A study from Current Biology noted that although around one-quarter of the world's population participates in DST, little research has been done on the effect of DST on human circadian clocks, which are influenced by light exposure and play an important role in helping people to synchronize to their environment. In the second part of this two-part study, researchers looked at 50 subjects who were "chronotyped," or classified as either "night owls" or "early birds" to see how they were effected by the time change before and after the start of DST. Specifically, the scientists wanted to assess the ability of the individual to adjust to the time change.
What the study showed is that while both chronotypes adjust fairly easily to the end of DST which takes places in the autumn, that the time adjustment in the spring is more difficult. This is especially true for "night owl" chronotypes: while the "early birds" adjusted more readily to the change, the adjustment of late chronotypes was never complete.
These findings are echoed in a second study, published in Sleep Medicine, which looked specifically at the effects of daylight savings time on a group of adolescents. It showed that older students and "night owl" students both suffered from higher rates of daytime sleepiness for several weeks after the time change.
In short, although DST is a now a tradition — not only in the United States but around the world — the fact remains that this annual shift, particularly in the spring, can cause disturbances in sleep. This occurs particularly for late chronotypes, "night owls," whose circadian clocks are set to a later bed time and tend to not as easily change their sleep/wake patterns.