Health Advice



Could the days of ‘springing forward’ be numbered? A neurologist and sleep expert explains the downside to that borrowed hour of daylight

Beth Ann Malow, Vanderbilt University, The Conversation on

Published in Health & Fitness

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 causes us to sleep less overall.

Because puberty also causes melatonin to be released later at night, meaning that teenagers have a delay in the natural signal that helps them fall asleep, adolescents are particularly susceptible to sleep problems from the extended evening light. This shift in melatonin during puberty lasts into our 20s.

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, got less sleep 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 breast cancer, as well as lower per capita income and higher health care costs. Other research has found that rates of certain other cancers are higher on the western edge of a time zone.

Scientists believe that these health problems may result from a combination of chronic sleep deprivation and “circadian misalignment.” 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.

Congress instituted year-round daylight saving time during World War I and World War II, and once again during the energy crisis of the early 1970s. But the popularity of year-round daylight saving time fell from 79% to 42% after it went into effect in January 1974, largely due to safety concerns about children going to school in the dark.

The idea at that time was that having extra light later into the afternoon would save energy by decreasing the need for electric lighting. This idea has since been proved largely inaccurate, 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.

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 Uniform Time Act in 1966. This law set the nationwide dates of daylight saving time from the last Sunday in April until the last Sunday in October. In 2007, Congress amended the act 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.

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


As of March 2024, 17 states have passed laws to adopt year-round daylight saving time. But federal law requires that they need to wait for Congress, and in some cases also neighboring states, to act. More than two dozen states introduced legislation related to the clock change in 2023, but no laws were passed.

Meanwhile, proposed legislation and resolutions for permanent standard time have increased from 15% in 2021 to 37% in 2024.

In March 2022, the U.S. Senate passed the Sunshine Protection Act in a bid to make daylight saving time permanent. But the House did not move forward with this legislation. Florida Sen. Marco Rubio reintroduced the bill on March 1, 2023, but this bill has not progressed.

The spike in activity among states seeking to break from these twice-yearly changes reflects how more people are recognizing the downsides of this practice. Now, it’s in the hands of legislators to decide whether to end the time shift altogether and to either choose a full year of having clocks more aligned with the sun or to artificially extend the day for more than half the year, for better or for worse.

This is an updated version of an article originally published on March 10, 2022.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and analysis to help you make sense of our complex world.

Read more:
Springing forward into daylight saving time is a step back for health – a neurologist explains the medical evidence, and why this shift is worse than the fall time change

100 years later, the madness of daylight saving time endures

Beth Ann Malow is the Sleep Research Society representative to the Coalition for Permanent Standard TIme.


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