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Jumping forward to daylight saving time is a step backwards for health – a neurologist explains the medical evidence and why this shift is worse than the fall time change


As people across the US prepare to move their clocks forward one hour on Sunday, March 12, 2023, I find myself bracing for the annual ritual of media stories about the disruptions of the daily routine caused by changing standard time to summer time.

About a third of Americans say they don’t look forward to these biennial time changes. And almost two thirds would like to eliminate them completelycompared to 21% who are not sure and 16% who would like to keep moving the clock back and forth.

But the effects go beyond discomfort. Researchers find that “jumping forward” in March is associated with serious negative health effects, including an uptick heart attacks And sleep deprivation in teens. In contrast, the regressive transition to standard time is not associated with these health effects, as my co-authors and I noted in a 2020 commentary.

I have studied the pros and cons of these biennial rituals for over five years as a professor of neurology and pediatrics and the director of the sleep department at Vanderbilt University Medical Center. It has become clear to me and many of my colleagues that the transition to summer time each spring has health implications immediately after the clock change and also during the nearly eight months that Americans stay on daylight saving time.

The strong case for permanent standard time

Americans are divided on whether they prefer permanent summer time or permanent standard time.

However, the two time shifts, as shocking as they may be, are not equal. Standard time most closely approximates natural light, with the sun directly overhead at or around noon. Unlike summer time from March to November, the clock change due to daylight saving time ensures that natural light is present one hour later in the morning and one hour later in the evening according to the clock time.

Morning light is essential to help regulate the body’s natural rhythms: the wakes us up and improves alertness. Morning light also improves mood – light boxes that simulate natural light are prescribed for morning use to treat seasonal affective disorder.

While the exact reasons why light activates us and benefits our mood are not yet known, it may be due to the effects of light on increasing levels of cortisola hormone that modulates the stress response or the effect of light on the amygdalapart of the brain involved in emotions.

Adolescents can also be chronically sleep deprived due to school, sports, and social activities. Many, for example children go to school around 8 o’clock or earlier. This means that many young people get up in the summer time and go to school in pitch darkness.

The amount of evidence makes a good case for introducing permanent standard time across the country, as I testified at a March 2022 Congressional hearing and argued in a recent position statement for the Sleep Research Society. The American Medical Association recently called for permanent standard time. And at the end of 2022, Mexico has adopted permanent standard time,, citing health benefits, productivity and energy savings.

In 2023, the clock will jump forward one hour at 02:00 on Sunday, March 12. Sunday, November 5 at 2 a.m.
iam2mai/iStock via Getty Images Plus

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 exercising, shopping or eating outside. However, exposure to light later in the evening for nearly eight months during daylight savings time comes at a price. This extended evening light slows the brain’s release of melatonin, the hormone that promotes drowsiness, which in turn disrupts sleep and sleep. causes us to sleep less overall.

Because puberty also causes melatonin released later in the eveningmeaning teens have a delay in the natural signal that helps them fall asleep are adolescents particularly prone to sleeping problems of the extended evening light. This shift in melatonin during puberty lasts into your twenties.

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 that get light later in the morning and later in the evening, slept less than their counterparts on the eastern edge of a time zone.

This study found that residents of the Western Rim 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 the rates of certain other cancers are higher at the western edge of a time zone.

Scientists believe that these health problems may be due to a combination of chronic sleep deprivation and “circadian misalignment.” Circadian alignment 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 the rising and setting of the sun.

This video goes deeper – all the way back to 1895 – into the history of DST.

A Brief History of Daylight Saving Time

Congress instituted Daylight Saving Time year-round during the First and Second World Wars, and again during the energy crisis from the early 1970s.

The idea was that extra light later in the afternoon would save energy by reducing the need for electric lighting. This idea has been around ever since turned out to be largely inaccurateas the need for heating can increase in the mornings in winter, while the need for air conditioning can also increase in the late afternoon in the summer.

Another pro-argument for daylight savings time is that crime rates are falling more light at the end of the day. While this has proven to be true, the change is very small and the health effects seem to outweigh the benefits to society of lower crime rates.

After World War II, designating the start and end dates for daylight saving time fell to the state governments. However, because this caused many railroad planning and safety problems, Congress approved it Uniform Time Act in 1966. This law sets the national dates for daylight saving time from the last Sunday in April to the last Sunday in October. In 2007, Congress changed the law to extend the period during 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.

However, the Uniform Time Act allows states and territories to waive daylight saving time. Arizona and Hawaii have permanent standard time, as do Puerto Rico, the US Virgin Islands, the Northern Mariana Islands, Guam, and American Samoa.

Now many other states are considering whether to do so stop falling back and jumping forward. Several U.S. states have legislation and resolutions pending to support permanent standard time, while many others have or are taking into account permanent summer time. Legislation and resolutions for permanent standard time increased from 15% in 2021 to 31% in 2023.

In March 2022, the US Senate passed the Sunshine Protection Act in an attempt to make daylight saving time permanent. But the House did not move forward with this legislation. Florida Senator Marco Rubio resubmitted the bill on March 1, 2023.

The spike in activity among states trying to break away from these biennial changes reflects the more people are recognizing the drawbacks of this practice. Now it is up to lawmakers to decide whether to end time shifting altogether and opt for permanent standard or daylight saving time.

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

Merry C. Vega is a highly respected and accomplished news author. She began her career as a journalist, covering local news for a small-town newspaper. She quickly gained a reputation for her thorough reporting and ability to uncover the truth.

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