Q&A: Sleep experts warn against harmful effects of daylight saving time
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On Saturday night, most of us in the U.S. will lose an hour of sleep as we switch to daylight saving time.
The American Academy of Sleep Medicine (AASM) on March 2 announced that it continues to oppose a permanent daylight saving time (DST) bill — the Sunshine Protection Act — which was reintroduced by U.S. Sen. Marco Rubio of Florida. Rep. Vern Buchanan, also of Florida, introduced a companion bill in the House of Representatives.
The AASM stated in a press release that it supports eliminating the twice yearly time changes and advocates for legislation that restores permanent standard time.
“It is time to stop changing our clocks in the spring and fall but making daylight saving time permanent is the wrong choice,” AASM President Jennifer Martin said in the release. “The science is clear: Restoring permanent, year-round standard time is the best option for our health and well-being.”
In light of this controversy, Healio spoke with five sleep experts about the effects of time change on our mental and physical health and how to adjust. The experts include:
- Raj Bhui, MD, DABFM (Sleep Medicine), CCFP, DABOM, DWSS, a clinical faculty member at the University of British Columbia and member of the AASM Public Safety Committee;
- Jocelyn Y. Cheng, MD, senior director of neuroscience clinical research for Eisai, who also serves on the AASM Public Safety Committee;
- Erin Flynn-Evans, PhD, MPH, co-founder of Baby Sleep Science and consultant to the AASM Public Safety Committee;
- Reeba Mathew, MD, FCCP, associate professor in pulmonary, critical care and sleep medicine at McGovern Medical School at UTHealth;
and - Andrew Spector, MD, FAASM, associate professor of neurology at Duke University School of Medicine.
Healio: This weekend we change the clocks for daylight saving time. What physical and mental repercussions are associated with the time change?
Bhui: Jumping ahead by 1 hour for DST is associated with many detrimental effects, and there are actually two effects to unpack: the changing of the clock and chronic exposure to DST.
Sleep is a fine balance between our internal neurobiological processes, external cues and socioeconomic obligations, and light is the most important zeitgeber, or cue, for our internal circadian clock. Bright light exposure in the morning helps keep our internal circadian clock “regular” and on schedule.
For most, jumping ahead by 1 hour in the spring means losing an hour of sleep. This has been associated with an increased risk for stroke, cardiovascular events, motor vehicle collisions, crash fatalities, medical errors, hospitalization, psychiatric disorders and even suicide.
A large percentage of children, youth and adults across the country are chronically not getting enough sleep. When sleep is tenuous, resilience is reduced and other processes are more easily disrupted. Implications run the gamut from worse academic performance to increased physician burnout and catastrophic oil spills. Additionally, chronically curtailed sleep may increase likelihood of neurocognitive deficits, dementia, substance use and metabolic dysfunction.
In winter months, children and youth may be at school for hours before sunrise. Beyond decreased attentiveness, this means many school-age children wait for the school bus in darkness each morning; following nationwide extension of DST in the past, increased fatalities were observed. Additionally, youth driving to school drowsy may be at increased risk for collisions.
Cheng: Our bodies have a natural internal “clock,” known as the circadian rhythm, that regulates multiple biological systems. The strongest external cue for this rhythm is light, and when we are exposed to more light in the morning and less light in the evening, our circadian rhythm — and the body’s biological systems — are synchronized. Our natural body rhythm is aligned with standard time.
In contrast, changing clocks during DST throws off this balance and has many well-established harmful effects, including increased risk for motor vehicle fatalities, medical errors, cardiovascular events such as stroke and heart attacks, suicide and, for students, negative impacts on education. High school students lose sleep and have difficulty with attention after the change to DST.
Flynn-Evans: There are two main issues with this time change: First, we all lose an hour of sleep and, second, we have to shift our entire sleep schedule 1 hour earlier relative to standard time. Sleeping for an adequate duration of time — more than 7 hours — at a regular time at night is essential for optimal cognitive and physiological function. When the clocks change, that loss of an hour of sleep paired with waking up earlier leads to an increased risk of motor vehicle crashes, workplace accidents and medical events like heart attacks.
