The Hidden Cost of Daylight Saving Time — Why One Hour Changes Everything
It‘s just one hour. What could possibly go wrong?
Every spring, more than 70 countries around the world move their clocks forward by one hour. Every fall, they move them back. The biannual ritual has become so routine that most people barely think about it — except for the groggy Monday morning after the spring transition.
But that one hour is not trivial. It is not just about losing sleep. It is about circadian rhythm disruption — a misalignment between your body‘s internal clock and the external world that affects everything from your heart to your mood to your risk of being in a car accident.
The evidence from recent research is clear: daylight saving time is not neutral. It is a public health event.
1. What Happens to Your Body When the Clocks Change
(1) The Circadian Rhythm Disruption
Your body runs on an internal clock — a circadian rhythm that cycles approximately every 24 hours, regulating everything from hormone secretion to body temperature to sleep-wake cycles. This clock is synchronized primarily by light exposure: morning light advances it, evening light delays it.
When you abruptly shift your clocks by one hour, you are not just changing the time on your wall. You are changing the timing of light exposure relative to your internal biology. This creates a state of circadian misalignment — a “social jet lag” that can take several days to resolve.
Every cell in your body keeps track of time. When daily patterns change abruptly, it triggers stress in your brain and can cause sleep deprivation, disorientation, and memory loss.
(2) The Spring Transition Is Worse
Not all clock changes are equal. The spring transition — when we lose an hour of sleep — is consistently associated with more severe effects than the fall transition.
A 2025 systematic review published in Sleep Medicine Reviews analyzed 27 studies on the effects of daylight saving time on sleep and sleepiness. The review found that the transition to DST was associated with adverse effects on sleep duration and quality, as well as increased sleepiness — effects that were more evident in evening chronotypes (people who naturally prefer later bedtimes).
2. The Cardiovascular Toll — Heart Attacks and Strokes
(1) The 24% Increase in Heart Attacks
The cardiovascular effects of the spring time change are among the most well-documented. According to the American Heart Association, scientific researchers have noticed a marked increase in heart attacks and strokes in the days following the spring transition.
A study of hospital admissions across Michigan found a 24% increase in heart attacks on the Monday following the switch to daylight saving time. The Monday after the time change is particularly concerning because, in general, more serious heart attacks already occur on Mondays than any other day of the week.
(2) The 8% Increase in Strokes
The stroke risk is equally concerning. A study from Finland found that the overall rate of ischemic stroke was 8% higher during the first two days after a daylight saving time transition.
(3) The Long-Term Picture
The effects are not just immediate. A 2025 study by Stanford Medicine researchers modeled how different time policies would affect people‘s circadian rhythms and health. The team found that either permanent standard time or permanent daylight saving time would be healthier than biannual switching. Permanent standard time would result in an estimated 300,000 fewer strokes and 2.6 million fewer people with obesity.
“We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year,” said Jamie Zeitzer, PhD, professor of psychiatry and behavioral sciences at Stanford and senior author of the study.
3. The Safety Crisis — Traffic Accidents
The spring time change does not just affect your health. It affects your safety.
(1) Fatal Crashes Increase by 12%
A 2025 study published in the Journal of Safety Research examined fatal crashes in the contiguous United States from 2010 to 2019 in the five weeks before and after biannual time changes. The findings were striking:
- Motor-vehicle occupant fatal crashes increased by 12% in the five weeks after the springtime change
- Motor-vehicle occupant fatal crashes decreased by 7.1% after the fall time change
- Overall, time changes resulted in a net increase of 29 motor-vehicle occupant crashes
(2) The 6% Increase in Fatal Car Accident Risk
Other research has found a 6% increase in fatal car accident risk in the days following the start of daylight saving time. A ten-year analysis found that fatal crashes in the week after DST increased by 25.9% compared to the week before.
(3) Why Does This Happen?
The increase in crashes is driven by two factors:
- Sleep disruption — impaired cognitive capacity from the lost hour of sleep
- Changing light conditions — reduced visibility and driver fatigue
A study from Chile found that sleep disruption increases automobile accidents by 6% in the first week following the transition into DST. The reallocation of light also plays a role: the spring switch results in darker mornings, when drivers are commuting.
4. The Mental Health Toll
(1) Depression, Anxiety, and Sleep Disruption
The mental health effects of clock changes are increasingly well documented. A comprehensive review published in 2025 found that DST — particularly spring forward transitions — is associated with:
- Increased sleep disturbance
- Impaired executive functioning
- Reduced attention and working memory
- Heightened emotional reactivity
- Increased depressive symptoms
- Elevated risk of manic episodes
- Short-term increases in suicidality
(2) The Autumn Effect
The fall transition has its own effects. A 2025 population-based cohort study in England found that in the week after the autumn clock change, there was a 3% reduction in recorded anxiety diagnoses and reductions in depression, sleep disorders, and psychiatric presentations. The researchers concluded that “the week after the autumn clock change was associated with a reduction in events for cardiovascular disease, sleep disorders, and mental health disorders.”
However, the loss of evening light in the fall can also trigger seasonal affective disorder, a type of depression associated with reduced sunlight exposure.
(3) The Vicious Cycle
The relationship between daylight saving time and mental health is bidirectional. Sleep disruption caused by the time change worsens mood, and worsened mood makes it harder to sleep. This vicious cycle can persist for days or even weeks after the transition.
