- - Does Daylight Saving Time Have Long-Term Effects on Health?

Does Daylight Saving Time Have Long-Term Effects on Health?

The annual transition to and from daylight saving time (DST) has clinical implications that last longer than the days when clocks “fall back” or “spring forward.”

Over time, DST eliminates bright morning light that critically synchronizes biological clocks, which can be associated with an increased risk of heart attack and ischemic stroke, as well as other negative effects of partial sleep deprivation.

Average sleep duration shrinks by 15 to 20 minutes for adults during DST transitions, which may also increase the risk of fatal accidents.

“People think the one-hour transition is no big deal, that they can get over this in a day, but what they don’t realize is their biological clock is out of sync,” said Beth Ann Malow, MD, Burry Chair in Cognitive Childhood Development, and professor of Neurology and Pediatrics in the Sleep Disorders Division at Vanderbilt University Medical Center.

“It’s not one hour twice a year. It’s a misalignment of our biological clocks for eight months of the year. When we talk about DST and its relationship to light, we are talking about profound impacts on the biological clock, which is a structure rooted in the brain. It impacts brain functions such as energy levels and alertness,” she said.

Malow and colleagues published a JAMA Neurology commentary today recapping large epidemiological studies that advocate for ending the practice of setting clocks forward or back.

Some people may have more flexible circadian rhythms and adjust quickly while others are more sensitive. Malow, an expert on autism and sleep, said that the transition impacts some children with autism for weeks or months.

While the sleep and circadian communities believe returning to standard time may be more biologically appropriate, gaining political buy-in for a nationwide change remains a challenge. State legislation is “all over the map,” with some states considering a return to standard time and others in favor of permanent DST. Tennessee has passed legislation supporting permanent DST, although such a change would require action from the U.S. Congress.

When did Daylight Saving Time Begin? 

It all started with Benjamin Franklin in 1784. During his time as the ambassador to France, Franklin wrote a lighthearted letter to The Journal of Paris, wherein he satirically complained of being woken up too early by the bright morning sun. In the essay he suggests Parisians change their sleep schedules to wake up at dawn, enabling them to save “by the economy of using sunshine instead of candles.”

However, Franklins was meant to be humorous and merely suggested changing the Parisian’s sleep schedule – not switching clocks forward.

Over a century later, in 1907, an English builder and horseman William Willett published a pamphlet advocating moving the clocks forward 20 minutes a week for 4 weeks in April. He wanted to grant people like himself more opportunities for daytime recreation and cost savings in electrical lighting. Even though he had champions like Winston Churchill by his side, Willett died in 1915 and never saw Parliament pass his idea.

It took the hardships of war for DST to finally pass. During World War I, countries needed coal to support the war efforts, but rations were running slim. In 1916, Germany became the first country to implement DST, with others like Britain following suit soon after.

Despite the common myth, farmers had nothing to do with the founding of DST. In fact, they heavily opposed it, leading to its repeal in 1919 after the war was over. DST is actually very disruptive to farmers since their schedules already follow the sun. With DST in place, their workday was delayed by an hour, as they had to wait longer for morning dew to evaporate from their hay. It was cut short on the other end, too, since employees continued to leave at the same time for dinner.

Since the 1919 repeal of national DST in the U.S., the time change has been regulated at a state and local level. Any changes to the practice are usually dictated by commercial interests (not farming ones).

Interesting Facts about Daylight Saving Time

Daylight Saving Time certainly has an interesting history, but the fun facts don’t stop there. Here are a few more trivia-worthy tidbits about this practice.

It’s reversed the birth order of twins

In November 2016, right after “Fall Back,” a pair of twin boys were born on either side of the time change. One boy was born at 1:39 am and the other at 2:10 am, or rather, 1:10 am. The second twin was younger by 31 minutes, but since his date of birth was recorded after the time change, his birth certificate says he’s 29 minutes older!

Halloween used to be much darker

The end of Daylight Saving Time didn’t always take place in November in the U.S. It used to take place earlier, making Halloween a suddenly very dark night—which made parents nervous about their children’s safety, and candy makers very nervous about their sales.

In the 1980s, the National Confectors Association lobbied, along with golf and barbeque industries, to push the end of DST back a week into November. Their dreams weren’t answered until 2007 when President George W. Bush extended daylight saving time as part of the Energy Policy Act.

