The Dark Side of Daylight Savings
Daylight Savings Time (DST) is a century-old practice that aims to conserve energy by making better use of daylight during the spring and summer months when the days are longer. However, recent research actually suggests that there are little to no effect on energy cost savings.1 Lately, it has become a controversial topic with many regions of the world proposing to end this custom, which is practiced by about 2 billion people in the world, mainly in North America and Europe. In the United States, it is actually estimated that DST costs the economy over $400 million a year in losses due to injuries, productivity loss and health effects.2 Our biological clocks are just not flexible enough to this twice-yearly change that disrupts our circadian rhythms. This change is akin to the symptoms we experience with jetlag, albeit a bit more subtle, as our bodies adjust to the new time.
There is a large body of research supporting the harmful effects of DST. A meta-analysis review of seven studies, consisting of over 115,000 participants in total, looked at the risk of heart attack following DST transitions and found that the two weeks following spring, but not the autumn DST transitions were associated with a statistically significant, but modest, increase in the risk of heart attacks.3 Similarly, the risk of stroke-related hospitalizations was increased within the first two days after either DST switch in a nationwide study in Finland that spanned almost 10 years.4 In this study, a higher risk was observed in women than men, and in those older than 65 or with comorbidities. Another recent study in 2020, analyzing U.S. and Swedish population data found a greater risk of a whole spectrum of diseases, including immune-related and digestive system disorders, infections and injuries associated with the spring shift specifically.5 Many of the diseases were associated with a roughly 10% relative risk increase within the first week following the spring DST shift, leading the authors to estimate that DST is associated with ~150,000 incidence of negative health effects in the United States, and over 880,000 cases globally.
Interestingly, it seems that the spring time shift has a more substantial effect on our health than the change that occurs in the fall. One possible explanation is that the spring shift is usually associated with one hour less of sleep than a normal night and this transient, mild stressor could exacerbate or trigger an adverse health condition. Although the spring change can be more difficult, the fall time change shortens our daylight hours after work – leading to less activity in the evenings and seasonal affective disorder in many people. Studies have observed a short-term increase in depression episodes and male suicide rates following DST.6 It is also important to look at this data and realize that DST may not be the causative agent because correlation is not causation and there are many caveats to each of these observational studies. One thing to consider is that likely these diseases were developing in individuals long before the actual diagnosis was made, and the mild stressor of DST probably acted to trigger or worsen their pre-existing condition.
Studies have also shown that more car accidents occur on the first workday after DST.7,8 One of these studies showed that eliminating DST would prevent approximately 28 fatal car accidents a year in the United States.8 There’s even some evidence that judges even give out harsher sentences (5% longer in duration) on the Monday following DST, likely due to the short-term effects that loss of sleep or fatigue have on one’s mood.9 DST even has been associated with lower student SAT scores10 and poor stock market returns11.
Although the short-term acute effects of DST are well-documented, the long-term implications on our health and wellbeing are less understood. All of this data begs the question, do we really need to continue with this practice? Many parts of the world do not practice DST and legislative efforts to end this practice are increasing. Unfortunately, neighboring states or countries with different practices can complicate this process and is one of the key reasons for the reluctance to change.
In the meantime, those of us who must suffer through DST twice a year can make some minor lifestyle changes to lessen the impact of each time shift. The easiest approach is to adjust your alarm by 10-15 minutes per day over the four to five days before the switch is to take place. This means going to bed a bit later and sleeping in a little bit longer in the morning in the fall, or going to sleep earlier and waking up earlier in the spring prior to the changes occur. Practicing other healthy habits, like regular exercise, staying hydrated and not over-caffeinating can also ease the inevitable transition. Having these tools and being mindful of the increased fatigue can help protect and lessen the impact of DST.
- Aries MBC, Newsham GR. Effect of daylight saving time on lighting energy use: A literature review. Energy Policy. 2008;36(6):1858–1866.
- Chmura Economics and Analytics. The Lost Hour Economic Index: Estimating the Economic Loss of Daylight Saving Time for U.S. Metropolitan Statistical Areas. 2013. Available at: https://sleepbetter.org/lost-hour-release/ (Accessed March 4, 2022).
- Manfredini R, Fabbian F, Cappadona R, et al. Daylight Saving Time and Acute Myocardial Infarction: A Meta-Analysis. JCM. 2019;8(3):404.
- Sipilä JOT, Ruuskanen JO, Rautava P, Kytö V. Changes in ischemic stroke occurrence following daylight saving time transitions. Sleep Medicine. 2016;27–28:20–24.
- 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.
- 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.
- Coren S. Daylight Savings Time and Traffic Accidents. N Engl J Med. 1996;334(14):924–925.
- Fritz J, VoPham T, Wright KP, Vetter C. A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk. Current Biology. 2020;30(4):729-735.e2.
- Cho K, Barnes CM, Guanara CL. Sleepy Punishers Are Harsh Punishers: Daylight Saving Time and Legal Sentences. Psychol Sci. 2017;28(2):242–247.
- Gaski JF, Sagarin J. Detrimental effects of daylight-saving time on SAT scores. Journal of Neuroscience, Psychology, and Economics. 2011;4(1):44–53.
- Kamstra MJ, Kramer LA, Levi MD. Losing Sleep at the Market: The Daylight Saving Anomaly. American Economic Review. 2000;90(4):1005–1011.