The switch from standard time to daylight saving time sparks an annual debate over whether the U.S. should pick one time and stick to it.

In March, the Senate took a side, approving the Sunshine Protection Act, which aims to make daylight saving time permanent, beginning in 2023. The act still has to go to the House and the president.

Shifting back and forth between times has been associated with an increased risk of heart attacks and motor vehicle crashes — especially in the spring, says Charles Czeisler, chief of the Division of Sleep And Circadian Disorders at Brigham and Women’s Hospital. Shifting to one time could cut down on these effects and increase productivity. But Czeisler says there’s a problem with the Senate’s legislation: It settles on the wrong time.

Permanent daylight saving time would move everyone in the U.S. one timezone eastward, he explains. People in California would move to Mountain Time, for example, and folks on the East Coast would shift to Atlantic Time.

“There’s extensive research that being on the western edge of a time zone increases the risk of multiple different cancers,” Czeisler says. “A time zone is 15 degrees wide, and every five degrees that an individual lives westward within a time zone increases risk of certain types of cancers in a startlingly high manner.”

Research shows liver cancer risk increased by 11% for every five degrees westward in a time zone a person lived — so the risk could increase by 30% if everyone moved one time zone east, he says. Breast cancer increased by 5% for every five degrees west, which could result in a 15% increase in risk under permanent daylight saving time.

The body’s circadian clock controls the timing of various physiological functions, such as the release of melatonin. On top of promoting sleep, the hormone slows down the growth of cancer, Czeisler says.

Moving to permanent daylight saving time would require everyone to wake up an hour earlier relative to the time the sun rises. Discussion around daylight saving time has focused on the extra light in the evening but Czeisler and others argue this overlooks the downsides.

“We may think that we’re not affected by the solar environment in which we live, but the brightness of the sun outdoors is much more powerful than any of the indoor lights that we have,” he says. “And it still elicits a strong effect on the body.”

Reasons for keeping the time change often involve some long-standing myths. Many people believe the misconception that daylight savings time was something that farmers asked for. But farmers advocated against it because the yearly change would mess with the natural circadian rhythms of their cattle.

And it’s not true that daylight saving time saves energy, Czeisler says. Author Michael Downing’s book “Spring Forward: The Annual Madness of Daylight Saving Time” explains that the golf industry lobbied for daylight saving time to increase profits.

Arizona made standard time permanent in part because daylight saving time ended up causing increased energy use from air conditioners, Czeisler says.

The U.S. has switched to permanent daylight saving time in the past, both during the energy crisis of the 1970s and in World War II — but both instances ended with a return to standard time.

The conversation around sleep tends to focus on getting enough of it, but Czeisler says the consistency of when we go to sleep and wake up matters.

“Maintaining a consistent bedtime and a consistent wake time help stabilize our internal circadian rhythms and keep them in sync with the 24-hour day,” he says. “And that’s one of the reasons why it’s important to avoid the kinds of shifts that are associated with shifting our time zones. “

A permanent switch to daylight saving time would also erode some of the progress made in delaying high school start times.

The American Academy of Pediatrics recommends high schools start no earlier than 8:30 a.m. standard time. Biologically, permanent adoption of daylight saving time would mean an 8:30 a.m. class starts at 7:30 a.m.

“That has already been shown to interfere with academic performance and increase motor vehicle crashes of high school students and so on,” Czeisler says.

If the country adopts permanent daylight saving time, Czeisler predicts that people won’t want to wake up an hour earlier every day. To make up for lost time during the week, people may sleep later on the weekends, which will increase what’s called social jetlag and chronic sleep deprivation.

“That’s going to propel their circadian systems to a later hour,” he says, “and make it more difficult for them to go to sleep at a time that is sufficient for them to get enough sleep before the alarm clock is going to go off in the morning.”

Karyn Miller-Medzon produced and edited this interview for broadcast with Todd Mundt. Allison Hagan adapted it for the web.

This article was originally published on WBUR.org.

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