Researchers have been trying to catalog the effects of daylight saving time for years, with conflicting results.
A 1996 study in the New England Journal of Medicine claimed an 8 percent jump in traffic accidents on the Monday after the switch, but a follow-up report two years later suggested that figure was lower. In 2000, a group of Swedish researchers concluded that the change did not have any significant effects on the number of crashes in that country. Jump forward to 2009, though, and Michigan State University psychologists Christopher Barnes and David Wagner report that there are more workplace injuries on the Mondays following that lost hour.
Elise Amendola, AP
Adjusting clocks forward an hour this Sunday for daylight savings may throw off our natural rhythms. Here, a worker at Electric Time Co. in Medfield, Mass. cleans his company's massive clock faces in 2008.
The potential danger of daylight saving time aside, it is clear that the changes throws off our natural time-keeping rhythms. Till Roenneberg, a chronobiologist (this is no misprint) at the University of Munich, says that our internal clocks set themselves according to the environment. So, our natural chronometers keep time with the sun, not the alarm clocks sitting by our beds, and this is the main reason it is hard for us to adjust.
In one study, he found that people within a given time zone tend to rise in tune with the sun's crossing. "They get up four minutes later for each longitude you go west," he says. "The internal clock seems to be looking to the sun rather than listening to the alarm."
Daylight saving time throws this system out of balance. When we move back our clocks, Roenneberg says: "The social times change but the sun time does not." In 2007, his group described the results of a project that involved monitoring subjects four weeks before the change, and four weeks afterward. "If you look at sleep, it looks as if people have a hard time adjusting -- they tend to lag later on in the day for at least a month following the change," he says. But he also studied the activity profiles of the individuals and found that late sleepers in particular have a hard time adjusting. They lag later on in the day.
"Everybody says, 'Oh, come on, it's only an hour,'" Roenneberg says. "But an hour in the relationship of our behavior towards dawn may mean a change back three weeks in the seasonal progression. The impact may be greater because of these seasonal effects than we ever thought."
Roenneberg says there is still plenty of research to be done on the subject, but his work thus far suggests that showing up late for work this Monday and blaming daylight saving time would not be a scientifically valid excuse. That afternoon coffee break, however, is an entirely different matter. From a chronobiological perspective, you might need it more than ever.
