Daylight saving time increases the risk of death, heart attacks and car accidents

• Daylight saving time is a killer, scientists say.
• One-third of the world's population and most U.S. states observe daylight saving time.
• Daylight saving time is linked to an increase in heart attacks and car accidents.

Summer is over and this Sunday it's time to turn back the clocks and end Daylight Saving Time for the year.

Doctors and scientists say this could save some lives, especially because people will get much-needed extra sleep.

The annual ritual in which we “win” an hour of evening light in the summer by moving the clocks forward an hour each spring may seem like a harmless shift. Most Americans love it.

But it's actually incredibly controversial, and doctors, including those at the American Medical Association, say the damage it does to our health isn't worth it.

Here's what daylight saving time is, why it was developed in the first place, and what we now know about its health effects:

When is summer time?

In US states that observe daylight saving time, the clocks change each year on the second Sunday in March and the first Sunday in November.

In spring, the clocks “jump forward” an hour at 2:00 a.m. and immediately adjust to 3:00 a.m

In the fall, the clocks go back one hour at 2:00 a.m. and immediately set to 1:00 a.m

This year we lost an hour on Sunday March 10th. On Sunday November 3rd we will gain an hour.

What is the purpose of daylight saving time?

Daylight saving time was originally invented to save energy in the evenings and was introduced in Germany during World War I.

Today, about a third of the world's population takes part in the twice-yearly ritual of changing the clocks, and most of these countries are in Europe.

Not everyone in the US follows Daylight Saving Time. Hawaii and Arizona ignore it and use standard time all year round. These states argued that it made less sense to change clocks if you lived near the equator, where the sun rises and sets at approximately the same time every day.

So does it save energy?

Recent research suggests that this probably won't save us megawatts of electricity – but it could cost us. The state of Indiana did not implement daylight saving time until 2006. One study found that people spent $7 million more per year on electricity bills after the switch than before. Another study found that workers are less productive at the start of daylight saving time.

However, there is evidence that, at least in certain climates, additional evening light can reduce crime and increase the time people spend exercising outdoors.

Increase in heart attacks and strokes

Every year on the Monday after Daylight Saving Time goes into effect in the spring, hospitals across the U.S. report a 24% increase in heart attack visits.

Just a coincidence? Probably not. Doctors see an opposite trend every fall: The day after we turn back the clocks, heart attack visits drop 21% as many people enjoy a little more time in bed.

In Finland, researchers found an 8% increase in ischemic strokes in the two days after the clocks were moved forward.

It's not exactly clear why this happens, but researchers suspect it could be a combination of sleep problems, stress at the start of the work week, and underlying medical conditions.

“That's how fragile and vulnerable your body is to just one hour of sleep loss,” sleep expert Matthew Walker and author of “How We Sleep” previously told Business Insider.

Disruption of our natural hormonal cycle

The reason turning the clock forward and back is bad for us is because of disrupted sleep patterns.

The human body has its own internal clock: the “circadian rhythm,” which works in harmony with the rest of the outside world. When we're exposed to sunlight, our bodies release hormones that keep us alert, speed up our metabolism, and stimulate digestion and hunger so we have the energy to be active during the day. (This is why jet lag experts recommend going outside around sunrise or sunset to adjust your body to local sleep patterns.)

As darkness falls, our bodies release melatonin, the hormone that makes us sleepy. At this time, our bodies also release growth hormones, our memories solidify, and our body temperature drops to conserve energy.

The Sleep Research Society argues that getting up and starting our days in the dark disrupts our body's natural hormone production and that triggering this change once a year can increase our risk of obesity, diabetes, mood disorders, cardiovascular problems and life-threatening accidents . A study found that daylight saving time may cause a temporary increase in suicides. (Sleep doctors are therefore also calling for an end to night shift work.)

In a statement calling for the abolition of daylight saving time, the American Medical Association said it can take months for our bodies to adjust to the new sleep cycle.

Increase in car accidents

We're also more prone to making more deadly mistakes on the road: A study of over 700,000 car accidents from the mid-1990s to 2017 found a 6% increase in accidents the week after Daylight Saving Time went into effect.

Researchers believe this is partly due to lack of sleep among drivers and pedestrians, as well as a lack of visibility.

DST also leads to more reports of workplace injuries. A 23-year study of miners found that both the number and severity of their injuries rose reliably each year on the Monday after Daylight Saving Time began, and other workers lost about 40 minutes of sleep.

Some lawmakers want permanent daylight saving time — others want standard time year-round

The political debate over daylight saving time is heated, unscientific and deeply divided.

According to the National Conference of State Legislatures, there are at least 20 states that have passed or are considering legislation to move to permanent daylight saving time. And just as many states are considering legislation to abolish daylight saving time and permanently switch to standard time. There's some messy overlap here – a dozen states have bills considering both approaches. There are bills in many states that say they will switch to the same time as their neighbors are on.

California is a unique case. In the 2018 midterm elections, voters decided to eliminate the annual time change and permanently switch to daylight saving time. Then, in early 2024, lawmakers opposed to daylight saving time introduced a bill to switch to permanent standard time — but both options got stuck in committee meetings and never really advanced.

Switching to permanent daylight saving time requires a green light from Congress, but states do not need federal approval to switch to permanent standard time.

The federal government is considering permanent daylight saving time in 2022. In fact, the Sunshine Protection Act introduced by GOP Sen. Marco Rubio passed unanimously in the Senate but failed in the House.

Health and sleep experts expressed relief. They said the entire country should follow the example of Hawaii and Arizona and wondered whether Rubio and his colleagues had misunderstood which time system was better.

“When we saw that, it was kind of like an 'oopsie daisy,'” said Dr. Akinbolaji Akingbola, a sleep expert at the University of Minnesota Medical School, previously told Business Insider. “It was pretty clear to all of us that standard time would be the better choice.”