The season of DST means that we are exposed to light later in the day and more darkness in the morning. Our daily pattern of light exposure is what tells our circadian rhythm, or body clock, what time it is, which directly impacts when we feel sleepy and when we feel alert. The later light in the evening means that our bodies will prepare us for sleep later than during standard time. Because most people cannot sleep in to compensate for a later bedtime, this means that people obtain less sleep overall during DST.
It is harder to pin down these consequences, but we know that chronic sleep deprivation is associated with reduced cognitive and physiological well-being.
Mathew: Time change is more difficult for certain at-risk populations such as people with preexisting sleep difficulties, the elderly, shift workers and teenagers (who are sleep-deprived at baseline). Unless there is an intentional effort to adjust to the change, the time change in March results in loss of an hour of sleep, and the effects are felt over the next several days, affecting nighttime sleep and daytime functioning. This can affect what we do at school and in our workplaces.
In addition, there is evidence of an increase in motor vehicle accidents during the change to DST. There is also a higher risk of cardiovascular problems such as heart attacks, stroke, atrial fibrillation and mood disorders when we change from standard time to DST.
Spector: Changing to DST has negative repercussions on both physical and mental health. These range from an increased risk of heart attacks and strokes to more work-related accidents and car accidents. Mentally, following the time change, we see more medical errors and a higher risk for depression and suicide attempts.
Healio: Are there any benefits to daylight saving time?
Bhui: With increased evening light, there may be some decrease in crime and motor vehicle collisions, possibly because these tend to occur more commonly after dark. One of the original ideas behind DST was to save on energy costs. However, evidence to the contrary is mounting, and DST may even increase energy demand.
The main selling point of DST is the increase in evening sunlight. Youth and adults who go to school or work traditional hours may appreciate this because they have more “daytime” for afterschool or afterwork activities. However, evening light exposure delays melatonin release and can delay sleep onset, pushing back the sleep and wake times that feel natural. This presents an additional challenge for individuals who already struggle to wake up early in the morning to get to school or work on time.
Cheng: There are some reports that a subset of motor vehicle accidents occurs less often in the evening. However, the preponderance of evidence demonstrates the opposite effect: There are more motor vehicle accidents after changing to DST compared to standard time. In addition, safety of children would be jeopardized while waiting at the bus stop and walking to school during darker mornings after changing to DST.
Flynn-Evans: From a sleep perspective, there are no obvious measurable benefits to DST. At AASM, we endorse ending time changes in favor of permanent standard time because it better aligns with our bodies’ natural circadian rhythms.
Mathew: With DST, our internal sleep-wake rhythm is misaligned with the light-dark cycle, and this causes circadian disruption. The position of the AASM is that standard time aligns best with human circadian biology and provides distinct benefits for public health and safety, and it supports the elimination of DST.
Spector: Many benefits of DST have been reported over the years, such as lower crime rates and energy savings, but these do not hold up under closer scrutiny. If there is a benefit of DST, it is commercial. When daylight is shifted to later in the day, there might be more retail activity as people tend to shop more when it is light out.
Healio: Is it more difficult for individuals to “spring forward” or “fall back”?
Bhui: “Springing forward” causes jarring misalignment between our internal circadian time and wall clock time. It is widely accepted that delaying sleep is much easier than advancing it; consider how much more easily you can stay awake an extra hour or two beyond your usual bedtime to watch a movie, or finish your charting, than it is to fall asleep an hour or two earlier.
Additionally, while we can change the time on the clock, we cannot control the movement of the sun: Pushing the clock ahead by an hour simple means shifting 1 hour of sunlight from morning to evening. While “falling back” has been generally thought to be safer, there may also be an increase in traffic accidents around that time.
Cheng: Overall, it is more difficult to adjust to “springing forward.” It has been shown that biological markers of circadian rhythm take up to approximately 4 weeks to normalize after the change in DST compared with the change to standard time, or “falling back,” when values normalize more quickly.
