The following essay is reprinted with permission from The Conversation, an online publication about the latest research.
As the people of the United States prepare to put their clocks forward one hour on Sunday, March 12, 2023, I prepare for the annual ritual of media coverage of the disruptions to daily routines caused by the change from standard time to caused by daylight saving time.
About a third of Americans say they don’t look forward to these twice-yearly time changes. And nearly two-thirds would like to eliminate it entirely, compared to 21% who are unsure and 16% who would like to turn their clocks back and forth.
But the impact goes beyond simple inconveniences. Researchers are discovering that each March’s “jumping forward” is linked to serious negative health effects, including a rise in heart attacks and sleep deprivation among teenagers. In contrast, the fall transition back to normal is not associated with these health effects, my co-authors and I noted in a 2020 comment.
As a professor of neurology and pediatrics and director of the sleep department at Vanderbilt University Medical Center, I studied the ins and outs of these biannual rituals for over five years. It has become clear to me and many of my colleagues that the switch to daylight saving time affects health every spring immediately after the clock change and also for the nearly eight months that Americans observe daylight saving time.
The strong plea for permanent normal time
Americans disagree on whether they prefer permanent Daylight Saving Time or permanent Standard Time.
However, the two time shifts – jerky as they may be – are not the same. Standard time is closest to natural light, with the sun directly overhead at or around midday. In summer time from March to November, on the other hand, the time change resulting from summer time means that natural light is available one hour later in the morning and one hour later in the evening, depending on the time.
Morning light is important for setting the body’s natural rhythm: it wakes us up and improves alertness. Morning light also lifts mood – light boxes 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 light’s effects on increasing levels of cortisol, a hormone that modulates the stress response, or light’s effect on the amygdala, part of the amygdala of the brain involved in emotions.
Teens can also be chronically sleep deprived due to school, sports, and social activities. For example, many children start school around 8 a.m. or earlier. This means that many young people get up and go to school in the dark during the summertime.
The evidence supports the adoption of a permanent standard time across the country, as I testified at a congressional hearing in March 2022 and argued in a recent statement for the Sleep Research Society. The American Medical Association recently called for a permanent standard time. And in late 2022, Mexico introduced permanent standard time, citing health, productivity and energy savings benefits.
The biggest benefit of DST is that it provides an extra hour of light for exercising, shopping, or dining al fresco in the late afternoon or evening, depending on the time of year. However, late-evening light exposure for nearly eight months during daylight saving time comes at a price. This prolonged evening light delays the brain’s release of melatonin, the hormone that promotes sleepiness, which in turn disrupts sleep and causes us to sleep less overall.
Because puberty also causes melatonin to be released later in the night, and as a result, teenagers have delayed the natural signal that helps them fall asleep, adolescents are particularly vulnerable to disrupted sleep from the prolonged evening light. This shift in melatonin during puberty continues well 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 on the western edge of a time zone, with later morning and evening light, got less sleep than their counterparts on the eastern edge of a time zone.
This study found that Western Rim residents had higher rates of obesity, diabetes, heart disease, and breast cancer, as well as lower per capita income and higher healthcare costs. Other research has found that rates of certain other types of cancer are higher at the western edge 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 temporal discrepancy 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, not sunrise and sunset.
A Brief History of Daylight Saving Time
Congress instituted year-round daylight saving time during World Wars I and II, and again during the energy crisis of the early 1970s.
The idea was that additional light later in the afternoon would save energy by reducing the need for electric lighting. This idea has since proved largely inaccurate, as winter heating demands can increase in the mornings, while summer air conditioning demands can also increase in the late afternoon.
Another argument for DST was that crime rates go down with more light at the end of the day. While this has proven to be true, the change is very small and the health effects appear 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 the state governments. However, because this created many railroad planning and safety problems, Congress passed the Uniform Time Act in 1966. This law fixed the nationwide dates of 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 observed from the second Sunday in March to the first Sunday in November – dates that are still valid today.
However, the Uniform Time Act allows states and territories to opt out of 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 stop falling behind and jump forward. Several US states are considering legislation and resolutions to support permanent standard time, while many others have or are considering permanent daylight saving time. Perpetual Standard Time laws and enactments have increased from 15% in 2021 to 31% in 2023.
In March 2022, the US Senate passed the Sunshine Protection Act to make daylight saving time permanent. But the House made no progress with this legislation. Florida Senator Marco Rubio reinstated the law on March 1, 2023.
The surge in activity among states trying to deviate from these twice-yearly changes reflects more people realizing the downsides of the practice. It is now up to the legislature to decide whether we will end the time difference entirely and opt for permanent winter or summer time.
This article was originally published on The Conversation. Read the original article.