The House still needs to pass the so-called Sunshine Protection Act, but if it succeeds, the time Americans live on during the summer—four hours behind Greenwich Mean Time (GMT)—would now be the standard time across the U.S. year-round. That means later sunrises and sunsets.

Yet sleep scientists argue the choice of daylight saving time over standard time—in other words, choosing the “spring forward” rather than “fall back” time—would leave Americans permanently out of sync with their natural schedule and potentially lead to a range of health issues.

Why do we have daylight saving time?

First applied consistently across the U.S. in 1966, daylight saving is an idea whose time may have passed.

Originally, daylight saving was meant to reduce energy consumption, by setting clocks forward thus extending the hours of daylight further into the evening. With more sunlight, people require less electricity for artificial lighting. However, research suggests that the changing ways we consume energy means daylight saving time no longer saves enough electricity to be meaningful.

In fact, one 2008 study found that moving clocks forward actually increased electricity consumption as people started using more power-hungry appliances, like air-conditioning, later into the evening.

The U.S. population has also trended south in recent decades, with population growth in states like Arizona, Texas, and Florida significantly outstripping their Northern counterparts. Southern states see a smaller seasonal difference in daylight hours, which reduces the need to “save” daylight. For example: northernly Detroit gets over 15 hours of sunlight in the summer and only nine hours in winter. Southernly Austin gets 14 hours of daylight in summer and 10 hours in winter.

Should we stop changing our clocks?

Some researchers blame the switch between standard and daylight saving time for a number of social ills, including lost productivity and increased health stress, as people’s bodies adjust to the time change.

One study found a small but significant increase in road accidents on the Monday after the switch to summer time, as the lost hour of sleep affected people’s driving ability. Other studies found the rate of workplace injuries and even heart attacks tends to increase shortly after the U.S. “springs forward.”

Retailers also support a switch to permanent daylight saving time. A 2017 report from JPMorgan Chase found that shoppers spent 3.5% less in stores in the month immediately following the “fall back” switch to standard time, as earlier sunsets encouraged people to go home rather than shop.

But perhaps most importantly, Americans generally hate changing the time on their clocks. A 2019 poll found that seven in 10 Americans would prefer leaving their clocks alone. 

Is daylight saving time bad?

In their fight to “protect sunshine,” the U.S. Senate had the choice of making either standard time or daylight saving time permanent. The Senate chose to keep daylight saving, but that might prove to be the worse of the two choices, with potentially worse health outcomes.

Many sleep scientists support standard time over daylight saving, as the latter more closely aligns with the natural day—and thus our natural body clocks.

Adopting daylight saving time as standard “leaves us permanently out of sync with the natural environment,” said Joseph Takahashi of the University of South Texas to the New York Times. 

Scientists are also concerned that forcing people to wake up earlier and fall asleep later than their natural body clocks dictate may worsen sleep deprivation, which is linked to increased rates of obesity, diabetes, dementia, and other health issues.

Studies have found that people working night shifts—forced to work at times that are out of sync with their natural sleep schedule—have higher rates of heart disease and cancer than than those who work daytime hours.

Why didn’t we do this sooner?

The U.S. has actually tried to make daylight saving time permanent once before.

The U.S. tried a permanent switch to daylight saving time in 1974 to save energy during the oil embargo by the Organization of Arab Petroleum Exporting Countries. But after complaints from parents about schools starting in the dark, and a spate of well-publicized road accidents involving children, the U.S. abandoned the practice by October 1974. 

Sleep deprivation is already endemic among adolescents due to teenagers having to wake up “early” to go to school. Teenagers have a naturally later sleep cycle than children and adults, which means they should wake up later in the day to stay in sync with their body clocks.

U.S. Sen. Marco Rubio, who cosponsored the Protecting Sunshine Act, suggested that schools should start later in response to concerns that students would be going to school in the dark.

“We start school in this country at the worst possible time for adolescents,” Rubio said.