Wednesday, June 24, 1998 Published at 19:17 GMT 20:17 UK
Nightmares: 'It's all in the genes'
Identical twins are twice as likely to have frequent nightmares
Nightmares have a genetic basis and are strongly linked to mental illness, scientists have discovered.
Finnish researchers base their claims on a study of the dreams of 2,276 pairs of identical twins and 4,172 pairs of non-identical twins.
According to New Scientist magazine, they found that identical twins are twice as likely to share the trait of having frequent nightmares as non-identical twins.
Nightmares raise the pulse rate and step up metabolism in the brain. The frequency of nightmares tends to stay roughly the same from childhood through middle age, with some people suffering three or four nightmares a week.
The research team, from the University of Helsinki, found that, if one of a pair of identical twins reported frequent nightmares - that is, three or more nightmares per week - there was a 45% chance that the other twin would share the same trait.
With nonidentical twins, there was only a 20% chance.
Researcher Christer Hublin said: "Your genetic constitution may make you more liable to nightmares."
More likely to be hospitalised
Examination of the volunteers' medical records showed that people who have frequent nightmares are 15% more likely to be hospitalised at least once in their lifetime for mental illness.
"We don't know if it's causative or co-occurring," said Dr Hublin.
Markku Partinen, another member of the team, noted that people with depression and schizophrenia reported more nightmares than healthy people.
He speculated that nightmares may be due to abnormal activity in the limbic system - the part of the brain that deals with emotions.