Why Your Body Wants Standard Time
- Standard time aligns human circadian biology with natural light, while daylight saving time creates chronic circadian misalignment that harms sleep, health, and cognitive performance.
- Daylight saving time disrupts the body’s circadian system by delaying morning light and extending evening light, leading to sleep deprivation, reduced productivity, and increased health risks. Research consistently shows higher rates of accidents, heart attacks, and long-term metabolic and cardiovascular disease during DST. Permanent standard time best supports human biology, workplace performance, and public health.
- Written by Ginny Estupinian, PhD, ABPP Board-Certified Clinical Psychologist
Licensed Psychologist, California
Practice: Ginny Estupinian PhD
Location: Los Gatos, California
Specializing in sleep regulation, circadian health, stress, and cognitive performance using evidence-based psychological science.
In this article, you will learn:
- How the circadian system regulates sleep, alertness, and performance
- Why daylight saving time creates circadian misalignment
- The role of morning light in productivity and emotional regulation
- How extended evening light interferes with melatonin and sleep quality
- The short-term health risks linked to DST transitions
- The long-term health consequences of chronic circadian disruption
- Why adolescents and young adults are disproportionately affected
- How DST reduces workplace performance and increases accidents
- Why permanent standard time is supported by medical organizations
- The key differences between permanent standard time and permanent DST
Recently, while speaking about productivity, I mentioned that daylight saving time affects workplace performance and that, as managers, we needed to keep this in mind as we approach another time change. A perplexed audience member asked, “Weren’t we getting rid of this practice?”
Sadly, no. Daylight Saving Time will begin again on Sunday, March 9, 2025, at 2:00 AM local time. This is happening despite nearly two-thirds of Americans wanting to eliminate these time changes, and only 16% preferring the current system. The reason people don’t like these time changes goes far beyond inconvenience. Research shows these twice-yearly shifts undermine workplace performance and public health in profound ways.
The Science: Why Time Changes Hurt Us
Our circadian system is an internal biological clock regulating sleep, alertness, decision-making, and cognitive performance. This system synchronizes with environmental light cues to maintain coordination among organ systems. Standard time aligns closely with these natural biological rhythms, with the sun directly overhead near noon. During DST, however, the clock artificially shifts natural light by 1 hour, creating “circadian misalignment,” a mismatch between our biology and the outside world.
Morning light is essential for productivity. When sunlight enters our eyes in the morning, it triggers cortisol release (promoting wakefulness and mental clarity) and activates the amygdala (regulating emotions). This is so powerful that light boxes simulating natural sunlight are prescribed to treat seasonal affective disorder.
Evening light causes problems. Extended evening light during DST delays melatonin release, the hormone that promotes drowsiness. This doesn’t just push bedtime back slightly; it also interferes with sleep quality and reduces overall sleep time, leading to chronic sleep deprivation.
The Real Costs of DST
A groundbreaking study published in Proceedings of the National Academy of Sciences USA found that eliminating time shifts and adopting permanent standard time could lower obesity and stroke rates. Furthermore, research led by Beth Ann Malow at Vanderbilt University Medical Center showed that the spring shift to DST is associated with increased heart attacks and sleep deprivation, with impacts lasting the entire eight months we remain on DST.
Disrupted Sleep and Chronic Fatigue
The transition to DST creates a cascade of sleep disruption that can last weeks or persist throughout the eight-month period. Workers go to bed later due to delayed melatonin but still wake at the same time, resulting in chronic sleep debt.
For adolescents and young adults, the problem compounds. Puberty naturally delays melatonin release, a biological shift lasting into our twenties. Combined with DST’s evening light extension, this creates severe sleep deprivation among young workers and students already struggling with early start times.
Reduced Workplace Performance
As daylight saving time ends, you might begin to notice that both your focus and your team’s focus will diminish. In other words, the extra hour of ‘sleep’ actually tanks productivity, energy levels, and motivation.
Here is why. During DST, especially in winter months, many workers commute and start work in darkness, missing crucial morning light exposure. Their circadian systems never receive the synchronizing signal needed for optimal performance. The result: workers making decisions while their bodies remain biochemically primed for sleep, with impaired cognitive function and emotional regulation throughout the day.
The spring transition causes immediate productivity declines due to sleep deprivation and the abrupt shift. More significantly, the misalignment persists for eight months, with workers’ biological clocks remaining one hour behind artificial clock time, creating ongoing tension between biological readiness and workplace demands.
Increased Accidents and Health Crises
Research shows higher risks of car accidents following time changes, particularly the spring transition. Sleep disruption and circadian misalignment impair alertness, slow reaction times, and compromise decision-making. The same factors increase workplace safety risks, especially in industries that require precision or operate heavy machinery.
The spring transition is associated with a measurable spike in heart attacks and strokes. These cardiovascular events result from acute stress placed on the body. The abrupt sleep disruption, combined with circadian misalignment, triggers cardiac events in vulnerable individuals. Notably, the fall transition back to standard time shows no such effects, proving the problem is specifically the misalignment with natural light patterns.
