This weekend marks fall back, the time each year when most people in the US set their clocks an hour earlier as daylight saving time ends.

It’s a rule that seems arbitrary and unnecessary to many, and research shows it can negatively impact our sleep cycles and overall health.

So why do we do it? Here’s a look at the history behind daylight saving time in the US

When does time change?

This year it will be on November 3 at 2 a.m., this Sunday. It is one of the two times a year that the time changes. The exact days are determined by federal law and have shifted over the years. The current dates went into effect in 2007 as part of the Energy Policy Act passed when George W. Bush was president.

Why does time change?

Daylight saving time was originally intended to reduce energy costs during times of war. According to the U.S. Department of Defense, it was first signed into law in the U.S. during World War I on March 1, 1918. The law was repealed after the end of the war and reintroduced during World War II. That led to it being known as “wartime.”

There were no set time rules across the country from the end of World War II through 1965. The Uniform Time Act of 1966 put daylight saving time into federal law and established official time zones, ending the confusion over what time it was in different parts of the country.

Does daylight saving time really save energy?

A 2008 study by the U.S. Department of Energy, after the daylight saving season was extended by four weeks under President Bush, found that electricity savings during the additional weeks were about 0.5% per day, or 0.03% of total electricity consumption for the whole year.

Critics say the savings are minuscule and stem from larger economic motivations, including lobbying by retail companies, which argue that daylight saving time leads to more people shopping and doing other activities in the evening.

Whose idea was it?

There is also debate about where the idea of ​​DST came from in the first place. Some nod to Benjamin Franklin, but many historians credit a New Zealand man who first proposed daylight saving time in an 1895 article. Germany was the first country to implement it in 1916, during World War I.

How does the changing time affect our health?

Scientists have linked changing times twice a year to various health and safety issues. For example, a 2016 study found that stroke rates are 8% higher in the first two days after both time changes. A 2020 study linked the spring change to a 6% increase in traffic accidents. And a 2017 study found that the fall time change resulted in an 11% increase in symptoms of depression reported in hospitals.

Doctors believe that the reason for these effects is due to a lack of sunlight and disruptions to the circadian rhythm. Some experts think it’s better to stick to daylight saving time all year round, while others think standard time would always be best.

What is the public opinion on ‘falling back’ and ‘leaping forward’?

A 2022 survey by YouGovAmerica found that 59% of people in the US supported daylight saving time year-round. Nineteen percent were against, while 22% had not yet made a decision.

A move to temporarily make daylight saving time permanent for two years amid a nationwide gas shortage was reversed after just a few months in 1974 due to public outcry, including concerns about children going to school after dark and an increase in the number traffic accidents.