Dreamland is a much scarier place for blind people, with new research indicating that those born blind have four times as many nightmares than sighted people.

After a four-week examination of 50 people, 25 of whom were blind, Danish sleep scientists reported that 25% of dreams experienced by those people born-blind are nightmares.

Sighted people, on the other hand, have nightmares only 6% of the time, and those who became blind later in life are said to suffer nightmares 7% of the time.

"At the core of my nightmares is a feeling of complete helplessness," 41-year-old Heidi Andersen, who was born blind, told Science Nordic.

The study's lead-author Amani Meaidi, from the Danish Centre for Sleep Medicine at Glostrup Hospital and BrainLab at the University of Copenhagen, said: "The study confirms an already existing hypothesis that people's nightmares are associated with emotions they experience while awake.

"And blind people apparently experience more threatening or dangerous situations during the day than people with normal sight."

Some participants dreamed of embarrassing social situations, others were victims in a car crash.

The nightmares were often related to threats experienced in everyday life.

Meaidi also said that the study concluded that dreams are a largely sensory experience, a way for the brain to process the day's sensual experiences.

"The study also points out that the sensory input and experiences we get while awake are decisive when it comes to what we dream.

"So people without visual sensory input dream to a much greater extent in terms of sounds, tastes, smells, and touch."

People who are born blind did not have dreams with visual content, whilst those who became blind later in life reportedly progressively less visual dreams.

Meaidi said: "Because people who lose their sight later in life have previously seen their surroundings it might be that their brains do not experience being threatened by circumstances to the same degree as people who are born blind.

"For this reason they may not need to process impressions from everyday life to the same extent by means of nightmares."

All of these discoveries were surprising to the blind test subjects, who were unaware that they had a disproportionate number of nightmares.

"This isn't something that causes problems for them in their everyday lives, for which reason several of them are surprised to hear the result," says Maeidi.

He stressed that the study also found that blind-from-birth people are not especially prone to anxiety or depression, or even that they had more negative emotions than sighted people.