Roxy Jacenko wears many (designer) hats. She runs a successful PR company in addition to a number of other businesses, is a mum of two and a social media influencer in her own right.

How does she find the time? Well, now we know.

She recently told Kyle and Jackie O exactly how much sleep one of Australia’s most successful businesswomen really needs.

“I don’t really sleep that much. I get four hours… I’m probably a miserable b*tch but that’s just how it is,” she said.

Bring your daughter to work day – shoot time ????

A post shared by Roxy Jacenko (@roxyjacenko) on Nov 15, 2017 at 4:13pm PST

When compared to many people with demanding jobs, Jacenko’s minimal sleep time is almost the norm.

Former British Prime Minister Margaret Thatcher trained herself to get just four hours sleep a night, while Kevin Rudd once claimed he survived on only three hours sleep. Former real estate mogul and current US president Donald Trump also famously said he only needs four hours kip every night. (On a side note – perhaps that explains a lot?)

Given the recommended amount of sleep is 7.5 to eight hours a night, how is it possible to function on so little?

Turns out that while it can be damaging for some people, for others it’s perfectly normal.

Listen: Why sleep is so important. (Post continues after audio…)

“There are individual differences in how long people sleep and there is such thing as short sleeper syndrome where people habitually get less than four hours sleep,” explains Professor Dorothy Bruck, Chair of the Sleep Health Foundation.

It’s a sort of genetic mutation that allows people to survive on reduced amounts of sleep with no ill health effects.

“You can’t train yourself to do this but some people have this genetic mutation and can survive on less sleep,” Professor Bruck says.

“Though for most people sleeping less than six hours has all sorts of adverse effects including increased rates of obesity and higher risk of hypertension, diabetes and high cholesterol.”

One interesting thing with many habitual short sleepers is that while they're getting less sleep, the sleep they are getting is often better quality.

"They are very efficient sleepers - they get all the REM sleep and deep sleep they need and not much intermediate sleep. They're very efficient," says Professor Bruck.

However, she warns it's dangerous for people who can cope well with less sleep (which science suggests could be to do with this genetic mutation) to recommend it to others.

"It's dangerous for people to advocate it for other people because we should all adopt a sleep wake routine which makes us optimal during the day," she says.

And there's no point trying.

"In the short term you can adopt a different sleep routine but in the long term the body has the tendency to go back to what it's programmed," she says.

For those who are going through periods of partial sleep deprivation, whether as a result of work, babies or other, the good news is that you can bounce back.

"You can have a recovery sleep and you'll be amazed at how quickly the body can recover from weeks of inadequate sleep in just a few nights," she says.

However, you can't 'store' up extra sleep in preparation for these busy periods.

"It doesn't work like that unfortunately."

Dammit.