Should We Let Go of Daylight Saving Time?

Every year around March, as the days get longer and spring arrives in the northern hemisphere, many clocks around the world spring one hour forward to daylight saving time (DST). What used to be 2 pm will now become 3 pm, and our schedule is shifted one hour earlier to use more daylight.

Doesn’t sound too bad, does it? Since everything starts earlier, we get more light later in the evening after the workday is done, almost like flying to a neighboring country that is one time zone to the east (for instance, from Los Angeles to Denver) and then getting used to the local clock.

But there is a very important difference between DST and typical jet lag, and this difference is one reason the scientific community has been calling to abolish DST for several years now. Let’s dig deeper into this thing called DST and understand why it’s bad for us and what we should do instead. (Spoiler alert: We should not make it permanent!)

What is DST?

The idea to artificially shift the clock in the springtime originated in 1907 as a way to save energy by being active earlier and thus "using" more natural light during spring and summer. Many countries adopted DST following the second world war, and currently, approximately 1.6 billion people experience it yearly.

Since DST is mostly about trying to save sunlight, countries or states that are close to the equator (like Hawaii, for instance) realized early on that changing the clock is not for them. In these places, the sun shines for a similar amount of time across the year, so DST was quickly rejected in favor of a permanent clock year-round.

There are two main reasons we should all follow Hawaii’s example and abandon DST. The first concerns sleep, and the second our biological clock.

DST Triggers Sleep Loss

Because the switch to DST typically happens at night, studies show that people lose between 40-60 minutes of sleep during the DST transition. This finding makes sense when you take into account that people typically go to sleep still in Standard Time (say 11 pm), but when they wake up at their usual time, they are already an hour late since DST "stole" an hour from their sleep at night.

Losing an hour of sleep may not sound like much, but studies have found a dramatic impact of this annual sleep loss on human health and safety. After the switch to DST, there is a 24 percent increase in cardiovascular events, an 8 percent increase in strokes, and a 6 percent increase in fatal car accidents across the U.S. Additional victims of what is known as sleepy Monday (the first workday after the DST transition) include increased workplace accidents, harsher court verdicts, and reduced donations to charity.

The accumulation of these negative outcomes has sparked many debates calling to end the annual clock shift and adopt a permanent clock year-round. But which clock to keep? DST, the one we use in the summer and spring months, or Standard Time, the one that dominates the winter and autumn? This question brings us to the second consequence of DST – the disruption to our biological clock.

DST and the Biological Clock

The impact of DST on sleep is typically short-lived and can reset after a week or two, but DST’s longer, less conspicuous impact on human physiology doesn’t go away so quickly. To try and understand this aspect, let’s imagine adding another watch to our right hand. So on the left hand, we have our typical clock (what I’ll term the social clock) — the one that tells us when to go to work or when to meet friends. This clock will spring one hour forward when DST starts and move back one hour when it ends.

Now to the new clock on our right hand. This clock will tell time-based on the sun (the sun clock)- it will show noon when the sun is at its highest point in the sky and midnight about 12 hours later when the sun is nowhere to be seen (in most latitudes anyway).

The east-west trajectory of the sun across the sky, with noon signifying its highest point.

Source: Formative

During Standard Time, our two clocks show roughly the same time – noon is the time the sun is at its highest point in the sky. However, during DST, there will be a mismatch between our two clocks. If we glance at our regular social clock at noon, the sun clock on our right hand will say it is only 11 am. This hour difference between our clocks will not go away until DST is over many months from now in the fall. Why is that important? Can’t we just ignore the sun clock and carry on with our lives? Clearly, we can, but it comes at a price that more and more scientists are worried about.

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One issue has to do with our biological clock. Unlike the other two clocks, this clock is internal, situated deep in the brain. Decades of research tell us that the biological clock sets its time based on the sun. In other words, it follows the clock on our right hand. The biological clock decides when it is time to sleep and when to wake up by tracking the strength and color of sunlight across the sky (bluer in the dawn, redder at dusk).

It has done so for millions of years and continues to track the sun even when humans created their own social clock or invented indoor lighting. So, if there is a mismatch between the social clock on our left hand and the sun clock on the right – the brain and body will still closely match the sun clock on the right.

For example, let’s say I like to go to sleep at midnight. During DST, my sun clock will show midnight when my social clock shows 1 am. Since the body is mostly tuned to the sun clock, I might find that I am not tired enough to fall asleep when my social clock says midnight since it is only 11 pm on my sun clock! DST keeps our biological clock one hour early relative to the social clock disrupting our physiological schedule.

This is exactly what researchers found when they examined individuals’ cortisol responses across 3 years. Cortisol is typically released when we wake up and is thought to provide an energy boost at the start of the day. The study found that peak cortisol was released an hour later during DST relative to non-DST months. In other words, the physiological systems in our bodies kept releasing cortisol based on the clock on our right hand, the sun clock, ignoring the new social clock (that is now an hour later). This is a key point to emphasize. Unlike jet lag, when our biological clock eventually synchronizes to the new time zone, our biological clock does not fully adjust when we shift to DST. It stays one-hour jet-lagged for as long as DST persists.

From these findings, you can appreciate why it would make sense to abolish DST and keep following the social clock that most resembles the sun: Standard Time. Once we do that, our three clocks, the one in our brain and the two on our hands will point to roughly the same time across the year. If we keep DST permanent, the artificial jet lag between our social clock and the sun clock will never go away. This could have serious negative effects on human health that are still unknown.

Shift workers who chronically suffer from a mismatch between their biological clock and their social schedules (for instance, having to work in the middle of the night) are at a greater risk of suffering from diabetes, cancer, and heart disease. We still do not know if DST has a similar impact as shift work, but one thing they both have in common is a disruption of the biological clock.

In the U.S., DST currently has the upper hand. On March 2022, the Senate passed the Sunshine Protection Act, an act that will make DST permanent, increasing daylight in the evening and potentially boosting economic activity after work.

Trying to maximize daylight is like using a blanket that is a bit too short. A part of you will always stay cold. If we choose to get daylight in the evening, we get children waiting for their school bus in complete darkness. If we want more sunlight in the mornings, we get to drive back home in the dark. Since both options are not favorable, the discussion over the permanent clock should weigh in the chronic disruption to our biological clock, an issue that is unique to DST.

If I can offer one sentence to sum up all our clock dilemmas, it would be this: We should lose DST to protect our sleep and keep Standard Time to protect our biological clocks.

Happy winter, everyone!