It makes bartending interesting

In many large cities, it’s common for bars to stay open until 2 am. In the fall, this coincides with Fall Back. While the bar can decide whether or not they want to close at the “normal” time or not, many decide to stay open, effectively giving partygoers an extra hour out on the town.

In the spring, partiers may be unhappy to hear, that means bars technically close one hour early since the clock says 2 am at 1 am. Stay open later, and the bar could risk an after-hours service violation.

Not everyone uses the 1-hour standard

The vast majority of countries participating in DST shift their time by 1 hour. But in one place in the world, time only shifts by 30 minutes. From April to October, residents of Lord Howe Island off the east coast of Australia are 30 minutes ahead of their time zone counterparts.

Who uses Daylight Saving Time?

Currently, less than 40% of countries participate in DST, a number which includes countries in both the Northern and Southern hemispheres. DST begins for Northern Hemisphere countries in the spring, between March and April, and ends in the fall, between September to November.

Because summer occurs at the opposite time of year for Southern Hemisphere countries, they practice DST between September to November and March to April. Countries around the equator do not participate in DST, since their amount of sunlight stays relatively stable throughout the year.

The number of countries participating in DST continues to fluctuate. Some countries observe DST sporadically. One such example is Libya, which used it continuously from 1982 to 1989, then again in 1997 and 2013. Chile delayed the start date of DST twice, for a 1987 Pope visit and a 1990 presidential inauguration.

Some countries have given up DST completely. A few of the major countries that no longer participate in DST include Japan, India, and China.

In fact, not even all parts of a country may participate in DST. In the U.S., Hawaii and Arizona do not observe DST, and some Canadian provinces do not observe it. Today around 70 countries use DST in at least some part of their country.

Other benefits and drawbacks of Daylight Saving Time

Some countries continue to participate in DST because they believe the extra daylight is beneficial to society, perhaps resulting in fewer traffic accidents and more opportunities for outdoor exercise. Other countries don’t believe the tradeoff is worth it, considering the disruptions DST causes to a 24-hour, global economy, and growing research indicating an increase in workplace injuries and heart attacks in the first week following the springtime change.

To date, the research suggests some clear benefits to DST, some clear disadvantages, as well as some inconclusive evidence as to whether DST has a positive, negative, or neutral effect on some things.

More daylight

One of the biggest arguments for DST is that we get more daylight in the evening. In theory, this gives us more time to spend outdoors with recreational activities like exercise, reduces the risk of car accidents since fewer people are driving when it gets dark, and lessens our reliance on indoor lighting.

Energy conservation

This last point gets to the main reasons proponents give for sticking to DST: energy conservation. DST went into place during WWI, to reduce the burden on coal production. With more daylight, the theory goes, we need fewer energy resources. A U.S. Department of Transportation study from 2008 found that the total electricity savings are about 0.5% during each day of DST, which equates to a .03% reduction averaged over the course of the year.

However, more recent studies suggest DST does the opposite; it may increase energy consumption. In 2008, Indiana researchers analyzed the effect on energy consumption during DST. In contrast to popular belief, they found that residential electricity demand actually increases during DST by 1%. While we might expect to save money on lighting since we have an extra hour of natural sunlight, in reality those costs seem to be offset by an increase in heating and air conditioning during the time people spend inside.

Add to all this the fact that today’s light bulbs are much more energy-efficient, so lighting is less of a drain on our total energy consumption than it was when DST first began.

Reduced crime

Putting the energy issue aside, there are other, unintended benefits to DST. Crime tends to occur more during the nighttime hours, and one 2015 study found that the daily robbery rate drops 7% following the beginning of DST in the spring, thanks to the sudden increase in daylight evening hours.

How were the study authors able to definitively attribute this to DST? The overall rate dropped overall by 7% but it dropped by 27% during the hour that suddenly had sunlight.

Economic impact

One issue with DST is the lack of coordination among countries worldwide, despite their participation in a global economy. As we reviewed above, countries practice DST to varying extents (or not at all) at different times during the year. This makes it difficult to communicate globally, especially in the immediate days following a time change.

