Can we sleep for less than eight hours a night and still stay healthy? I've never questioned this much-trusted figure, until I met Topher Gaylord, an ultradistance runner specialising in 100-mile mountain races.
His training schedule would make most of us weep, but he combines it with only a few hours of sleep a night and still manages a 70-hour working week. You have to wonder how he does it. "Maybe I'm unusual but I can operate well, for work and running, on five hours' sleep a night for months," says Topher, who runs an outdoor clothing company.
He is one of a growing band of "sleep hackers", who manipulate their sleep for a particular given aim, normally to reduce the time spent sleeping while still getting the necessary amount of rest. The most extreme hackers (a predominantly male obsession) are the "polyphasic", multiphase, sleepers, who have cut their sleep to just two hours daily, taken in six 20-minute naps. By all accounts, the transition to this mode of sleeping is horrific, but most claim great physical and mental function and even increased alertness and well-being.
Polyphasic sleep is possible because of the three key phases of sleep: light, deep and REM (rapid eye movement). While deep and REM sleep provide the most restorative properties, light sleep takes the lion's share of time. It's this light sleep that hackers look to eliminate.
Medically, however, the jury is out on how far light sleep can be sacrificed, and when it comes to reducing it to two hours a day "you're a danger to yourself and your body," says Adrian Williams, professor of sleep medicine at King's College London.
"Just over eight hours is the average amount of sleep needed for 95 per cent of the population. We tend to shorten the time we give ourselves to sleep, but you cannot shorten the amount you genetically need."
It seems the way in which we sleep is hereditary. EEG (electroencephalography) scans of family members have shown there are remarkable similarities in sleep patterns. There's even a gene for short sleepers and perhaps Topher Gaylord is one of the lucky few with that gene. I doubted I was similarly blessed, but realising I could gain an extra month a year by cutting my nightly sleep from eight to six hours, I decided to find out. Which is why I am lying here strapped to an odd piece of kit at the Sleep Disorders Unit in St Thomas' Hospital, London.
The Zeo Sleep Manager is a small headband which connects to an app on your smartphone via Bluetooth and records the electrical signals naturally produced by the brain at night. It takes some getting used to: it's a pretty daft look for a start, the headband falls off in the night, and having to fiddle with your phone settings to get it running at bedtime is hardly restful. But, once operational, the results are fascinating. Not only does it record your sleep stages, it then advises you how to improve your sleep.
It's a sleep hacker's dream, but in my case it turned out to be a nightmare. The results were erratic at best. When, after a month, I still hadn't achieved the required seven nights' clear data to allow me to move onto fine-tuning my sleep, I gave up on the Zeo.
There followed experiments with an app called Sleep Cycle, which wakes you up in light sleep to ease morning grogginess (a bargain, but ditched due to it requiring a live phone under your pillow all night). Then there was the Sleeptracker Elite watch, which mirrored the Sleep Cycle but without the need for the phone (ideal, except that it failed to wake me). Finally I tried a Lumie Bodyclock Go 75 dawn simulator. This worked well for a fresh wake- up, but by this stage my enthusiasm for the project had been exhausted.
I was tired, irritable and sleeping worse than ever thanks to this endless gadget testing. Travelling had become bogged down in a sea of chargers, cables and gizmos, while the pressure of data collection and the frustration of oversleeping dogged peaceful nights at home.
So, after two utterly unsuccessful months, I conceded that while six-hour nights may be good for some, I clearly wasn't one of them. I called my experiment off, hit the snooze button and returned to eight hours. Bliss.