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Is Daylight Savings Time Toxic to Our Physical, Emotional, and Mental Health?
Every year we adjust our clocks twice to get more daylight after working hours: once in the spring (“spring forward”) and once in the fall (“fall back”). While these shifts may have been suggested as a good idea in the early days of farming and waking up early to get more done, in addition to energy conservation, we now know that altering natural rhythms can be unhealthy, if not toxic to our physical health and even social behaviors (1). Furthermore, it creates upset in global communication considering that not all countries adhere to this forward motion of the clock at the same time, if at all. In 2020, the American Academy of Sleep Medicine came out with a published position statement advocating the abolishment of daylight savings time (DST) due to its effects on health (2).
Our circadian rhythms are not set by the social clock, but by the natural light-dark cycle. Research on DST has shown that making this change every year could result in significant negative impacts on our health and well-being (3).
For this discussion, it’s helpful to make a few distinctions:
Social clock: time on the clock that we can define and manipulate as we wish
Solar clock: time determined as the sun rises and sets, with noon being the midpoint
Body clock: inherent wake and sleep times set by our circadian rhythm
In the northern hemisphere, each spring, we move the clocks forward to enjoy more light in the evening. This is the part of the year we are in DST. Even though it is only one hour, it is disruptive to our physical, emotional, social, and mental health (1). When we make this shift, our body clock is no longer synchronized with the clock time because the light in the evening makes it harder to fall asleep and shifts our body clock later. Compounding this disruption to our natural circadian rhythm we now also wake earlier, in darkness, making it harder to wake up and further throwing off our ability to fall asleep at night.
There is compelling research to suggest that following one’s circadian rhythm is crucial to overall health.
With DST starting in March and going until early November, our body clock is out of sync with its natural rhythm as our days are dictated by our daylight savings social clock. Then in the fall, we move the clocks back to Standard Time, aligning with the solar day and getting more light in the morning and darkness at night. These four months a year are the only time when the solar clock, social clock, and our body clock are aligned. The chronic effects of switching to DST can last for months, as people’s inherent body clocks do not align with the clock time when it is disconnected from the environmental light-dark cycle (4). Chronic misalignment is associated with decreased life expectancy, mental health challenges, and decreased cognitive performance (4-6).
Therefore, most of the year (for eight months), we are out of alignment with the natural rhythm.
Physical health impacts of DST
The most obvious impact on health and well-being is sleep. In spring, people lose one hour of sleep due to the circadian rhythm challenges from the abrupt change (7). Throwing off circadian rhythm means changing our eating, physical activities, and overall behavior, which can then lead, over time, to more chronic issues such as increased risks for cerebrovascular (1) and cardiovascular events (8), immune-related diseases (9), and even changes in physical performance (10)and workplace injuries (11).
The acute effects of switching to DST include increased cardiovascular events such as heart attacks, which have been documented to increase by 4-29% (8). Autopsy data collected before and after the spring change to DST show an increase in deaths during the week immediately following the change. Specifically, there is a significant increase in non-natural deaths, including traffic collisions and suicide, and in natural deaths, such as cardiac insufficiency and heart attacks.
However, no increase in autopsies is seen in the fall when people gain an extra hour of rest and have the chance to align their body clock with the solar day (12). Another study concluded that just a “one-hour change of the clock may impact population health significantly” after finding an increase in injuries, complications due to pregnancy and childbirth, noninfective enteritis and colitis, and circulatory diseases (1).
Emotional-mental health impacts of DST
One of the biggest impacts of DST are felt through emotional-mental health. It is well known from sleep research published by Matthew Walker, PhD, and others, that sleep deprivation can impair mood, alertness, and alter how we perceive emotional states (1,13,14). For example, one study found that there could be associations between depressive episodes and the transition into DST (15). Just one hour of sleep loss through the transition to DST has been found to translate to changes in the brain registered through fMRI (a way to scan the brain’s activity) that results in less activity in the social cognitive areas of the brain (16). These physiological changes have been shown in real-world settings to change people’s interactions to make them less prone to helping each other and even less charitable giving (16).
Has DST been repealed?
In 1974, the clocks stayed on DST over the winter. However, this change was repealed after one year due to the difficulty of children and workers traveling to school or work in the morning darkness (17). In March 2022, the U.S. Senate passed the Sunshine Protection Act, which would put the U.S. permanently on DST, starting in November 2023. The bill has yet to pass the U.S. House of Representatives, so it is unclear whether this change will be implemented (18). The American Academy of Sleep Medicine (the leading sleep and circadian expert group in the U.S.) suggests that seasonal time changes be abolished entirely (7). However, contrary to changes proposed by the Sunshine Protection Act, they strongly support permanent Standard Time, which is more closely aligned with our circadian biology (7). Standard Time strives to align with the solar clock, in which noon is when the sun is at its’ highest. Therefore, during Standard Time, we get equal hours of light before and after noon. Most important for human health, the environmental day and our circadian clock align on Standard Time, allowing for both good quality and sufficient sleep. Until two hundred years ago, with the invention of electric light, we organized ourselves around the solar clock for most of human history.
