Dr Sara Gottfried is, in her own words, an "under sleeper". In our over-caffeinated, over-worked and gadget-addicted society, she's far from alone: researchers from Oxford, Cambridge, Harvard, Manchester and Surrey universities have found people are sleeping almost two fewer hours a night than they were in the 1960s - and our health is deteriorating as a result.

"We are the supremely arrogant species; we feel we can abandon four billion years of evolution and ignore the fact that we have evolved under a light-dark cycle," says Oxford University's Professor Russell Foster, who worked on the study.

"What we do as a species, perhaps uniquely, is override the clock. And long-term acting against the clock can lead to serious health problems." These problems include an increased risk of cancer, heart disease, type-2 diabetes and obesity.

"Under-sleeping is the next sugar - it's a health time bomb," says Dr Gottfried, who says just about every aspect of modern living is stealing our sleep. "Our lives are more hectic than ever, more people live in cities where they're less attuned to light-dark cycles, we binge-watch TV shows, tablets emit sleep-disrupting blue light all evening, and it's become normal for our bosses to email us at 9pm (they never could 20 years ago). What it means to be available has changed and our sleep is suffering.

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"Screens aren't the only culprits either - ecological fluorescent light bulbs or LED lights emit more blue light than old-school light bulbs."

Dr Gottfried says artificial light has a hugely disruptive effect on our body clocks. Linked to our circadian rhythm, which regulates cell regeneration, brainwave activity, hormone production and the regulation of glucose and insulin levels, it naturally adjusts to daylight and darkness. To stay healthy, we should still be sleeping like our ancestors by going to bed at sunset and waking at sunrise - a pattern all but dispensed with in the modern world.

"If we deprived ourselves entirely of sleep we wouldn't live much longer than if we deprived ourselves of water, and five times quicker than if we stopped eating", says sleep consultant Dr Neil Stanley. "In over one million years of evolution, our sleep needs remain the same."

How much shut-eye do we actually need?

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This Friday, March 17, is World Sleep Day - so there's never been a better time to ask the question.

"The eight hour thing is a myth," says Dr Stanley. "Sleep needs are like height - different for everybody and down to genetics. Just like there are tall and short people, there are people who need fours hours a night and others who need 11. You cannot train yourself to need less sleep and if you frequently go without your required hours you'll do yourself harm."

"The way to tell if you are getting enough is simple, he says. "If you feel awake and alert during the day, yes. If you feel sleepy in the day, no. And there's a difference between feeling tired and feeling sleepy; the latter means literally wanting to sleep during the day."

The ramifications of insufficient sleep are quickly felt: studies show that just one night without proper rest quadruples your risk of catching a cold. It "suppresses immunity. You'll have less motivation, less empathy, slower reaction times, poor concentration and increased appetite," Dr Stanley adds.

Researchers from Pennsylvania State University found getting fewer than six hours' sleep a night causes your levels of the hormone ghrelin, which signals hunger, to go up and levels of leptin, the sense of fullness hormone, to drop. When you're tired you'll feel hungry, then, but never full.

"Long term, regularly shaving an hour or more off your required sleep increases your risk of certain cancers, diabetes, Alzheimer's, obesity, cognitive decline, depression and heart disease." A study from Harvard Medical School found that people who sleep fewer than five hours a night for five consecutive years have a 300 per cent greater risk of hardened arteries. "There is not one single good thing about poor sleep,' says Stanley, "yet we live in a society that at best disregards it and at worst, views getting by on very little as a badge of honour."

Do you have the short-sleep gene?

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Dr Gottfried says that while you may think you can get by on little sleep, the truth is only three per cent of the population has the short-sleep gene (known as DEC2). "I would stay up for 36 hours at a time during my medical training, surviving on coffee," she recalls. "But coffee - like anything else that delays sleep - is a high interest loan and eventually your body will call that loan in."

Gottfried says the brain is the organ most impacted by poor sleep and that in the last ten years neuroscience has shown a lack of the stuff can both change and age your brain. Good sleep, however, 'shampoos' your brain and 'washes away' ageing toxins.

"During sleep, the space between brain cells expands 60 per cent more than when you're awake," she says. "This allows the brain to flush out built-up toxins with cerebral spinal fluid, the clear liquid surrounding the brain and spinal cord. It's called the glymphatic system and this system works better when you're sleeping on your side, rather than back or tummy."

Then of course there's ageing; according to research from the Harvard School of Public Health sleeping five or fewer hours a night equates to ageing an extra four to five years.
"There's a reason it's called beauty sleep," says Dr Gottfried. 'From personal experience it's pretty dramatic how different my face looks when I'm tired. I look more pale and my face becomes puffy.'

Can you play catch-up with sleep?

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So can a Sunday morning lie-in repay the sleep debt of the tumultuous week beforehand?

"Yes, but it requires a mindset change," says Dr Gottfried. "In the past, I've racked up gigantic sleep debts and have gained weight, become stressed and felt stiff and older than my years as a result. Now I view sleep as a non-negotiable and even though I have two children, a husband and a job, I no longer 'steal' from my sleep in order to fit everything in."

She says little and often is key with repaying sleep debt rather than trying to catch up in one large chunk, as binge sleeping disrupts your body clock. "Naps also help and a 20-minute daytime nap is the equivalent of an hour at night." Another tip is batch cooking: "Every working person will know that cooking a fresh meal in the evening - and washing up afterwards - cuts into sleep. So now I soften my expectations and grab something quick, or I batch cook and eat heated leftovers. This small thing gives me an hour more sleep every night of the week."

Dr Guy Meadows, Clinical Director of The Sleep School says; "A small sleep debt is easily repaid with an early night. But if you've raised children, travelled a lot for work or suffered with insomnia, you'll have a bigger sleep debt. Worse still, you may have become a bad sleeper, which makes the debt bigger.

"I tell the bad sleepers in my sleep clinic to stop chasing sleep, as this drives it further away. If you ask a great sleeper how they get to sleep, they'll say 'nothing'. If you ask a bad sleeper how they do it, they'll give you a long list that includes warm baths and lavender pillow mist. My theory is that often the ways we try to chase or control our sleep is part of the problem. Try to be almost thoughtless about it.

"Sleep is what makes us brilliant because it's the most natural powerful performance enhancer known to humankind. It's time we started treating it as such."

Sleep smarter | Forty winks in seven steps

1.

Prioritise your pre and post sleep routines as they directly affect the quality of your sleep and waking day.

2. Take technology breaks during the day as a reward and training for body and mind.

3. Get up earlier than you need to. Take a full 90 minutes to prepare for your day.

4. Don't reach for the phone! Raise your alertness before you send your first text message or reply to that email.

5. Moving your body from warm to cooler helps trigger the natural drop in body temperature you need to sleep well. A quick warm rinse under the shower and a cooler sleeping environment will help.

6. Declutter your bedroom and mind before you attempt sleep.

7. Go from light to dark in the evening and darkness to light in the morning in an unrushed way.

Younger by Dr. Sara Gottfried is published by Vermillion. Order a copy for $24.83 from Paper Plus or a digital copy for $17.99 from iTunes Apple store.
This article was originally published by The Telegraph.