Changing your clock twice a year is something you probably do without too much thought. But have you ever considered the impact of shifting the clock on your health?
Your body’s natural circadian rhythm impacts your sleep-wake cycle and many other bodily processes. And when this internal clock gets disrupted during the “fall back” or “spring forward,” there are various health consequences.
On March 15, 2002, you may have noticed that the US Senate passed the Sunshine Protection Act to make daylight saving time (DST) permanent.¹
However, the bill has stalled, and sleep specialists suggest the initiative is misguided.
The American Academy of Sleep Medicine officially opposes it and recommends that permanent standard time would be healthiest for the public.²
So, for the time being, Americans will continue setting the clock back an hour this fall. Compared to the previous day, the sun will rise and set an hour earlier.
Here’s some background on how daylight versus standard time affects you and why “ditching the switch” has yet to be signed into law.
Many countries across the globe advance the time in the summer months –– typically shifting their clocks forward an hour from standard time.
Usually, the clocks move one hour forward in the springtime to have the sun shine an hour later –– creating longer summer days –– and then it gets moved back to standard time in the fall.
The result is less sun exposure in the morning and more in the evening.
Hence, the common expression is “spring forward and fall back.”
In the US, most states shift between standard time and daylight saving (DST) time annually.
In 2022, DST commenced on Sunday, March 13, and will end on Sunday, November 6, 2022.
However, over 60% of the world’s countries do not switch their clocks, often for convenience and health reasons.³
(In countries closer to the equator, there’s no benefit to switching the clocks because they receive more average hours of sunlight than, say, in North America).
Although changing our clocks is something most of us are used to, some research suggests that most Americans would prefer to stop changing the time twice a year.
A poll by Associated Press-NORC Center for Public Affairs Research in October 2019 found that 71% of Americans prefer to do away with time changes.⁴ Only 28% of those surveyed wanted to continue changing their clocks.
For those who preferred not to change time, 40% would like year-round standard time, while 31% would like year-round DST.
Everyday Americans aren’t alone in wishing for an end to DST — many health organizations agree.
The National Sleep Foundation says it would be healthier and safer for Americans to ditch DST:
“The human circadian system does not adjust to annual clock changes. Sleep becomes disrupted, less efficient, and shortened. DST forces our biological clocks out of sync with the sun's rising and setting (the sun clock). The link between our biological clock and the sun clock has been crucial to human health and well-being for millennia,” says an official statement.⁵
In agreement, the American Academy of Sleep Medicine suggests that DST can cause circadian misalignment and advises that “seasonal time changes should be abolished in favor of a fixed, national, year-round standard time.”⁶
Having first come into practice in 1918, DST took hold in most US states by the 1960s.⁷
In 1973, DST was widely adopted as an effort to reduce oil demand during an energy crisis.
An extra hour of daylight in the evening was found to be helpful for businesses, as people continued to shop, watch sports, and engage in other economic activities.⁸
However, clock changes may become a thing of the past.
The Sunshine Protection Act of 2021 is intended to begin on November 5, 2023, but it’s still being determined whether lawmakers will push the change forward.¹
The legislation will purportedly help citizens enjoy longer afternoons while reducing seasonal depression and other ill effects — but evidence suggests it may not be as beneficial as hoped.
Your body has a natural circadian rhythm. This rhythm manages many critical functions including your blood pressure, moods, and body temperature, among other things.
Circadian rhythm can even impact how much you eat at different times of the day.
Circadian rhythm is also an internal clock because it regulates the sleep-wake cycle across 24 hours.
That means the circadian rhythm regulates the time you go to sleep at night and when you wake in the morning.
Your natural circadian rhythm links to sunlight exposure –– it’s impacted by the amount of bright light exposure you experience in the day, and when you stop receiving natural light in the evening.
When you change the clocks, there is a resulting internal effect. It can cause you to become out of sync with the natural sun rising and sunset.
