In the 108-year history of daylight saving time in the United States, the country has three times moved to institute it year-round: during each of the two world wars and in 1973-74.

Now, after a 2022 attempt to reintroduce this policy floundered, the U.S. House of Representatives on July 14, 2026, passed the , which would put the country permanently on daylight saving time. by a wide margin, 308-117, with President Donald Trump publicly backing the measure. It will now be considered by the Senate.

With the exception of Arizona and Hawaii, which observe standard time year round, the U.S. observes seasonal daylight saving time, moving clocks ahead by one hour each March and turning them back each November.

Nearly two-thirds of Americans would like to , compared to 21% who aren’t sure and 16% who would like to keep moving their clocks back and forth, according to a 2026 poll.

But the effects go beyond simple inconvenience. Researchers are discovering that “springing ahead” each March is connected with serious negative health effects, including an uptick in and . In contrast, the fall transition back to standard time is not associated with these health effects, as my co-authors and I noted in a .

I’ve studied the pros and cons of these twice-annual rituals for more than five years as a and the director of Vanderbilt University Medical Center’s sleep division. It’s become clear to me and many of my colleagues that the transition to daylight saving time each spring affects health immediately after the clock change and also for the nearly eight months that .

The strong case for permanent standard time

Americans are split on whether they or .

However, the two time shifts – jolting as they may be – are not equal. Standard time most closely approximates natural light, with the Sun directly overhead at or near noon. In contrast, during daylight saving time from March until November, the clock change resulting from daylight saving time causes natural light to be present one hour later in the morning and one hour later in the evening according to clock time.

Morning light is essential for helping to set the body’s natural rhythms: It . Morning light also boosts mood – light boxes simulating natural light are prescribed for morning use .

Evidence suggests that making standard time permanent could have health benefits – perhaps because standard time would expose people to more morning light.

Although the exact reasons why light activates us and benefits our mood are not yet known, this may be due to light’s effects on , a hormone that or the effect of , a part of the brain involved in emotions.

Adolescents also may be , sports and social activities. For instance, many or earlier. This means that during daylight saving time, many young people get up and travel to school in pitch darkness.

The body of evidence makes a good case for adopting permanent standard time nationwide, as I testified at a and argued in a for the Sleep Research Society. The American Medical Association has also .

The biggest advantage of daylight saving time is that it provides an extra hour of light in the late afternoon or evening, depending on time of year, for sports, shopping or eating outside. However, exposure to light later into the evening for almost eight months during daylight saving time comes at a price. This extended evening light delays the brain’s release of melatonin, the hormone that promotes drowsiness, which in turn interferes with sleep and .

Because puberty also causes , meaning that teenagers have a delay in the natural signal that helps them fall asleep, adolescents are from the extended evening light. This shift in melatonin during puberty lasts into our 20s.

The ‘western edge’ effect

Geography can also make a difference in how daylight saving time affects people. One study showed that people living on the western edge of a time zone, who get light later in the morning and later in the evening, than their counterparts on the eastern edge of a time zone.

This study found that western-edge residents had higher rates of obesity, diabetes, heart disease and , as well as lower per capita income and higher health care costs. Other research has found that on the western edge of a time zone.

Scientists believe that these health problems may result from a .” Circadian misalignment refers to a mismatch in timing between our biological rhythms and the outside world. In other words, the timing of daily work, school or sleep routines is based on the clock, rather than on the Sun’s rise and set.

This video takes a deeper dive – all the way back to 1895 – into the history of daylight saving time.

A brief history of daylight saving time

during World War I and World War II, and of the early 1970s.

The idea was that having extra light later into the afternoon would save energy by decreasing the need for electric lighting. This idea has since been , as heating needs may increase in the morning in the winter, while air conditioning needs can also increase in the late afternoon in the summer.

Another pro-daylight saving argument has been that crime rates drop with . While this has been proved true, the change is very small, and the benefits to society from lower rates of crime.

After World War II, designating the start and end dates for daylight saving time fell to state governments. Because this created many railroad scheduling and safety problems, however, Congress passed the . This law set the nationwide dates of daylight saving time from the last Sunday in April until the last Sunday in October. In 2007, to expand the period in which daylight saving time is in effect from the second Sunday in March to the first Sunday in November – dates that remain in effect today.

The Uniform Time Act allows states and territories to opt out of daylight saving time, however. Arizona and Hawaii are on permanent standard time, along with Puerto Rico, the U.S. Virgin Islands, Northern Mariana Islands, Guam and American Samoa.

Several U.S. states have legislation and resolutions under consideration to support permanent standard time, while many others have been or are . Among all these efforts combined, state-level measures in support of permanent standard time have increased .

In March 2022, the U.S. Senate in a bid to . But the House did not move forward with this legislation. Even as the current version of the Sunshine Protection Act awaits consideration in the Senate, a bipartisan countermeasure, the , introduced in the House on July 9, would restore permanent standard time as the nation’s default clock.

Now, it’s up to legislators to decide whether to end the time shift altogether, and whether to choose permanent standard or daylight saving time.

This is an updated version of an article , and .

Original article
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