Lack of sleep linked to early death

Getting less than six hours sleep a night can lead to an early grave, UK and Italian researchers have warned.
They also found an association between sleeping for more than nine hours and early death, although that much sleep may merely be a marker of ill health.
Sleep journal reports the findings, based on 1.5m people in 16 studies.
The study looked at the relationship between sleep and mortality by reviewing earlier studies from the UK, US and European and East Asian countries.
Premature death from all causes was linked to getting either too little or too much sleep outside of the "ideal" six to eight hours per night.
Interesting... I understand why lack of sleep can be linked to early death, but sleeping for more than 8 hours...?