Sleeping less than six hours a night increases the risk of early death, it was claimed today.
Scientists arrived at the result after analysing data from 16 studies involving more than 1.5 million participants.
They found "unequivocal evidence" of a direct link between sleeping less than six hours a night and dying prematurely.
People who regularly had this little sleep were 12% more likely to die over a period of 25 years or less than those who got the recommended six to eight hours.
An association was also seen between sleeping more than nine hours a night and early death. This was thought to be due to long-sleeping being a marker of serious underlying illness rather than any effect of sleep itself.
Professor Francesco Cappucio, head of the Sleep, Health and Society Programme at the University of Warwick, said: "Whilst short sleep may represent a cause of ill-health, long sleep is believed to represent more an indicator of ill-health.
"Modern society has seen a gradual reduction in the average amount of sleep people take, and this pattern is more common amongst full-time workers, suggesting that it may be due to societal pressures for longer working hours and more shift-work. On the other hand, the deterioration of our health status is often accompanied by an extension of our sleeping time."
The research, reported in the journal Sleep, reviewed 16 prospective studies from the UK, US, Europe and Asia which together monitored more than 1.3 people for up to 25 years.
In total, more than 100,000 deaths were recorded during the observation periods.
Pooling together data in this way, known as meta-analysis, can indicate patterns and trends that may not be obvious in individual studies.
Prof Cappucio, who worked with colleagues from the Federico II University Medical School in Naples, Italy, added: "Consistently sleeping six to eight hours per night may be optimal for health.
"The duration of sleep should be regarded as an additional behavioural risk factor, or risk marker, influenced by the environment and possibly amenable to change through both education and counselling, as well as through measures of public health aimed at favourable modifications of the physical and working environments."
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