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The Health Effects of Daylight Savings Time

Research shows that changing the clocks has negative effects on well-being.

Key points

  • Daylight saving time has been proven to lead to negative health consequences.
  • The time shift has been linked to increases in heart attacks, traffic accidents, and mental health problems.
  • The research on whether the time change leads to energy saving is mixed.
Source: Reddogs

Getting out of bed for a particular week in mid-March is often associated with heavy eyelids and foggy brains – the consequences of losing an hour of sleep when we push our clocks forward for daylight saving time.

This year, the week after the clocks sprung forward, the U.S. Senate quickly and unanimously passed a bill to make daylight saving time permanent, eliminating the ritual of changing our clocks twice a year. (To become law, the bill still has to make it through the U.S. House of Representatives and be signed by the President).

It turns out, there is plenty of evidence to back up the Senate’s action. In fact, a large body of research demonstrates that daylight saving time harms our health and well-being.

First, a little history: It’s a myth that farmers first requested daylight saving time; they have actually lobbied against it for years. It was Benjamin Franklin who first proposed the shift in 1784 to conserve candles. But the time change wasn’t implemented in the United States until 1918 in an effort to save energy at the start of World War I.

Modern research has clearly demonstrated that daylight saving time leads to sleep loss – and not just when our clocks spring forward. Even in the fall, when we supposedly “gain” an hour of sleep, the data show that most people simply wake up earlier, leading to a net loss of sleep. There is evidence that these sleep disruptions last five days or longer. Changing our clocks results in an entire work week during which most of the country is more sleep-deprived than usual.

And sleep deprivation leads to health problems: There is solid data showing that moving clocks forward in the spring leads to an increase in heart attacks. A meta-analysis of six studies including more than 87,000 cases found a significant increase – ranging from 4 to 29% – in the risk of having a heart attack the week after the spring time change. Researchers believe this increase is related to the change in our circadian rhythm and the general disruption of biological processes.

A broader review also found increases in the incidence of emotional and behavioral disorders, stress-related immune disorders, and accidents involving injuries. And a separate study found that moving the clocks back in the fall results in an 11% increase in depressive episodes.

There is also some evidence that daylight saving sleep loss leads to more traffic accidents. One study analyzed more than 730,000 fatal traffic accidents in the U.S. from 1996 to 2017. Researchers found that the spring transition increased fatal traffic accident risk by 6% during the week after the spring time change. The risk of these accidents is highest in the morning, and also in locations that are further west in their respective time zones.

Another review, however, found less concrete evidence that daylight saving time changes lead to traffic accidents. Combining 24 studies, researchers found mixed evidence. Some data point to an increase in traffic accidents. But over the long-term, researchers actually found fewer traffic accidents during the entirety of daylight saving time, when there is more daylight in the evenings.

Still, the health effects of changing our clocks are so clear that the American Academy of Sleep Medicine has called for getting rid of daylight saving time for the past two years.

What about that energy savings? Researchers have studied that, too. A small study of households in Ontario, Canada found that daylight saving time leads to a 1.5% reduction in residential energy consumption. A larger but older literature review found mixed evidence, with some studies demonstrating energy savings, but others finding no effect.

The take-home message: Daylight saving time clearly has negative consequences for public health. Even with modest energy savings, it would be prudent for Congress to do away with these time changes.