Can watching a scary movie be GOOD for your health?

There's a range of explanations for why horror fans seek out shock, says psychologist Mark Griffiths, a professor of behavioural addiction at Nottingham Trent University.

'It may be about experiencing things we never would in our day-to-day life,' he says. 

Watching such films 'may also be cathartic, providing an emotional release for pent-up frustrations'.

But is all that leaping out of your skin doing you any good? Strangely enough, some research shows it could be.

For example, there is evidence that watching a terrifying film can boost your immune system temporarily.

Researchers at Coventry University took blood samples from volunteers before, during and after sitting quietly in a room or watching a horror film. 

In a paper published in the journal Stress, they reported that levels of white blood cells, usually boosted in response to infection, were increased.

This is the result of a process honed by years of evolution that is 'geared to promote the survival of the individual', says Natalie Riddell, an immunologist at University College London. 

Watching a horror film 'triggers the fight-or-flight response,' she says, and this releases the hormone adrenaline.

In turn, adrenaline mobilises your immune system. 

The adrenaline also raises your heart rate and increases the body's metabolic rate, the speed at which stored energy is consumed — so watching horror films could also help with weight loss. 

A 2012 study by the University of Westminster measured how many calories were burnt by volunteers watching ten horror classics. 

On average, each film burnt 113 calories, equivalent to a 30-minute walk. But the best film was 1980's The Shining, which scared off 184 calories — the same as a Crunchie bar.

There is also evidence that horror movies could be good for your love life — and even make less attractive men more appealing to women.

Researchers at Indiana University paired 36 male and 36 female students to watch the 1982 slasher movie Friday The 13th Part III.

They reported in the Journal of Personality and Social Psychology in 1986 that men liked horror more than women and enjoyed it most 'in the company of a distressed woman' and least 'in the company of a fear-mastering woman'. For women, the opposite was true.

In what became known as the 'Snuggle Theory', they concluded 'men not equipped with an irresistible physique . . . gained markedly in sexual appeal'.

But it's not all good news for horror fans. This summer, there were rumours that more than 30 people had dropped dead watching The Conjuring 2. 

In fact, it seems only one 65-year-old man in India died watching the film — though, in a ghoulish twist, his body vanished before a post-mortem could be carried out.

However, it is possible for a horror film to scare you to death by causing a cardiac arrest as a side-effect of the fight-or-flight response.

'Stress of any description leads to increased production of adrenaline, which causes blood vessels to constrict and the heart to work harder and faster,' says Andrew Lockey, a consultant in emergency medicine at Calderdale & Huddersfield NHS Trust and honorary secretary of the Resuscitation Council (UK).

'If someone has an underlying heart problem, then a large surge of adrenaline can be dangerous.'

Horror can be heart-stopping in other ways. Cardiologists at the University of Maryland in 2005 found watching the gruelling opening of Saving Private Ryan caused the endothelium, tissue that lines blood vessels, to constrict — reducing blood flow and raising blood pressure. Again, this is an effect of adrenaline.

Another study found horror films can, literally, be blood-curdling. 

Researchers at Leiden University in the Netherlands took blood samples from 24 people before and after a horror film and reported in the BMJ in 2015 that it led to increased production of blood-clotting protein Factor VIII to a level linked with increased risk of blood clots — possibly because thickening the blood is the body's way of bracing for anticipated heavy bleeding.

This, says Natalie Riddell, is an effect of evolutionary conditioning: we know the man isn't coming for us with a chainsaw, but instinctively the body braces itself just in case.

Watching scary movies can also make your hands cold, say scientists at Kyushu University in Japan, who found that as fear rose, the temperature in fingertips fell.

This is thought to be the result of the fight-or-flight response, re-routing blood from the extremities to where it may do more good, such as the heart and muscles.

This 'fear-induced sympathetic response' also explains why you get goosebumps and start looking over your shoulder while watching a scary film. 

But then again, maybe there really is something behind you...

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