This would especially apply to those who need more light in the morning to align their circadian rhythm, including adolescents, those in more western regions of the U.S. and, in general, in any modern society where there is a common overuse of social media in the evenings, which expose individuals to more light later in the day than is natural.
Flynn-Evans: About two-thirds of adults are “night owls,” which means they have a circadian period that is a little longer than 24 hours. This makes it easier to sleep later and harder to go to bed and get up earlier. This means that it is more difficult for most adults to “spring forward” because doing so requires everyone to shift their sleep an hour earlier relative to standard time.
Mathew: “Spring forward” is harder than “fall back” because we lose an hour of sleep with the time change in spring.
Spector: “Springing forward” is much more difficult than “falling back.” There is little risk associated with “falling back” because we all get an extra hour of sleep, and we are moving onto the time that more closely aligns with our body clocks. “Springing forward” is a problem because we are sleep deprived from getting an hour less sleep and wind up in a time zone that does not meet our body’s needs.
Healio: How do you recommend we adjust to the time change?
Bhui: While it may be difficult to completely avoid the harmful effects of jumping ahead, there are some strategies that can help. Before the switch, build up your sleep resilience by getting at least 7 to 8 hours of sleep each night and continue this afterward. In the days leading up to the time change, advance your daily schedule by 15 to 20 minutes. This helps reduce the impending “social jetlag,” or the discrepancy between your internal clock and the external clock.
Exercising, eating and a reduction in light exposure, including going to bed in a dark room, are additional cues for your internal clock, and outdoor bright light exposure early in the morning of the time change also can help sync clocks.
The evening before the time change, set your clocks 1 hour ahead and stick to your usual bedtime. Build and maintain healthy sleep habits, which include prioritizing regular bedtimes and wake times; getting at least 7 to 8 hours of sleep each night; keeping electronics and bright screens out of the bedroom; avoiding alcohol and caffeine beyond the beginning of the afternoon; making your sleep environment dark, quiet and cool; and resisting naps outside of your usual sleep period unless there are safety concerns.
Cheng: Aim to get at least 7 hours of sleep per night before and after the time change. Starting a few nights before the time change, gradually adjust bedtimes and rise times by shifting them 15 to 20 minutes earlier. Making earlier adjustments to daily routines, such as meals, can also cue your body in advance.
The night before DST, set clocks ahead 1 hour in the early evening, then go to bed at your normal bedtime. In the days following the time change, expose yourself to bright light — ideally sunlight — which will help your body realign to the time change.
Mathew: Our internal circadian rhythm works in sync with the outside light-dark cycle. Although it is only an hour, it is difficult for our internal circadian clock to make the change in one day. Our body likes routine and consistency, and abrupt change can be disruptive.
Going to bed earlier by about 15 minutes each day for 3 to 4 days prior to the time change can help with the transition. Children benefit from these strategies even more. Their meal and bedtimes should be moved up earlier, keeping in mind that children need more sleep than adults. Exposure to bright light in the morning helps with getting our circadian rhythm in sync with the light-dark cycle. Napping during the day may be tempting but should be avoided, as it makes the adjustment harder.
In addition, even after the time change, it is key to practice good sleep hygiene by keeping bedtime schedule consistent and aiming for adequate sleep duration — at least 7 to 8 hours a night for adults. Avoiding bright lights and screen time/devices close to bedtime and keeping the bedroom dark and cool facilitates sleep.
Spector: In advance of losing an hour of sleep this weekend, it is important to be well-rested so you can better absorb the shock to the system that comes from losing an hour and shifting time zones. People who have been getting good sleep before the time change will probably pull through more smoothly. I also recommend people minimize driving the day after the change when car accidents spike.
Reference:
- American Academy of Sleep Medicine continues to oppose permanent daylight saving time bill. https://aasm.org/aasm-opposes-permanent-daylight-saving-time-bill-sunshine-protection-act/. Posted March 2, 2023. Accessed March 10, 2023.
Editor’s note: This article was updated March 13, 2023, to add responses from Reeba Mathew, MD, FCCP.