Albert Einstein was said to sleep for 11 hours
Margaret Thatcher famously survived on only four hours a night, while Albert Einstein needed almost three times as much.
Now a study by scientists at Edinburgh University has suggested the reason some people need more sleep than others is all in the genes.
Researchers discovered a variation of a gene called ABCC9, which they think helps explain why some people need more shut-eye.
One in five Europeans carry the variant of ABCC9, which is involved in sensing energy levels of cells in the body.
Those with the ‘sleep switch’ needed almost 30 minutes more rest each night than those without.
Experts hope the finding will help future sleep studies establish how the gene variant regulates sleep duration.
Edinburgh scientists worked alongside researchers from Ludwig Maximilians University Munich to study genes in fruit flies and human sleep patterns.
Flies without the ABCC9 variant slept for three hours less than normal, while humans with it slept for longer than the ‘average’ eight hours.
More than 10,000 people throughout Europe – including 1,000 Scots – took part in the study, providing information on how many hours they slept each night and a blood sample to analyse their DNA.
Sleep was measured on ‘free days’ – when people did not need to get up for work the next day, take sleeping pills or work shifts.
Dr Jim Wilson, of Edinburgh University’s Centre for Population Health Sciences, said sleep plays a hugely important role in our health.
He added: ‘I was staggered when we found this gene variant, given the obvious health difficulties people suffer as a consequence of a lack of sleep.‘You have to understand a problem before you can do something about it. Hopefully more genes will now be discovered and this can also lead to us dealing better with the connected health issues.’
Researchers also found the length of time people slept for often ran in families, despite the fact that the amount of sleep people need can be influenced by age, latitude, season and circadian (24 hour) rhythms.
Dr Wilson said he believed the study would help reveal the health effects of different sleep behaviours.
He added: ‘I don’t think it’s as simple as people with the gene going to bed 30 minutes earlier but today we are a step closer to tackling the problems for people who struggle to sleep.’
The paper is published online in Molecular Psychiatry.