss during life threatening injuries.

24 healthy volunteers were divided into two groups. The first group watched a horror movie, waited a week and then viewed a documentary, whilst the second groups watched the same films but in the reverse order. Blood was drawn immediately before and after each film viewing and a pathology laboratory tested the clotting factors.

The clotting factor level increased in 57% of participants during the horror movie, but only in 14% of participants when watching the documentary.

The body’s ability to form blood clots is balanced by an intricate web of compounds called clotting factors. Some promote clotting whilst others prevent it. Blood clots can be useful at times, particularly to stem blood loss in major injury. However, when they form internally and without need they can be lethal, as with strokes.

Pathology laboratories help patients with clotting disorders by monitoring the levels of clotting factors. Levels can be affected by genetic conditions meaning they naturally have high or low levels of specific factors. It can also be affected by certain surgical procedures. Some patients need to placed on blood thinning medication such as warfarin.

Regular blood testing is a vital part of healthcare for these patients, allowing them to live their normal lives knowing that their blood is at a safe thickness.