Why we should let the sun set on Daylight Saving Time

The American Academy of Sleep Medicine recently published a position statement, aligned with the European Sleep Research Society, European Biological Rhythms Society, and Society for Research on Biological Rhythms’ position, calling for the abolishment of daylight saving time (DST) in favor of the maintenance of standard time year-round. While many people feel that ending the twice-yearly clock shift is the right thing to do, few people realize that choosing to keep the clocks permanently on DST over standard time could impact their short-term well-being and long-term health. 

Daylight Saving Time can make you stay up too late

Put bluntly, living on DST is like staying up later than you should, but for 6 months straight. Let’s first consider the impact of staying up late for one night, perhaps having watched one too many episodes of your latest Netflix binge. The next morning you probably struggled to wake up to your alarm for work or school and told yourself that you’d go to bed early the next night in order to catch up. After feeling a little sluggish during the day, you get home and begin your evening routine, only to feel a second wind of energy when you had planned to go to bed. Feeling this boost of energy, you might find yourself staying up late again. This cycle of late bedtimes, short sleep, and morning grogginess is a pattern that many conscientious people unintentionally sink into, but why does it happen? And what does it have to do with DST?

Our body uses light to reset our clocks

To answer this we need to understand how our body clock works. We each have an internal clock, or circadian rhythm, which works to align your body rhythms with the 24-hour cycle of sunlight and darkness that we experience living on Earth. The light that you are exposed to each day travels through your eyes and signals your brain to set your clock to help you stay awake during the day and sleep at night. It’s the timing of these light signals that is most critical for keeping everything running, well, like clockwork. When you are exposed to the bright light of a sunrise in the morning, it helps your circadian rhythm wake you up. When you are exposed to bright light in the evening, however, it signals your body to stay awake, leading to later sleep and wake times. 

Our social clocks impact our body clocks

The way that we are exposed to sunlight each day is largely driven by our social schedules for work, school, and interactions with others. Our social schedules, in turn, are largely set by the time on the clock. When we set our clocks to standard time, most individuals experience sunrise and sunset earlier in the day relative to the clock. This means bright morning light, and darker evenings. In contrast, when we set our clocks for DST, we experience sunlight at a later time relative to the clock. Practically speaking, this means that the cycle of feeling alert before bed, having a short sleep, then feeling tired in the morning is more likely to happen when we are living on DST because the evening light exposure that we experience can cause a delay in sleep times, while our morning alarm time stays the same. 

Later sunlight is linked to poorer health

Living with your internal clock slightly offset from the solar light-dark cycle has been termed ‘social jet lag,’ and it has significant consequences, including short sleep duration, increased metabolic disorders, cardiovascular problems, and mood disorders, and even reduced life expectancy. People living on the western edges of time zones provide a stark example of how a small difference in the relationship between the timing of sunrise-sunset and clock time can affect population health. Individuals who live on the westward side of a time zone, where there is more sunlight in the evening, have a higher risk of poor health and shorter life expectancy compared to those who live on the eastern edge of a time zone, where the sun rises and sets earlier relative to the clock time. 

While it may not be possible to ensure that everyone goes to bed on time every night, we can minimize the disruption to our body clocks that causes people to unintentionally stay up too late, and the negative consequences that come with it, by abolishing DST in favor of standard time.

About the authors: Erin Flynn-Evans, PhD MPH, is the director of the Fatigue Countermeasures Laboratory at NASA Ames Research Center whose work focuses on improving sleep, performance, and safety in air and space travel. Cassie Hilditch, PhD, is a senior research associate in the same lab and is currently investigating countermeasures to sleep inertia.