Why daylight saving time may be bad for your brain and health

by UT Southwestern Medical Center

edited by Swati Mestri, reviewed by Andrew Zinin

Swati Mestri

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Turning the clocks back an hour each fall can feel like a gift: an extra hour of sleep. But the trade-off is less daylight in the evening, and the annual switch continues to earn mixed reviews. The same is true in spring, when we lose an hour as daylight saving time begins.

But this twice-a-year reset isn't so easy for our internal clocks—also known as our circadian rhythms. In fact, desynchronization of our body clocks has been linked to increased risks of depression, obesity, heart attack, cancer and even car accidents.

In 1997, my laboratory discovered the CLOCK gene—the first circadian gene in mammals. My colleagues and I determined that mutated CLOCK genes can cause delays in circadian functions, which in turn lead to dysfunctions in metabolic, behavioral and cognitive abilities.

Every cell in our bodies keeps track of the time, and changes in daily patterns can trigger stress in our brains and cause sleep deprivation, disorientation and memory loss. These changes can also lead to difficulties with learning, social interactions and overall cognitive function.

In 2016, in collaboration with Dr. Masashi Yanagisawa's laboratory, we used an unbiased mutagenesis and screening method to discover the first genes in mice that regulate sleep. We uncovered two genes in mice that control how much rapid eye movement (REM) sleep and non-REM sleep are needed. A healthy sleep pattern should include long stretches of non-REM sleep, when the brain is not actively dreaming and processing memories.

With this knowledge, we can begin to understand why sleep is important for our health and how to improve sleep hygiene for the 15% to 20% of people in the U.S. with sleep disorders—particularly when environmental factors disrupt our health.

While there is still a lot of uncharted territory in the field of circadian rhythms and sleep medicine, there is a growing body of evidence to suggest that springing forward and falling back is not the best choice for the 21st century.

How daylight saving time can disrupt our health

Sleeplessness is commonly associated with stress, and the last six years have been among the most stress-filled years in recent memory. It's likely that more people were struggling with sleep deprivation than was reported during the COVID-19 pandemic. Having to readjust once again is bound to be another hurdle for people in the U.S.

Add this to these facts—26% fewer third-shift workers than first-shift workers report getting enough sleep, and teens and tots typically get far less than their recommended 10 hours nightly due to demanding school, sports and social schedules—and daylight saving time seems to be exacerbating an already prevalent issue.

Low mood and depression

Sleep disruptions can also increase the risk of mental illness. In the fall, losing an hour of evening light can markedly affect our mood—and signal the beginning of seasonal affective disorder, a type of depression that is associated with a lack of sunlight.

Darkness = sleepy + grumpy

Darkness promotes the production of melatonin, a hormone that helps signal to the body that it is time to sleep, while light suppresses it. Sunlight also influences serotonin activity, which plays an important role in regulating mood. As daylight hours shorten, changes in light exposure can affect both mood and sleep patterns.

One study showed that hospitals reported addressing 11% more depressive symptoms right after the fall time change. The time change in the spring did not produce a similar result, supporting the notion that sunlight does our minds and bodies good.

Cardiovascular risks

Multiple studies have shown a small increase in heart attacks after the start of daylight saving time in the spring and a small decrease at its end in the fall. Meanwhile, stroke rates are 8% higher in the first two days following both time changes.

Vehicular crashes

Fatal traffic accidents also become more of a danger after the spring time change. A study showed that fatal accidents increase 6% and are more common in the mornings directly after the clock change. There did not appear to be an effect from the fall-back transition to standard time.

Of course, one season of time changes is highly unlikely to cause issues. However, over time, we must be mindful of how sleep, or lack thereof, affects our overall health. While we can't manually reset our internal clocks, try these tips to have a more restful daylight saving time transition this year.

Tips to manage daylight saving time transitions

1. Make a gradual shift

A few days before the fall time change, start going to bed and waking up 10 to 15 minutes later each day to help your body gradually adjust. Before the spring time change, shift your bedtime and wake-up time 10 to 15 minutes earlier each day instead.

2. Stick to your sleep schedule

Once the clock changes, try to keep things as normal as possible. Get up and go to bed at your normal times. The same goes for your other daily routines, such as eating and exercising.

3. Maintain good sleep hygiene

A healthy bedtime routine can do wonders for your sleep. A few good sleep hygiene habits to follow include going to bed and waking up at the same time every day; not watching TV or browsing social media; avoiding caffeine and alcohol in the evening; and not exercising before going to bed.

4. Get out in the sun

Spending time outdoors during daylight hours, even if it's only for a quick walk over lunch, can help stimulate your body. You also can sit by a window or try light therapy.

5. Limit your caffeine intake

You don't have to skip your morning cup of coffee, but try not to go overboard if you hit an afternoon slump. And stay away from caffeinated beverages in the evening so you can fall asleep when you should and stay asleep.

Keeping your circadian rhythms in sync

The fall time change, when you gain an hour of sleep, is thought to be an easier adjustment than "springing forward" in March, but many scientists believe any disruption of the optimal phasing of our circadian rhythms—the timing of our rhythms relative to the phase of the solar day-night cycle—can be a culprit in associated health risks.

Organized efforts to "lock the clock" and "ditch the switch" have gained traction in recent years. But daylight saving time remains a fixture in about 70 countries, including the U.S., where it was first introduced in 1918 and later formalized by the Uniform Time Act of 1966.

For now, there are no large-scale changes on the horizon, so we must "spring forward" and "fall back" to the best of our abilities. Understanding that daylight saving time disrupts our circadian rhythms is a start. And knowing that help is available for sleep deprivation or disorders is the key to coping with the condition.

Key medical concepts

Circadian RhythmSleep DeprivationSeasonal Affective DisorderMyocardial infarctionStroke

Clinical categories

Sleep medicineSleep & RecoveryCommon illnesses & PreventionPsychology & Mental health Provided by UT Southwestern Medical Center Who's behind this story?

Swati Mestri

Swati Mestri holds a bachelor's degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space. Full profile →

Andrew Zinin

Master's in physics with research experience. Long-time science news enthusiast. Plays key role in Science X's editorial success. Full profile →

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