All of which suggests that Boris Johnson, London's mayor, has his work cut out to fulfil his pledge that, by the end of 2012, no one will live on his city's streets, and no one landing there will sleep out for a second night.

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After many years of study, no one knows how much sleep we need to function normally.

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But no one is allowed to sleep there overnight, and the group's meetings have migrated to indoor spaces.

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For example, you might consider a limit of one or two hours a day and, for a better night's sleep, no screen time in the hour before bed.

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Mr Gill stayed in hospital with his wife and, with no other facilities available to him, had to sleep on the floor which he described as "one of the hardest night's sleep".

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No one, not even museum curators, could say whether the thin, mostly immobile Swinton is actually getting some sleep while people stare at her.

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The Flex tracks your sleep quality as well, but the approach here differs from other Fitbit products: whereas the Fitbit One and Fitbit Zip have a key you can press to enter sleep mode, the Flex has no buttons at all, so your only recourse for logging sleep is to use the app or website.

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While no one will dispute the fact that many of our current habits concerning food consumption, physical activity, stress management and sleep deprivation could use some positive invigoration.

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