This is the short edition of More or Less, first broadcast on the BBC World Service.

Hello and welcome to more or less on the BBC World Service.

I'm Ruth Alexander.

This week, could having long lie-ins kill you? I try, although often

fail to get eight hour sleep, which I always thought was the ideal. That is not true.

Until I heard from Dr. Greg Jacobs,

a specialist at the Sleep Disorder Center

at the University of Massachusetts Medical School in the US.

We were given that recommendation for many years and now the research over the past 10 years suggests that sleeping eight hours a night may be a health risk.

So Greg believes that getting eight hours sleep a night might actually be bad for you.

There have been about 34 studies. These are epidemiologic studies that follow people over time, involving over 2 million people

that consistently show that there's a U-shaped relationship between sleep duration and mortality.

The lowest mortality is at the bottom of the U and that's seven

hours of sleep and then as you sleep less than seven or more than seven there's a

gradual increase in mortality risk with long sleepers and short sleepers showing the greatest increase in mortality.

Of course we're all going to die one day so what's meant by increased mortality risk?

Well it means you've got more chance of

dying sooner rather than later, and more on that shortly, but first let's find out

more about how our sleep habits are studied. Although some studies have shown that 8 hour sleep is associated

with health problems, we probably shouldn't talk about 8 hours so precisely in

the view of Franco Capuccio, a professor of cardiovascular medicine and

epidemiology at the University of Warwick in the UK, he's done a detailed analysis of

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