The pros and cons of daylight saving time

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Would you like an extra hour of sleep?

What if it meant losing an hour 6 months later?

For many people around the world, this question isn’t hypothetical; it’s standard practice.

People in countries that participate in daylight saving time (DST) typically set their clocks forward an hour during the spring and summer, then reset them to the global standard in the fall and winter to get the most out of natural daylight hours.

What are the benefits of this practice—and do they outweigh the consequences of interfering with the body’s natural rhythms twice a year?

There are indeed some health benefits to “springing forward.” Longer evening daylight tends to encourage better physical health. A study found that children living in countries that practice DST were more physically active in the late afternoon and early evening during the spring and summer[1].

Despite these benefits and the good intentions behind DST, it’s a source of frequent complaints in countries that follow it. About half the countries that once used DST have since abolished it, and fewer than 40 percent of the world’s countries still use it today[2].

It turns out there are some legitimate reasons for complaint. That hour of sleep you lose at the beginning of DST may wreak more havoc than you think.

For instance, on the Monday immediately following the switch to DST, workers sustain more, and severer, workplace injuries compared with the rest of the year[3]. Because of the time shift, they sleep about 40 minutes less Sunday night; on Monday, they have about 6 percent more injuries, and lose about 68 percent more work days because of these injuries.

Interestingly, when workers switch back to standard time in the fall, they tend not to get any more sleep than usual, and we see no decrease in injuries from being well-rested.

Likewise, switching clocks forward for DST also increases the number of cardiac arrests by 25 percent for that Monday[4]. This effect trails off over the rest of the week, as people adjust to their new sleep schedules. Keep in mind that even with a 25 percent increase in cardiac arrests, your chances of experiencing one on that Monday are still exceedingly low!

Perhaps most surprisingly, losing an hour of sleep has been shown to compromise the moral judgments of experienced professionals. When judges show up to court groggy on the Monday after the switch to DST, they give significantly harsher sentences—about 5 percent longer compared to other Mondays[5].

Whether you’re for or against DST, you are pretty much stuck with whatever decision your country has made around it.

If you live in a country that uses DST, try to make the most out of your extended sunlight hours by spending time outdoors during your spring and summer evenings.

But, more importantly, allow yourself some extra time to adjust to your new sleep schedule when you change the clocks forward in the spring. You can prep for DST by getting exposure to sunlight early in the morning, which will help you fall asleep earlier at night. Your body and the people around you will thank you for it!

?References

1. Goodman, A., Page, A.S., & Cooper, A.R. (2014). Daylight saving time as a potential public health intervention: An observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries. The International Journal of Behavioral Nutrition and Physical Activity, 11, 84.
2. Time and Date AS. (2017). Daylight Saving Time Statistics. Retrieved from http://www.timeanddate.com.
3. Barnes, C.M., & Wagner, D.T. (2009). Changing to daylight saving time cuts into sleep and increases workplace injuries. Journal of Applied Psychology, 94, 1305-1317.
4. Sandhu, A., Seth, M., & Gurm, H.S. (2014). Daylight savings time and myocardial infarction. Open Heart, 1, e000019.
5. Cho, K., Barnes, C.M., & Guanara, C.L. (2017). Sleepy punishers are harsh punishers: Daylight saving time and legal sentences. Psychological Science, 28, 242-247.