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Daylight savings time disrupts humans’ natural circadian rhythm

Public release date: 24-Oct-2007

When people living in many parts of the world move their clocks forward one hour in the spring in observance of daylight saving time (DST), their bodies’ internal, daily rhythms don’t adjust with them, reports a new study appearing online on October 25th in Current Biology, a publication of Cell Press. The finding suggests that this regular time change—practiced by a quarter of the human population—represents a significant seasonal disruption, raising the possibility that DST may have unintended effects on other aspects of human physiology, according to the researchers

“When we implement small changes into a biological system which by themselves seem trivial, their effects, when viewed in a broader context, may have a much larger impact than we had thought,” said Till Roenneberg of Ludwig-Maximilian-University in Munich, Germany. “It is much too early to say whether DST has a serious long-term impact on health, but our results indicate that we should consider this seriously and do a lot more research on the phenomenon.”

“While we generally think that the time changes enforced by the DST transitions are ‘only an hour,’ they have far more drastic effects if viewed in the context of the circadian clock’s seasonal changes,” Roenneberg said. “This seemingly small hour translates to a repeat of 10 weeks in the annual progression of the relationship between our sleep-wake cycle and dawn—four weeks in spring and six weeks in autumn. In effect, it’s as if the entire population of Germany, for example, is transported to Morocco in spring and back again in autumn.”

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