Tips for Easing into DST
Even though we are still subject to DST, there are smart strategies to help adjust to it each spring. Here are some tips to make the transition easier for overall health:
Go to bed 15 minutes earlier for the three days beforehand. This subtle change allows you to shift your sleep schedule gradually.
Continue to get bright light for 30 minutes soon after waking each morning.
You can also take a low dose of phytomelatonin 0.3 mg at bedtime to help you sleep or 6 hours before bedtime to shift your body clock earlier for five to seven days before DST takes effect.
Written by Catherine Darley, ND
Reviewed by Deanna Minich, PhD
March 7, 2023
1. Zhang H, Dahlén T, Khan A, Edgren G, Rzhetsky A. Measurable health effects associated with the daylight saving time shift. PLoS Comput Biol. 2020;16(6):e1007927. doi:10.1371/journal.pcbi.1007927
2. Osborne‐Christenson EJ. Saving light, losing lives: How daylight saving time impacts deaths from suicide and substance abuse. Health Econ. 2022;31(S2):40-68. doi:10.1002/hec.4581
3. Roenneberg T, Wirz-Justice A, Skene DJ, et al. Why Should We Abolish Daylight Saving Time? J Biol Rhythms. 2019;34(3):227-230. doi:10.1177/0748730419854197
4. Borisenkov MF. Latitude of residence and position in time zone are predictors of cancer incidence, cancer mortality, and life expectancy at birth. Chronobiol Int. 2011;28(2):155-162. doi:10.3109/07420528.2010.541312
5. Foster RG, Peirson SN, Wulff K, Winnebeck E, Vetter C, Roenneberg T. Sleep and circadian rhythm disruption in social jetlag and mental illness. Prog Mol Biol Transl Sci. 2013;119:325-346. doi:10.1016/B978-0-12-396971-2.00011-7
6. Díaz-Morales JF, Escribano C. Social jetlag, academic achievement and cognitive performance: Understanding gender/sex differences. Chronobiol Int. 2015;32(6):822-831. doi:10.3109/07420528.2015.1041599
7. Rishi MA, Ahmed O, Barrantes Perez JH, et al. Daylight saving time: an American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2020;16(10):1781-1784. doi:10.5664/jcsm.8780
8. Manfredini R, Fabbian F, De Giorgi A, et al. Daylight saving time and myocardial infarction: should we be worried? A review of the evidence. Eur Rev Med Pharmacol Sci. 2018;22(3):750-755. doi:10.26355/eurrev_201802_14306
9. Mo Z, Scheben A, Steinberg J, Siepel A, Martienssen R. Circadian immunity, sunrise time and the seasonality of respiratory infections. medRxiv. Published online March 31, 2021. doi:10.1101/2021.03.29.21254556
10. O’Connor PJ, Kancheva M. Marathon run performance on daylight savings time transition days: results from a natural experiment. Chronobiol Int. 2022;39(1):151-157. doi:10.1080/07420528.2021.1974471
11. Barnes CM, Wagner DT. Changing to daylight saving time cuts into sleep and increases workplace injuries. Journal of Applied Psychology. 2009;94(5):1305-1317. doi:10.1037/a0015320
12. Lindenberger LM, Ackermann H, Parzeller M. The controversial debate about daylight saving time (DST)—results of a retrospective forensic autopsy study in Frankfurt/Main (Germany) over 10 years (2006–2015). Int J Legal Med. 2019;133(4):1259-1265. doi:10.1007/s00414-018-1960-z
13. Ben Simon E, Vallat R, Barnes CM, Walker MP. Sleep Loss and the Socio-Emotional Brain. Trends Cogn Sci. 2020;24(6):435-450. doi:10.1016/j.tics.2020.02.003
14. van der Helm E, Gujar N, Walker MP. Sleep Deprivation Impairs the Accurate Recognition of Human Emotions. Sleep. 2010;33(3):335-342. doi:10.1093/sleep/33.3.335
15. Hansen BT, Sønderskov KM, Hageman I, Dinesen PT, Østergaard SD. Daylight Savings Time Transitions and the Incidence Rate of Unipolar Depressive Episodes. Epidemiology. 2017;28(3):346-353. doi:10.1097/EDE.0000000000000580
16. Ben Simon E, Vallat R, Rossi A, Walker MP. Sleep loss leads to the withdrawal of human helping across individuals, groups, and large-scale societies. PLoS Biol. 2022;20(8):e3001733. doi:10.1371/journal.pbio.3001733
17. Beaujon A. The US Tried Permanent Daylight Saving Time in the ‘70s. People Hated It. . Washingtonion. https://www.washingtonian.com/2022/03/15/the-us-tried-permanent-daylight-saving-time-in-the-70s-people-hated-it/. Published March 15, 2022. Accessed July 2, 2023.
18. GovTrack.us. Sunshine Protection Act of 2021. H.R. 69 – 117th Congress: ; 2023. Accessed July 2, 2023. https://www.govtrack.us/congress/bills/117/hr69