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Tweaking sleeping habits can shift people's body clocks and improve their wellbeing, say scientists in the UK and Australia.

They focused on "night owls", whose bodies drive them to stay up late into the night.

Techniques used included consistent bedtimes, avoiding caffeine and getting plenty of morning sunshine.

The researchers say their approach may seem obvious, but could make an important difference to people's lives.

Everyone has a body clock whose rhythms follow the rising and the setting of the sun. It is why we sleep at night.

But some people's clocks run later than others.

Morning-led "larks" tend to wake early, but struggle to stay up in the evening; night owls are the opposite, preferring a lie-in and remaining active late into the night.

The problem for many night owls is fitting into a nine-to-five world, with the morning alarm waking you up hours before your body is ready.

Being a night owl has been linked to worse health.

Image caption Are you a lark or an owl?

Scientists studied 21 "extreme night owls" who were going to bed, on average, at 02:30 and not waking until after 10:00.

Their instructions were to:

Wake up 2-3 hours earlier than usual and get plenty of outdoor light in the morning

Eat breakfast as soon as possible

Exercise only in the morning

Have lunch at the same time every day and eat nothing after 19:00

Banish caffeine after 15:00

Have no naps after 16:00

Go to bed 2-3 hours earlier than usual and limit light in the evenings

Maintain the same sleep and wake times every day

After three weeks, people had successfully shifted their body clocks two hours earlier in the day, the analysis by the University of Birmingham, University of Surrey and Monash University showed.

The results, in the journal Sleep Medicine, showed people still got the same hours of shut-eye.

But they reported lower levels of sleepiness, stress and depression, while tests showed their reaction times also improved.

"Establishing simple routines could help night owls adjust their body clocks and improve their overall physical and mental health," said Prof Debra Skene from the University of Surrey.

"Insufficient levels of sleep and circadian [body clock] misalignment can disrupt many bodily processes, putting us at increased risk of cardiovascular disease, cancer and diabetes."

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One of the main cues the body uses for syncing with the passage of the sun is light - hence advice to expose the body to more during the day and less at night.

Having inconsistent sleeping and waking times can also disrupt the body's internal clock (known as a circadian rhythm).

The techniques deployed may seem like obvious sleep hygiene advice, but each is used to help train the body clock.

What the researchers did not know was whether those hard-wired to sleep late would respond to the change of habits.

"What isn't obvious is, when you have these extreme night owls, can you do anything about that?" Dr Andrew Bagshaw, from the University of Birmingham, told the BBC.

"These are relatively simple things anyone can do that makes an impact, and that to me is surprising.

"Being able to take a decent chunk of the population and help them feel better without a particularly onerous intervention is quite important."

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