It's no secret that we live in a sleep-deprived society. More than a third of Americans don't sleep enoughdefined as a minimum of seven hours per day. It's not just the US: much of the developed world is in a similar situation. “People have a hard time getting up,” says Eva Winnebeck, a chronobiologist at the University of Surrey in the UK. “People have a hard time getting up. There's a lot of alarm clock use and a lot of sleep deprivation.” (Rule of thumb: If you need an alarm to wake up, it probably means you're not getting enough sleep.)
So why do we compound the problem of sleep deprivation twice a year by switching to Daylight Saving Time? Why do we lose track of our internal clocks in the spring and fall—November 2 for Americans?
Experts say we should stop this practice. American Academy of Sleep Medicine (AASM) and various European sleep and rhythm medicine societies spoke out against clock switching. “These seasonal time changes should be abolished,” the AASM said in a statement, while the European groups also pushed for a common standard time because keeping one time throughout the year could help us better navigate the sun. But although these organizations made themselves known, governments resisted changing the status quo.
What sleep deprivation does to the body
Public health researchers have found that sleep deprivation leads to more car accidents, greater risk of diabetes and even higher risk of heart attacks. This is because long-term sleep deprivation affects the body's biology in ways that go beyond just feeling sleepy. This can raise your blood pressure and increase risky behaviour, and can also mean a disruption in the connection between your body's internal clock and the sun, which is especially common among shift workers.
Biological processes that should occur at different times begin to overlap, while those that should be synchronized begin to spread out. increased risks cardiovascular disease and cancer in people who work at night.
Why do we keep changing the clocks?
This biannual sleep disorder is not that old. It is a policy set by governments, and current practice in the US dates back to 1966 with the passage of the Uniform Time Act. Before this, during the world wars, the United States temporarily resorted to using clocks to save energy. The idea was to take people's daily activity period and move it so that most of it occurs during natural daylight hours, saving on fuel costs.
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It resumed in the 1960s when the Interstate Commerce Commission, which regulated transportation, insisted on a standardized approach to time. Companies operating planes and trains across national borders needed a clear understanding of what time was where, and the Act made regular daylight saving time mandatory by law.
As of 2025, most Americans observe daylight saving time eight months a year, from March to November. Standard time lasts only four months. (Hawaii and Arizona, among other localities, do not observe daylight saving time.)
Seasonal shifts are natural, but not these shifts
It's not that human biology requires day and night to remain constant.
Because the Earth's axis is tilted in many places daylight waxes and wanes within a year. This is especially noticeable further from the equator; in Northern England, for example, there is less than eight hours of sunshine on the shortest day of the year, and more than 10 hours in San Antonio.
Research has shown that people may be naturally wired to change their sleep duration depending on the season, says Manuel Schabus, a professor at the University of Salzburg in Austria who studies sleep. IN 2015 documentThe researchers found that people in three different pre-industrial societies rose shortly before sunset year-round and typically fell asleep about three hours after sunset. In summer they stayed awake about an hour longer than in winter. AND research It shows people from industrialized societies going on hikes without access to artificial light as they come into rhythm with the sun.
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But daylight saving time requires unnatural changes that put many people at odds with the sun's signals, says chronobiologist Martha Merrow, a professor at Ludwig Maximilian University of Munich.
With daylight saving time, “you need to use your alarm more often,” she says. “We should look for ways to avoid using an alarm clock. Every time we use an alarm clock, we are depriving ourselves of sleep.”
However, it is difficult to determine how to assess the biological consequences of these policies. “It’s very difficult to say how much benefit it provides to any given person,” Winnebeck says. “But it affects everyone in society. It happens for eight months of the year. And we do it for years on end with millions of people.”
This could be the circadian equivalent of eating unhealthy food every day for years, she says. “The problem is proving it. It's very difficult.”
Guess about a data problem
Does living with daylight saving time most of the year affect your health? “It's a difficult question to answer,” says Dr. Elizabeth Klerman, a professor of neurology at Harvard Medical School, but there are some hints. research which compare health indicators across time zone boundaries. This is because people living on the eastern edge of the time zone are in a privileged position: solar time and the time on their clocks coincide more accurately. Residents of the western region suffer from a discrepancy between solar time and clock time. Essentially, it's similar to what daylight saving time does, Klerman says.
These studies show an interesting pattern: “There are more cancer cases on the western edge of the time zone,” she says. There are also higher rates of obesity and diabetes, which are associated with disruption of circadian rhythms. People are also more likely to suffer from sleep deprivation.
This suggests that daylight saving time may have real health consequences.
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There are a number of studies that support the short-term risks of daylight saving time, such as an increase in traffic accidents the day after a shift. Russell Foster, a circadian neuroscientist at the University of Oxford who recently reviewed much of this evidence, says the research is generally not as strong as you might think.
However, departure from standard time does correlate with surge in heart attacks; the transition back to standard mode, back in sync with the sun, correlates with decline.
Life according to solar time
Eliminating seasonal time changes is a recurring topic of public policy debate. In 2019 the European Parliament voted to end this practice. “But there’s still no progress,” says Schabus. It has been proven that it is difficult to agree what to do instead: Will some EU countries adopt some kind of permanent daylight saving time all year round? Will others use standard time?
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Some sleep scientists wonder if something more radical might ever be possible. What if we could actually keep track of solar time without artificial constructs like daylight saving time, or even time zones? If we did this, the sun would be directly overhead at noon, and wake-up time could follow the sun throughout the year. “Until Europe had train systems, people used solar time,” Murrow says. When it comes to facilitating long-distance coordination (what time zones are currently used for), perhaps computer tools could do the math for us, she muses.
Schabous, for his part, also favors a sleep-wake cycle that can change depending on the season, and points to the increased focus on flexible working in the EU as a potential boon for those interested in following the sun. “I think our bodies find it easiest to follow these rules,” he said. After all, this is how we evolved.
