With Daylight Saving Over, Americans' Bodies Can Reset

Wynne Parry

Date: 05 November 2010 Time: 07:15 AM ET

On Sunday, at 2 a.m., most Americans will get an extra hour of sleep, thanks to the end of daylight saving time. This annual rite of "falling back" is the year's second — and less disruptive — transition associated with daylight saving time.

A person's individual, internal clock affects how one responds to the shift, but, for nearly everyone, daylight saving time is disruptive, according to Till Roenneberg, head of the Centre for Chronobiology at Ludwig-Maximlians-University in Munich. The disruption is most pronounced for the "owls" among us, who naturally sleep later than their earlier-rising counterparts, the "larks."

To keep people from snoozing at their desks or doing a mediocre job due to sleep deprivation, Roenneberg suggests work times should be flexible so that employees work eight-hour stretches that match their internal clocks' active hours.

Surveying sleep

Using data from a survey of 55,000 people in central Europe, Roenneberg and colleagues found that, overall, people slept about 20 fewer minutes per night during the summer when daylight saving time was in effect. While 20 minutes at a time may not sound like much, it adds onto an accumulated sleep deprivation, he said.

"Think of the very trivial fact that you have just mentioned — you said on a work day you cannot go without an alarm clock," he told a LiveScience writer who depends on her alarm. "If you have to wake up with an alarm clock you haven't finished your sleep. You are sleep deprived."

In fact, about 75 percent of the population whose sleep data is contained in Roenneberg's central European database relies on an alarm clock. So, before those alarms jump ahead an hour, these individuals are already sleep deprived, according to Roenneberg. The accumulated sleep debt is much worse for owls than larks.

Naturally, humans' internal time is synched to dawn. This internal tracking mechanism is demonstrated by midsleep – the time point in the middle of a night's sleep. During standard time, the average time at which midsleep occurs becomes earlier or later depending on when dawn occurs.

However, during daylight saving time, that relationship disappears, and midsleep stops tracking dawn and occurs earlier, at a constant time around 3:30 a.m., according to the research, which was published in the journal Current Biology in 2007.

In addition, the researchers followed 50 individuals' sleeping and wakefulness patterns for eight weeks around the shifts to and from daylight saving time in spring and fall. (In the spring, clocks jump ahead an hour to take advantage of summer daylight.) The results indicated that most people's circadian clocks never fully adjust to daylight saving time.

Since their internal clocks never fully set to DST, in fall, larks and owls adjust well, with the owls adjusting slightly more readily to the hour delay. A more pronounced gap between owls and larks emerged in spring. For instance, larks shifted the time when their physical activity peaks during the day forward by 40 minutes, but owls never made an adjustment over the four week period following the time change.

In the world of artificial light, people have to contend with both social time – like daylight saving – versus sun time. But in the end, sunlight holds a much more powerful sway over our circadian rhythms, according to Roenneberg.

In fact, in another study, Roenneberg and colleagues showed that the average timing of sleep was delayed by four minutes for every degree of longitude within a time zone. For instance, someone living two degrees longitude to the west of a city would experience a delay that's eight minutes more than those living in the city. This is exactly the degree of delay in sunrise as it proceeds west, he said.

Resetting the clock

The solution, according to Roenneberg, goes beyond abolishing daylight saving time.

"What we have to do is, we have to get rid of a very schizophrenic situation," he said.

On one hand, modern society has held onto the agricultural ethic, which associates rising early with productivity and industriousness. At the same time, our desire for a global economy and a global society means we expect a 24-hour work day.

Instead, the window for the work day should be expanded, and most people should be allowed to work for eight-hour stretches around their peak times within that window. Letting people work according to their own internal timing would bring many benefits, he said.

"If we dedicate our best time to our employers we would increase productive performance we would increase the quality of our free time. We would encourage a decrease in health costs," Roenneberg said. "So it is a triple win for individuals, for the economy and for the society."