An hour might not seem like much time. But when daylight saving time begins in the spring or ends in the fall, even that small shift can affect how well you sleep, how alert you feel, and how your body functions.
Regardless of which way the clock ticks, experts have long argued that the one hour adjustment is hard on our bodies, as the shift temporarily throws our circadian rhythms out of sync, changing our sleep patterns, and how you feel. Bottom line: One hour barely registers on the clock, but your body may disagree. Here’s what’s going on.
Your sleep takes the first hit
Daylight saving time and sleep share an intimate connection. When daylight saving time (DST) starts in March, clocks spring forward, and you lose an hour of sleep for one day. That may not sound like a big deal—you may have weekend nights where you go to bed late anyway, but these clock effects linger. It’s one reason why the American Academy of Sleep Medicine (AASM) published a position statement in 2020 calling for an end to DST in favor of a fixed, year-round standard time in the U.S.
To understand the connection between circadian rhythm and daylight saving time, it helps to look at how your body responds to natural light. Light helps regulate your internal clock, signaling when it's time to wake up and when it's time to sleep. When clocks move forward in the spring, you get less morning light and more evening light. This can temporarily throw your internal clock out of sync with your daily schedule, making it harder to fall asleep, stay asleep, or feel rested.
As a result, you may feel more tired, irritable, distracted, or just generally “off” in the days following the transition.
Research suggests that springing into daylight saving time is more harmful to sleep quality than in autumn when clocks correct back to standard time (ST). Going back to standard time doesn’t fully undo what happens in the spring, though, and some people will then struggle with waking up early in the morning and feeling less alert in the evening.
Related: The top 5 proactive health habits our doctors rely on all year long
Your hormones follow a clock, too
What’s interesting is how sleep-related hormones change (or don’t) when the clocks shift. Research suggests that cortisol—known as your “stress hormone”—is impacted, but it also helps give you the get-up-and-go you need in the morning. Sunrise is the most impactful cue for cortisol and your body’s cortisol timing doesn’t shift just because society changed the clocks.
Then, there’s melatonin. Melatonin is a natural hormone your body produces to regulate your sleep. Melatonin rises before bed, signaling your body that it’s getting ready for sleep. When you set your clock back, this melatonin rise will occur around dinnertime until you adjust, according to Mass General Brigham. While your sleep adjusts based on daylight and your schedule, some people are more sensitive to these changes, including hormonal disruption. It’s recognized that there are short-term increases in mental health symptoms like depression, anxiety, and risk of suicide, and is especially dangerous if you have a preexisting psychological condition.
Sleep is one of several factors that can influence your health over time. And while there’s no reason to do lab testing to assess your hormones specifically due to daylight saving time, lab work can provide information about certain hormones and biomarkers for an overall view of your physiological systems.
Related: Is nervous system regulation a new longevity metric?
It may affect more than your energy
Daylight saving time is not just an hour here or there, it’s a temporary transition that has wide-ranging effects and possible significant implications for some people. For example, switching to DST has been associated with an increase in heart attacks and strokes during the two days after the transition. Although it remains a mystery why, experts think that it’s the effect on the circadian rhythm that boosts this risk. That’s also the proposed theory as to why the time change—especially DST—is associated with a slight increase in obesity prevalence, notes research in the Proceedings of the National Academy of Sciences, USA.
Fatigue from that hour lost has also been linked to an increase in fatal traffic accidents, with researchers predicting that about 28 fatal accidents may be eliminated every year if we did away with DST. And the fall transition presents a different concern—with sunset occurring earlier, more evening commuters are on the road after dark, when deer and other wildlife are often active. Research suggests this overlap may contribute to an increased risk of wildlife-vehicle collisions.
In new Prenuvo research that examined sleep duration and sleep efficacy alongside MRI-based brain and visceral fat measurements in 14,031 adults, the study found that sleep duration and efficiency were associated with different brain and metabolic imaging biomarkers, including parietal gray matter volume, hippocampal volume, and visceral adipose tissue. It shows that sleep and brain health are connected well beyond energy and alertness.
Related: How your brain changes with age
While any clock change may have temporary effects, ongoing sleep problems are a separate health issue that deserves its own medical workup and investigation. Poor sleep is one of the many factors that can influence health over time, alongside diet, exercise, stress, environmental factors, and more.
How to make the transition easier
Some sources suggest you can make the transition in the fall or spring easier on your body by leveraging light manipulation. Here’s what you can do:
- Get outside and take a morning walk for a half hour after the spring clock change, and likewise, go for an evening walk after the fall change.
- Wear sunglasses for two hours in the morning for the first four mornings after the autumn time change.
- Reduce your light exposure in the evening in the spring and increase it in the fall.
In addition, when it comes to daylight saving time and circadian rhythm, prioritize adequate sleep around the transition. Consider gradually adjusting your sleep and wake times before the clock change, if possible. The AASM recommends going to bed 15 to 20 minutes earlier each night before a time change. If you feel drowsy in the morning after the spring time change, be careful while driving. Stick to your usual bedtime so you can get the sleep you need.
Related: The top 5 proactive health habits our doctors rely on all year long
Think beyond the clock change
The effects of a one-hour time change are generally temporary, but they offer a reminder of how closely sleep is connected to other aspects of your health. And while adjusting your sleep schedule can help you navigate the transition, understanding your health over time involves looking at more than your nightly rest.
For those interested in a proactive approach to health, assessments such as bloodwork, Body Composition Analysis, and whole body MRI can provide different types of information. Bloodwork can measure certain biomarkers related to metabolic health, body composition measurements can quantify visceral fat and muscle, and MRI can help identify structural findings across 65 organs.
These assessments can't determine whether a particular finding was caused by your sleep habits or a change in the clocks. However, they can offer valuable insights into your health that you can discuss with your doctor.
To learn more about how Prenuvo could fit into your approach to proactive health, book a call with our Patient Services Team.
