The study, published in the journal sleep, provides evidence of the direct link between short duration of sleep (less than 6 hours sleep a night) and an increased chance of dying prematurely.

The research also notes that consistent over-long sleeping (over 9 hours a night) can be a cause for concern. While, unlike short sleeping, over long sleeping does not increase the risk of death, it can be a significant marker of an underlying serious and potentially fatal illnesses.

The study looked at the relationship between the level of habitual duration of sleep and mortality by reviewing 16 studies from the UK, USA, European and East Asian countries. The study included more than 1.3 million participants, followed for over 25 years, with more than 100,000 deaths recorded.

The study provides clear evidence of the direct link between both short (less than 6 hours sleep a night) and long (9 hours or more) duration of sleep and an increased chance of dying prematurely, compared to those who sleep 6-8 hours a night on average.

They pointed out that previous studies had shown that sleep deprivation was associated with heart disease, high blood pressure, obesity and type-2 diabetes.

The study author said "whilst short sleep may represent a cause of ill-health, long sleep is believed to represent more an indicator of ill-health."

He said: "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.

"Consistently sleeping 6 to 8 hours per night may be optimal for health. The duration of sleep should be regarded as an additional behavioral risk factor, or risk marker, influenced by the environment and possibly amenable to change through both education and counseling as well as through measures of public health aimed at favorable modifications of the physical and working environments. "

Research Paper Details:

Cappuccio FP, Elia L, Strazzullo P & Miller MA. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep, 2010; 33 (5).