Some people may feel tired in the morning while feeling more awake at night and lead to a lack of sleep.⁹
For example, a 2019 survey found that 55% of respondents felt “extremely” or “somewhat tired” after the move to DST.¹⁰
The effect was more pronounced in those identifying as women (62%) versus those identifying as men (49%).
The twice-yearly shift correlates with more than a little bit of lost sleep.
Serious adverse events are more likely to occur during time switches.
During the days and weeks of daylight time changes, there is an increased risk of cardiovascular events, acute atrial fibrillation, and emergency room visits.¹¹
A 2020 study found that DST increases negative health effects –– an estimated 150,000 incidences in the US and 880,000 globally.¹²
Researchers in Sweden found that the number of heart attacks increased by roughly 5% during the first week of DST.¹³
Both moving into and out of DST has been linked with sleep issues, mood disturbances, and even suicide. There’s also an increase in the number of car crashes during the days around clock switches, with 6% more fatal traffic accidents occurring than usual.¹³
In the Journal of Clinical Sleep Medicine, experts from the American Academy of Sleep Medicine discuss the resulting sleep debt:¹³
“The end result is a variety of cellular derangements, including altered myocyte gene expression, altered epigenetic and transcriptional profile of core clock genes, increased production of inflammatory markers, lower vagal tone resulting in higher heart rate and blood pressure, and reduced sleep.”
While negative effects are most strongly linked to switching from standard time to DST, moving the clocks backward an hour can increase mood imbalances too.
Losing sunlight in the afternoon –– once the clocks return to standard time in the fall –– can cause increases in several mental illnesses, including seasonal affective disorder.
For example, a study in Denmark found an 11% increase in depression after the return to standard time.¹⁴
The effects can be more pronounced for those who live further from the equator and therefore experience shorter winter days. Researchers were clear that the depression occurred due to the change in time, not just the natural changing of the seasons:
"We are relatively certain that it is the transition from daylight saving time to standard time that causes the increase in the number of depression diagnoses and not, for example, the change in the length of the day or bad weather. In fact, we take these phenomena into account in our analyses," said Søren D. Østergaard, Associate Professor Søren D. Østergaard from Aarhus University Hospital.
In addition, an Australian study found that the minor time changes associated with daylight saving led to an increase in male suicide rates in the weeks after the changes occurred.¹⁵
Though you can’t control whether the region you live in adopts daylight saving time, you do have some control over how it impacts your body.
There are several ways to lessen the effects of time changes.
Gradually transitioning bedtime Going to bed 15-20 minutes earlier in the night leading up to daylight saving changes, minimizes the effects on your body and sleep.
Gradually transitioning other activities You can use the same technique with other daily activities, like the time you rise, and the times at which you eat, to subtly help your body to adjust gently to the changed time.
Walk in sunlight first thing in the morning Exposure to sunlight is critical for your circadian rhythm. Getting sunlight first thing helps signal to your body that it’s time to wake up, which can help make the transition easier.
Avoid devices at night Exposure to bright devices can throw your internal clock off. Dimming your devices or avoiding them altogether before bedtime is helpful to allow your body to wind down and expect sleep.
Help children to adjust Children need significantly more sleep than adults. According to the Sleep Foundation, school-age children require between 9 and 11 hours of sleep daily. Younger children, between three and five years old, need 10–13 hours of sleep. It may be helpful to put them to bed around ten minutes earlier the week before the clocks change. That way, once the clocks are updated, they’ll be more likely to be fully adjusted.
While changing your clocks twice a year might be something you’re accustomed to, it could impact your health more than you realize. However, there are many ways to mitigate the effects of daylight savings time, such as gradually changing the time you go to bed, walking in sunlight early in the morning, and removing devices from the bedroom for a more restful sleep.
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S.623 - Sunshine protection act of 2021 | Congress.gov
What is standard time? | timeanddate
Daylight saving time vs standard time | The Associated Press and NORC
Survey: 55% of US adults feel tired after spring daylight saving time transition | American Academy of Sleep Medicine
Chloe Garnham is a writer exploring a broad range of topics, including healthcare, education, and technology.