IF you toss and turn at night struggling to nod off, you may think stress is to blame for your whirring brain.
But the real explanation may lie deep within your genetic make-up.
A Dutch study has identified seven genes that put people at increased risk of developing sleeplessness.
Their discovery, that a tendency to suffer sleep problems is biological, rather than psychological, is a whole new approach and gives hope to the third of UK adults who have sleep problems.
It means that targeted treatments could be developed, rather than the ten million prescriptions for sleeping tablets which are made each year.
The research, by scientists at Vrije University in Amsterdam, was carried out by mapping the DNA of more than 113,000 people from Britain and the Netherlands.
Sleep specialist Professor Eus Van Someren said: "Insomnia is all too often dismissed as being "all in your head"."
"Our research brings a new perspective. Insomnia is also in the genes." The professor, whose work is published in the Nature Genetics journal, said he hoped the breakthrough will lead to far more research into sleep problems, which he said has been neglected in the past.
"As compared to the severity, prevalence and risks of insomnia, only few studies targeted its causes," he said.
The team also discovered there are different genetic mutations linked to sleep for men and women and if you are female, you are more susceptible to the problem.
They also found a strong genetic overlap with other traits such as anxiety disorders, depression and neuroticism, and low well-being.
Anke Hammerschlag, a PhD student at Vrije University, said: This is an interesting finding, because these characteristics tend to go hand in hand with insomnia.
"We now know this is partly due to the shared genetic basis."
Professor Danielle Posthuma, also at Vrije University, said there are also separate variants for men and women. She explained: "Part of the genetic variants turned out to be different. This suggests that, for some part, different biological mechanisms may lead to insomnia in men and women.
"We also found a difference between men and women in terms of prevalence: In the sample we studied, including mainly people older than 50 years, 33 per cent of the women reported to suffer from insomnia. For men this was 24 per cent."
The risk genes were tracked down thanks to the UK Biobank, a health study which has recruited half a million people aged 40 to 69 and makes data on DNA available.
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