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Daylight saving hits late risers hardest


We use daylight to set our body clock, but daylight savings throws this adjustment out, say researchers (Image: iStockphoto)

It may seem obvious, but science has just confirmed that daylight saving time disrupts our body clock, especially if we're late risers.

Dr Till Roenneberg of Ludwig-Maximilians University in Munich, Germany and colleagues report their findings in the journal Current Biology.

"Our data indicate that the human circadian system does not adjust to [daylight saving time]," the researchers say.

A quarter of the world's population is subjected to a 1 hour time change twice a year, yet the impact of this change is poorly understood by science.

Circadian clocks use daylight to synchronise the body to the environment and regulate sleep.

Roennenberg and team set out to study the impact of daylight saving time on the sleep patterns of 55,000 people in Central Europe.

They found that during standard time, people tended to adjust their wake up time to fit in with the dawn, but this adjustment did not happen during daylight saving time.

Larks and owls

In a separate study, Roenneberg and team looked at 50 people whose natural inclination was to wake up early (larks) or late (owls).

The researchers found that both larks and owls adjusted well to the release from daylight saving time in autumn but had problems adjusting to the imposition of daylight saving time in spring.

This was particularly the case for the late rising owls.

Roennenberg and team say the effects held for weeks, perhaps causing people to feel continually sleep-deprived in the spring and summer.

First evidence of its kind

Australian body clock researcher, Dr Greg Roach of the University of South Australia's Centre for Sleep Research, says the study is commendable, even if he does confirm what many of us already know.

"It's the best study I've seen linking sleep patterns with daylight saving time," he says.

"Until now most of the impact of daylight saving time has been anecdotal," says Roach. "One of science's aims is to find evidence for things that seem common sense."

Roach says the human body clock tends to run a bit longer than 24 hours, which means that people would naturally wake up a bit later every day, if removed from the influence of changing day lengths.

This explains why late risers would find it harder to adjust when the clock moves forward, robbing them of an hour of sleep, he says.

But Roach thinks the survey findings that show people adjust their wake up time to fit in with the changing time of dawn would not generally apply to people who live in cities.

"In cities, the time that determines what time you get up is what time you need to get the kids to school or what time you need to be at work," he says.

Most states in Australia will commence daylight saving on Sunday 28 October.

Tags: environment, health, agricultural-crops, biology