A chronobiological evaluation of the risks of canceling daylight saving time.

The long-term impact of seasonal regulation of clocks (Daylight Saving Time) is analyzed showing that it helped to mitigate the advance of the phase of human activity during the twentieth century and the exposure to the hours of the dawn in winter. The increased risks induced by circadian misalignment around transition dates are balanced by a better alignment of social clocks to the natural day in summer and in winter.