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

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The Strong Case for Permanent Standard Time

As people in the U.S. prepare to set their clocks ahead one hour on Sunday, March 12, I find myself bracing for the annual ritual of media stories about the disruptions to daily routines caused by switching from standard time to daylight saving time.

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About one-third of Americans say they don’t look forward to these twice-yearly time changes. And nearly two-thirds would like to eliminate them completely, compared to 21% who aren’t sure and 16% who would like to keep moving their clocks back and forth.

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 heart attacks and teen sleep deprivation. In contrast, the fall transition back to standard time is not associated with these health effects.

I’ve studied the pros and cons of these twice-annual rituals for more than five years as a professor of neurology and pediatrics 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 Americans remain on daylight saving time.

The Case for Standard Time

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 wakes us up and improves alertness. Morning light also boosts mood – light boxes simulating natural light are prescribed for morning use to treat seasonal affective disorder.

The body of evidence makes a good case for adopting permanent standard time nationwide. The American Medical Association recently called for permanent standard time, and in late 2022, Mexico adopted permanent standard time, citing benefits to health, productivity, and energy savings.

The Disadvantages of Daylight Saving Time

The biggest advantage of daylight saving time is that it provides an extra hour of light in the late afternoon or evening, depending on the 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.

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, 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.

A Brief History of Daylight Saving Time

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. 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 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.

Another pro-daylight saving argument has been that crime rates drop with more light at the end of the day. While this has been proved true, the change is very small, and the health effects appear to outweigh the benefits to society from lower rates of crime.

Conclusion

As the U.S. prepares to "spring forward" into daylight saving time, it’s essential to recognize the negative health effects that this time change has on our bodies and brains. The evidence is clear: adopting permanent standard time would be a step forward for health.

FAQs

Q: What are the negative health effects of daylight saving time?
A: Research has linked daylight saving time to increased heart attacks, teen sleep deprivation, and chronic sleep deprivation.

Q: Why is morning light important?
A: Morning light helps to set the body’s natural rhythms and improves alertness. It also boosts mood.

Q: Why are teenagers particularly susceptible to sleep problems during daylight saving time?
A: Puberty causes melatonin to be released later at night, making it harder for teenagers to fall asleep and stay asleep.

Q: Are there any benefits to daylight saving time?
A: While there are some benefits to having extra light in the late afternoon or evening, these benefits are largely outweighed by the negative health effects.

Q: Have any countries adopted permanent standard time?
A: Yes, Mexico adopted permanent standard time in late 2022, citing benefits to health, productivity, and energy savings.

Q: Are there any ongoing efforts to eliminate daylight saving time?
A: Yes, there are ongoing efforts at the state and national levels to eliminate daylight saving time or adopt permanent standard time.