Those few extra hours you think you need could be because of genes
People who like to spend their spare time in bed asleep, may now have an excuse - it's partly down to their genes, according to experts.
But it now appears that some people may need more sleep than others because they carry a certain gene variant.
Margaret Thatcher famously survived on only four hours a night, while Albert Einstein needed almost three times as much.
Scientists at Edinburgh University discovered a variation of a gene called ABCC9, which results in some people needing 30 minutes extra each night.
One in five Europeans carray a variant of the gene, which is involved in sensing energy levels of cells in the body.
Dr Jim Wilson, from the University of Edinburgh's centre for population health sciences, said: "Humans sleep for approximately one-third of their lifetime.
"A tendency to sleep for longer or shorter periods often runs in families despite the fact that the amount of sleep people need can be influenced by age, latitude, season and circadian rhythms.
"These insights into the biology of sleep will be important in unravelling the health effects of sleep behaviour."