5. The Debate — Permanent Standard Time vs. Permanent DST
(1) The Case for Permanent Standard Time
Organizations such as the American Academy of Sleep Medicine, the National Sleep Foundation, and the American Medical Association have endorsed year-round standard time.
Why? Because morning light is essential for health. Standard time aligns more closely with the natural light-dark cycle, allowing morning light to properly entrain the circadian rhythm. Permanent standard time would result in an estimated 300,000 fewer strokes and 2.6 million fewer cases of obesity.
(2) The Case for Permanent DST
Proponents of permanent daylight saving time argue that more evening light could save energy, deter crime, and give people more leisure time after work. However, a trial of permanent DST begun in 1974 was so unpopular that it was abandoned after less than a year, with parents particularly concerned about children going to school in the dark.
(3) The Consensus
The Stanford Medicine study found that either permanent standard time or permanent daylight saving time is better than switching twice a year. But permanent standard time benefits the most people.
“We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year,” Zeitzer said.
6. What You Can Do — Evidence-Based Strategies
(1) Start Adjusting Early
The CDC recommends starting to adjust your sleep schedule several days before the time change. Go to bed 15–20 minutes earlier each night in the days leading up to the spring transition.
(2) Get Morning Light
Morning light is the most powerful way to reset your circadian rhythm. Get outside and get as much natural light as possible each day, especially in the morning.
(3) Wind Down Earlier
Begin winding down a little earlier in the evenings ahead of the time change. While you can never make up lost sleep, going into the time change well-rested can help.
(4) Limit Caffeine
It may be tempting to reach for extra coffee, but too much caffeine is not heart-healthy and can further disrupt sleep.
(5) Prioritize Sleep Hygiene
Maintain a consistent sleep schedule, keep your bedroom cool and dark, and avoid screens before bed. A comfortable, predictable sleep environment supports your body‘s natural ability to adapt.
7. The Role of Environment — Supporting Your Sleep Through the Transition
Here is what we believe at Moihug: your environment shapes your rest. Not by curing anything, but by removing friction — physical friction, sensory friction, environmental friction — so your body can do what it already knows how to do.
The Moihug Deep Sleep Pillow is not a treatment for sleep disorders, circadian disruption, or any medical condition. It is a long plush body pillow — an environmental comfort tool that can help you settle into restful sleep, even when your internal clock is out of sync.
What it offers:
- Gentle, automatic patting — slow, rhythmic tactile input that may help calm an active nervous system as you wind down
- Wireless audio — stream white noise, guided relaxation, or bedtime stories through the pillow to create a consistent, calming pre‑sleep environment
- Adjustable warmth — gentle heat up to approximately 110°F for added comfort
- Voice recording — record your own calming messages or positive affirmations
Think of it this way: your sleep environment sends signals to your brain about whether it is time to rest or time to stay alert. When your circadian rhythm is disrupted by a clock change, a predictable, comfortable environment can help bridge the gap.
👉 Create a more restful sleep environment, even when the clocks change. Explore the Moihug Deep Sleep Pillow here.
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Summary: One Hour Is Not Just One Hour
Every spring, we lose an hour of sleep. Every fall, we gain one back. The biannual ritual has become so routine that we barely notice it — except for the groggy Monday, the sluggish week, the vague sense that something is off.
But the evidence from 2024 and 2025 is clear. The spring transition to daylight saving time is associated with a 24% increase in heart attacks, an 8% increase in strokes, a 12% increase in fatal car crashes, and significant mental health effects including increased depression, anxiety, and suicidality.
The fall transition brings its own challenges, including the loss of evening light that can trigger seasonal affective disorder.
The solution is not complicated. Either permanent standard time or permanent daylight saving time would be healthier than biannual switching. But permanent standard time — with its morning light — benefits the most people.
Until the policy changes, protect yourself. Start adjusting early. Get morning light. Wind down earlier. And create a sleep environment that supports your body‘s natural ability to rest.
Your body knows how to sleep. It always has. Your job is not to force it. Your job is to create the conditions — the consistent schedule, the calming routine, the comfortable environment — that let it do what it already knows how to do.
Start with one change today. Not everything. Just one.
References
- Romigi A, et al. The effects of daylight saving time and clock time transitions on sleep and sleepiness: a systematic review. Sleep Medicine Reviews. 2025;84:102161.
- Weed L, Zeitzer J, et al. Modeling the health impacts of permanent standard time, permanent daylight saving time, and biannual switching. Proceedings of the National Academy of Sciences. 2025.
- American Heart Association. Here‘s your wake-up call: Daylight saving time may impact your heart health. 2026.
- Sandhu A, et al. Daylight saving time and fatal crashes: The impact of changing light conditions. Journal of Safety Research. 2025;93:200-205.
- Gillmore R. Daylight Saving Time and Automobile Accidents: Evidence From Chile. Health Economics. 2025;34(5):880-931.
- When the Clock Shifts: A Comprehensive Review of Daylight-Saving Time (DST), Circadian Disruption, and Neuropsychological Risk in Chronic Mental Illness. PubMed. 2025.
- De Lange, et al. Acute effects of daylight saving time clock changes on mental and physical health in England: population based retrospective cohort study. BMJ. 2025.
- UT Southwestern Medical Center. Why daylight saving time may be bad for your brain and health. 2025.
- Boston University School of Public Health. The Clouded Harms of Clock Changes. 2025.