Body's Clock Never Adjusts to Daylight Savings Time

By Steven Reinberg
HealthDay Reporter
Wednesday, October 24, 2007; 6:00 PM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

WEDNESDAY, Oct. 24 (HealthDay News) -- Changing to daylight savings time may give people an hour more of sunlight, but it appears that their internal body clocks never really adjusts to the change, German researchers report.

In fact, daylight savings time can cause a significant seasonal disruption that might have other effects on our bodies, according to the report in the Oct. 24 online edition of Current Biology.

"When you change clocks to daylight savings time, you don't change anything related to sun time," explained lead researcher Till Roenneberg of Ludwig-Maximilians-University in Munich. "This is one of those human arrogances -- that we can do whatever we want as long as we are disciplined. We forget that there is a biological clock that is as old as living organisms, a clock that cannot be fooled. The pure social change of time cannot fool the clock."

People's circadian rhythm -- the body's internal clock -- follows the sun and changes depending on where you live. It actually changes in four-minute intervals, exactly the time it takes for the sun to cross one line of longitude, Roenneberg explained.

"The circadian clock does not change to the social change," Roenneberg said. "During the winter, there is a beautiful tracking of dawn in human sleep behavior, which is completely and immediately interrupted when daylight savings time is introduced in March," he said. It returns to normal this year when standard time returns on Nov. 4, he added.

Daylight savings time may be one cause of what Roenneberg called our lack of seasonality. By seasonality, he means that our internal clock is in tune with the natural change in light throughout the year. "This could have long-term effects," he said.

In the study, Roenneberg's group collected data on the sleep patterns of 55,000 people in Central Europe. The researchers found that sleep time on days off work when daylight savings time took effect followed the seasonal progression of dawn under standard time, but not under daylight savings time.