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Stanford University School of Medicine

Stanford expert weighs in on daylight saving time and that extra hour of sleep

Every year on a Sunday in fall our clocks are adjusted backward by one hour, granting people in North America, Europe and parts of the Middle East a seemingly airtight excuse to sleep in. If you live in one of the estimated 70 countries that participates in daylight saving time (DST), you're probably familiar with its pros and cons and you're faced with a dilemma that could affect your health: Do you use your extra hour to sleep, or would you feel and function better if you stick to your sleep schedule as if DST never happened at all?

To answer that question and learn more about the benefits of DST – which was first proposed in 1895 by a scientist named George Hudson – I reached out to sleep expert Clete Kushida, MD, PhD, medical director of the Stanford Sleep Medicine Center.

According to Kushida, there are no clear studies on how DST directly affects our physical and mental health. Although some research suggests DST has negative effects, such as the study by scientists at Stanford and Johns Hopkins that found a small, but significant increase in fatal car accidents on the Monday after DST in the spring, other research yielded findings that are tricky to interpret. For example, a study found a 25 percent increase in the number of heart attacks the Monday after we “spring forward," and a 21 percent decline in the number of heart attacks on Tuesday after DST in the fall. Yet, the total number of heart attacks the week after DST didn't change.

I asked Kushida for additional insights on DST and how he manages his sleep schedule. Here's what he had to say:

Are the effects of daylight saving time nontrivial?

It's highly dependent on the individual; for some who have a strong internal clock with very constant bedtimes and awakening times, even a one-hour time change can cause them to have sleep issues for weeks. That said, most individuals have an internal clock that is longer than 24 hours, which means that they have a natural tendency to want to sleep later and get up later, so most people don't have difficulty adjusting to DST.

Are some people (such as those with sleep or mood issues) negatively affected by daylight saving time more than others?

Any individuals who have sleep difficulties caused by medical or sleep disorders may have problems; however, with DST, they usually don’t have issues.

How do you manage your sleep schedule with the extra hour afforded to you by daylight saving time?

I still try to keep my same schedule, but DST helps because you become sleepier a bit earlier.

With the daylight saving time shift, it’s temping to take advantage of the hour and sleep in for a day. Is this indulgence okay, or is it too abrupt of a shift for our bodies?

It's always better to keep consistent bedtime/awakening times.

Photo by Lars Plougmann

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