Long-Term Health Impacts
The disruptions compound over time, leading to chronic health issues with massive impacts on workforce productivity and healthcare costs. Research on people living at the western edge of time zones, who experience patterns similar to permanent DST with later morning and evening light, has shown significantly higher rates of obesity, diabetes, heart disease, breast cancer, and certain other cancers. These western-edge residents also have lower per capita income and higher healthcare costs.
Scientists attribute these problems to chronic sleep deprivation and persistent circadian misalignment. When workers spend eight months annually operating out of sync with natural light, the cumulative effects on metabolism, cardiovascular health, and cellular function create long-term disease risks.
Why Standard Time Wins
Several major medical organizations, including the American Medical Association and the American Academy of Sleep Medicine, advocate for permanent standard time based on compelling scientific evidence.
Natural light alignment: Standard time most closely approximates natural light patterns. Our bodies evolved over millennia to synchronize with the sun’s natural progression. Daylight saving time forces our internal biology out of sync with the external environment for eight months each year.
Maximum morning light exposure: Under standard time, more people naturally receive crucial morning light, allowing circadian systems to sync properly. Under DST, many miss this morning light entirely, particularly in the winter months.
Minimized evening light problems: Standard time avoids the excessive evening light that delays melatonin release and creates chronic sleep deprivation.
Protection for vulnerable populations: Standard time particularly benefits adolescents and young adults whose natural melatonin delay already challenges their sleep. Avoiding DST’s evening light extension prevents exacerbating their already delayed sleep schedules.
Geographic equity: Standard time reduces health and economic disparities between the western and eastern edges of time zones by aligning time more closely with natural solar time.
Debunking DST Arguments
Energy savings: This claim has been largely disproven. While evening electric lighting needs may decrease, winter morning heating and late summer air conditioning needs increase.
Crime reduction: While crime rates drop slightly with more evening light, the change is minimal, and health experts agree that negative health effects far outweigh these benefits.
Therefore, the main advantage often cited for daylight saving time, the additional evening light for activities, comes at a significant cost. It disrupts normal sleep-wake cycles, reduces sleep quality, and causes chronic circadian misalignment that harms overall health and productivity.
The Path Forward
Recognition is growing. State legislation supporting permanent standard time increased from 15% in 2021 to 31% in 2023. In March 2022, the U.S. Senate passed the Sunshine Protection Act to make DST permanent, but the House didn’t advance it. Many sleep researchers argue this would be the wrong choice, keeping Americans in chronic circadian misalignment. On October 28, 2025, a bipartisan group of senators, led by Senator Rick Scott (R-Fla.), attempted to pass legislation by unanimous consent to make daylight saving time permanent nationwide, but it failed.
Mexico adopted permanent standard time in late 2022, citing benefits to health, productivity, and energy savings. Several U.S. states and territories already use it: Arizona, Hawaii, Puerto Rico, the U.S. Virgin Islands, Northern Mariana Islands, Guam, and American Samoa.
Final Thoughts
The evidence is mounting that twice-yearly time changes carry hidden costs not just in health outcomes like heart attacks and strokes, but in day-to-day workplace productivity and long-term workforce health. For businesses, adopting permanent standard time means a healthier, more alert, and more productive workforce, with benefits that compound year after year.
The next time you struggle through a foggy Monday after the time change, remember: it’s not just you. It’s your circadian system fighting an artificial shift that science increasingly suggests we should eliminate. The question is no longer whether we should stop changing our clocks; it’s whether policymakers will choose permanent standard time over permanent daylight saving time.
Frequently Asked Questions
Why does daylight saving time disrupt sleep?
Daylight saving time delays evening darkness and melatonin release, pushing sleep later while wake times remain fixed. This leads to chronic sleep deprivation and circadian misalignment.
What is circadian misalignment?
Circadian misalignment occurs when internal biological rhythms are out of sync with environmental light cues. DST creates this mismatch by artificially shifting clock time away from natural solar time.
Why is morning light so important for health and productivity?
Morning light triggers cortisol release, improves alertness, and synchronizes the circadian system. Without it, cognitive performance, mood regulation, and energy levels decline.
How does daylight saving time affect workplace performance?
DST increases fatigue, impairs decision-making, and reduces focus. Workers often operate while their bodies are still biologically primed for sleep, lowering productivity and safety.
Does daylight saving time increase health risks?
Yes. Research links DST, especially the spring transition, to higher rates of heart attacks, strokes, workplace injuries, and car accidents due to acute sleep loss and stress.
Why are adolescents and young adults more affected by DST?
Puberty naturally delays melatonin release. DST compounds this delay, creating severe sleep deprivation in teens and young adults with early school or work start times.
Is permanent daylight saving time healthier than changing clocks?
No. Permanent DST would lock in chronic circadian misalignment year-round. Medical and sleep organizations consistently recommend permanent standard time instead.
Why do medical organizations support permanent standard time?
Standard time best aligns with natural light patterns, maximizes morning light exposure, minimizes evening light disruption, and reduces long-term health risks.
Does DST really save energy?
Evidence shows energy savings are minimal or nonexistent. Increased morning heating and summer air conditioning often offset reduced evening lighting use.
Which regions already use permanent standard time?
Arizona, Hawaii, Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, and Northern Mariana Islands all use permanent standard time, as does Mexico since 2022.