"Before artificial lighting, humans tended to live much more by the sun cycle," Ptacek said. "Whereas, now, people stay up all night and turn the lights on, which affects our biological clock. There is no question that we have been changing our clocks long before daylight saving time came along."
So, it's not surprising that daylight saving time affects our internal clock, Ptacek said. However, it is no more unnatural than our use of artificial light, he noted.
There is no reason to abandon daylight saving time, Ptacek added. "There may be societal benefits to daylight saving time, such as saving energy," he said. In any case, it is no more disruptive than the other things we do to manipulate time, he said.
Another expert believes daylight saving time isn't really useful, however.
"I don't think it is valuable to change to daylight saving time," said Ralph Downey III, the chief of sleep medicine at Loma Linda University Medical Center in California. "Five o'clock to the body clock is five o'clock," he said. "But, socially, things change, and that's also a time-giver."
For more on the body's clock, visit the U.S. National Institute of Mental Health.
SOURCES: Till Roenneberg, Ph.D., Ludwig-Maximilians-University, Munich, Germany; Louis Ptacek, M.D.,investigator, Howard Hughes Medical Institute, John C. Coleman Distinguished Professorship in Neurodegenerative Diseases, professor, Department of Neurology, University of California, San Francisco; Ralph Downey III, Ph.D., chief, Sleep Medicine, Loma Linda University Medical Center, Loma Linda University Children's Hospital, Calif.; Oct. 24, 2007, online edition, Current Biology