German researchers say that daylight savings time can cause a significant seasonal disruption that might have other effects on our bodies, according to a report in the online edition of Current Biology.
Apparently your circadian rhythm – what you might call 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, according to lead researcher Till Roenneberg of Ludwig-Maximilians-University in Munich.
“When you change clocks to daylight savings time, you don’t change anything related to sun time,” explained Roenneberg, according to a HealthDay News report. “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.”
“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 – and doesn’t return to normal until standard time is reintroduced (this weekend for most in the US).
Worse – daylight savings time may be one cause of what Roenneberg referred to as a 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. In a another study, Roenneberg’s group looked at the timing of sleep and activity for eight weeks during the change to daylight savings time in 50 people, taking into account each person’s natural clock preferences, or “chronotypes,” which range from morning larks to night owls. For both morning larks and night owls, their timing for sleep and peak activity easily adjusted when daylight savings time ended in the fall – but it never adjusted to the return to daylight savings time in spring. This was especially true for those who stay up late and sleep late.
“If we didn’t change to daylight savings time, people would adjust to dawn during the summer and again to dawn in the autumn,” Roenneberg. “But this natural adjustment is interrupted by daylight savings time,” he said.
An Early Start?
To make matters worse – the Energy Policy Act of 2005 extended Daylight Saving Time in the U.S. – springing us ahead two hours earlier in the spring – and delaying the return to standard time by a week (this weekend). Aside from us mere mortals, you may already have found that some devices (VCRs, DVDs, even car clocks and blackberries) didn’t get the “message’ – and made the switch a weekend “early.’