Changing the clocks to daylight saving time is bad for your health

The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.

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

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

But the results go beyond mere discomfort. Researchers are finding that ‘springing forward’ each March is linked to serious negative health effects, including an increase in heart attacks and sleep deprivation in teenagers. In contrast, the fall to standard time is not associated with these health effects, as my colleagues and I noted in a 2020 commentary.

I’ve studied the pros and cons of these twice-yearly rituals for more than five years as a professor of neurology and pediatrics and director of sleep at Vanderbilt University Medical Center. It is clear to me and many of my colleagues that the switch 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 strong case for permanent standard time

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

However, the two temporal shifts – as jarring as they are – are not equal. Standard Time most closely approximates daylight, with the sun just above or near noon. In contrast, during daylight saving time from March to November, the clock change resulting from daylight saving time causes daylight to be one hour later in the morning and one hour later in the evening according to clock time.

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

Although the exact reasons why light activates us and benefits our mood are not yet known, it may be due to the effect of light on increasing levels of cortisol, a hormone that regulates the stress response, or the effect of light on the amygdala , a part of the brain involved in emotions.

Teenagers may also be chronically sleep deprived due to school, sports and social activities. For example, many children start school around 8 am or earlier. This means that during daylight saving time, many young people get up and travel to school in complete darkness.

The body of evidence justifies the adoption of permanent national standard time, as I testified at a March 2022 congressional hearing and argued in a recent position statement for the Society for Sleep Research. The American Medical Association recently called for permanent regular time. And in late 2022, Mexico adopted permanent standard time, citing health, productivity and energy-saving benefits.

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 out. However, exposure to light later at night for nearly eight months during daylight saving time comes at a price. This prolonged evening light delays the brain’s release of melatonin, the sleep-promoting hormone, which in turn interferes with sleep and makes us sleep less overall.

Because puberty also causes melatonin to be released later at night, meaning teens have a delay in the natural signal that helps them sleep, teens are especially susceptible to sleep problems from prolonged evening light. This melatonin shift during puberty lasts until our 20s.

The “West End” effect.

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

This study found that West 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 some other cancers are higher at the western end of a time zone.

Scientists believe 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 time of daily work, school or sleep is based on the clock and not on the rising and setting of the sun.

A Brief History of Daylight Saving Time

Congress enacted daylight saving time during World War I and World War II and again during the energy crisis of the early 1970s.

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

Another argument in favor of summer daylight was that crime rates drop with more light at the end of the day. While this has been shown to be true, the change is very small and the health effects seem to outweigh the benefits to society from lower crime rates.

After World War II, setting the start and end dates for daylight saving time fell to state governments. Because this created many scheduling and railroad safety problems, however, Congress passed the Uniform Time Act in 1966. This law set the national daylight saving time dates from the last Sunday in April to the last Sunday in October. In 2007, Congress amended 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 opt out of daylight saving time. Arizona and Hawaii are on permanent standard time, along with Puerto Rico, the US Virgin Islands, the Northern Mariana Islands, Guam and American Samoa.

Now, many other states are considering whether to stop falling behind and get ahead. Several US states have pending legislation and resolutions in support of permanent daylight saving time, while many others have or are considering permanent daylight saving time. Legislation and resolutions for permanent standard time have increased from 15% in 2021 to 31% in 2023.

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

The uptick in activity among states seeking to escape these biannual changes reflects how more people are recognizing the downsides of the practice. Now, it’s up to lawmakers to decide whether to end the time shift entirely and opt for permanent daylight saving time.

This article was originally published on The Conversation. Read the original article.

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