One 2011 study found a “surprisingly strong” negative relationship between DST and SAT scores. Using the estimate that a 1-point reduction in SAT scores is associated with a 1.5% difference in annual earnings, the researchers extrapolated the yearly economic impact could be as high as a $1.29 billion loss for a state like Indiana.

Lack of public enthusiasm

Only 55% of people don’t mind DST. The other 45% either find it somewhat or majorly disruptive to their lives. The arbitrary time change feels disruptive, and people get bummed about leaving for work in the darkness, or heading home in the darkness when it was previously light out.

Driving accidents

A few studies have been done regarding the relationship between DST and a rise or fall in traffic accidents. Thus far, the results are conflicting.

One 2001 study attributed a “small increase” in fatal accidents the Monday following DST to the resulting sleep deprivation from Spring Forward. Meanwhile, a 2010 study found that the increase in car crashes the day following DST was “not statistically significant,” and that overall DST led to fewer crashes due to improved visibility. Yet another study from 2010 found that DST had no impact on traffic accidents, positive or negative.

Finally, DST has a negative impact on your sleep, which trickles down to other health aspects of your life. We’ll review these in the following section.

Does Daylight Saving Time affect sleep?

Even in instances where we don’t realize it, the effect DST has on our sleep is significant and negative.

DST and sleep deprivation

A 2013 study published in Sleep Medicine found that while people generally believe they adjust to the new schedule quickly, it takes them at least a week to do so. During that time, they’ll experience fragmented sleep and an overall sleep loss that results in sleep deprivation during the spring change.

Perhaps more surprisingly, these negative effects to sleep persist during the fall time change, when people popularly believe they enjoy an extra hour of sleep. The same study found that people generally do not get extra sleep on that first night. Further, they continue to wake up earlier than their clocks would have them do so over the next five days, resulting in a net loss of sleep for the week.

The study authors found that sleep deprivation in the week following both the beginning and end of DST indirectly led to higher rates of traffic accidents and a disruption to bodily functions that shouldn’t be ignored.

What will happen with Daylight Saving Time in the future?

The number of countries practicing DST continues to change. Each year bills get proposed to adjust or change DST. Sometimes they get passed, and sometimes they don’t.

Here at Tuck, we don’t take sides in the ongoing debate for and against DST, but there are definitely some interesting things happening in the world revolving around this practice.

Here’s some of the latest news and legislation happening around DST.

In the United States:

In 2018, Florida passed the Sunshine Protection Act. This act would exempt Florida from the federal 1966 Uniform Time Act and transition Florida to adopt DST year-round—meaning that for half of the year, it would be 4 hours ahead of its counterpart on the West Coast.

The Uniform Time Act gives states the option to either adopt DST or to remain on standard time all year (as Arizona does). To switch to year-round DST, this Act needs to change. While the bill was approved in the Florida state Senate and House, it still needs to be approved by Congress. Until that happens, Florida will continue to practice DST like the rest of the states.

Similarly, in California, residents voted to approve Proposition 7 on the midterm ballot by nearly 60%. Because California had adopted DST through Proposition 12 in 1949, it needed to be repealed by voters before the state legislature could take action toward changing DST in the state. Prop 7 repealed Prop 12, paving the way for California to move to year-round DST—once Congress modifies the Uniform Time Act.

Other states currently seeking exemptions from the federal Uniform Time Act include Montana, Texas, and Nebraska.

In Europe:

When the European Union surveyed 4.6 million of its residents, they found that 84% disliked seasonal time changes. Beginning at the end of October 2019 (or the end of DST in 2019), EU member countries could determine whether they want to move permanently to DST or stay on standard time.


he value of DST remains a heated debate. Clear benefits are the increase in evening daylight and the resulting decrease in robbery crimes. However, DST does have negative impacts on our sleep and the economy. As for the effect of DST on energy consumption and traffic accidents, the evidence remains mixed.

Whichever side of the DST debate you’re on, it does appear that one side is winning out over the other, as more countries continue to drop DST in favor of a single-time schedule year-round.

If you live somewhere that observes DST, the best thing you can do to minimize the impact on your sleep and your overall health is to prepare. Just like you might do to avoid jet lag, start gradually shifting your schedule to get used to the time change before it actually happens. Then, once it’s here, you’ll be a lot less tired and out of sorts than the rest of your friends.

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