Although the United States has observed daylight saving time (DST) continuously, in some form, for the last 5 decades (Table), the twice a year switches have never been less popular. In 2019, an American Academy of Sleep Medicine (AASM) survey of more than 2,000 US adults found that 63% support the elimination of seasonal time changes in favor of a national, fixed, year-round time, and only 11% oppose it. Indeed, multiple states have pending legislations to adopt year-round daylight saving time or year-round standard time (Updated September 30, 2020, Congressional Research Service. https://crsreports.congress.gov. R45208 Daylight Saving Time. Accessed Dec 14, 2020). Adjacent states, to limit confusion to interstate travel and commerce, tend to lobby for similar changes together. Most importantly, because of the scientific evidence of detrimental health effects to the public and safety concerns, the American Academy of Sleep Medicine has issued a position statement for year-round standard time (Rishi MA, et al. Daylight saving time: an American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2020;16(10):1781).
Dr. Kin M. Yuen
Railroad industry successfully lobbied the US government for consistent time in the United States to keep transportation schedules uniform in 1883; standard time was implemented. When war efforts were over, DST was dropped. Some regions, such as New York and Chicago, maintained DST, but no national standard was applied. Retailers and the recreational activity industry advocated for DST to increase business after work in the afternoon and evenings. In 1966, Congress passed the Uniform Time Act of 1966 to implement 6 months of DST and 6 months of standard time (Waxman OB. The real reason why daylight saving time is a thing. https://time.com/4549397/daylight-saving-time-history-politics/; November 1, 2017. Accessed Dec 14, 2020). Local jurisdictions can opt out of DST, but it requires an act of congress to enforce perennial DST.
When the OPEC embargo occurred, the Emergency Daylight Saving Time Energy Conservation Act was enacted in 1973, but it was quickly ended in October 1974 due to its unpopularity. The dairy industry was opposed to earlier rise time that disrupted the animals’ feeding schedules and their farm operations (Feldman R. Five myths about daylight saving time. https://www.washingtonpost.com/opinions/five-myths-about-daylight-saving-time/2015/03/06/970092d4-c2c1-11e4-9271-610273846239_story.html. Accessed Dec 14, 2020.). Public safety was raised as a concern as early as 1975. The Department of Transportation found increased fatalities of school-aged children in the mornings from January to April of 1974 as compared with 1973. However, the National Bureau of Standards, that performed a review subsequently, stated that other factors might also be at play. Further extension of DST from 6 months of the year to the subsequent 7, and then 8 months per year were enacted in 1986 and 2005, respectively (The reasoning behind changing daylight saving. https://www.npr.org/templates/story/story.php?storyId=7779869. NPR. Accessed Nov 1, 2020.)
An exemption of a state from DST is allowable under existing law, but to establish permanent DST will require an act of Congress. Since then, Arizona and Hawaii, as well as US territories, such as Puerto Rico, Guam, American Samoa and Northern Mariana Islands, and US Virgin Islands, have all opted out of DST by state exemption. Because of Hawaii’s proximity to the equator, the timing of sunrise and sunset were fairly constant throughout the year that made DST unnecessary. The Navajo Nation in Arizona, because of its extension into adjacent New Mexico and Utah, participates in DST. Most of the countries along the tropics, parts of Australia, China, Japan, South Korea, India, and majority of African countries do not observe DST. The European Union has voted to abolish twice yearly change in time in 2021; and individual member states will be able to decide whether they wish to remain on permanent standard time or DST. Since 2015, more than 45 states have proposed legislation to change their observance of DST.
The human biological rhythm is most consistent with standard time (Antle M. Circadian rhythm expert argues against permanent daylight saving time. https://www.ucalgary.ca/news/circadian-rhythm-expert-argues-against-permanent-daylight-saving-time. Accessed Dec 14, 2020.). Since the biological clock for most individuals is not exactly 24 hours long, zeitgebers such as sunlight, exercise, and feeding behaviors are important time cues to foster a regular rhythm. Acutely, the adjustment to 1 hour’s sleep loss at the spring switch from standard time to DST generally requires several days to adapt (Kalidindi A. Daylight saving time is bad for your health. https://massivesci.com/articles/daylight-saving-savings-time-dst-november-standard-time. Accessed Dec 14, 2020.). During this adjustment period, the internal bodily functions are disrupted. The sense of sleepiness and fatigue are increased with earlier morning awakenings, and the inability to fall asleep earlier leads to symptoms of insomnia and poor sleep quality.
The health and economic costs due to accidents, injuries, and medical errors are now well known. Individual biological rhythm disruptions at the spring switch from standard time to DST with the loss of sleep likely contributes to higher risks of myocardial infarctions (Janszky I, et al. Shifts to and from daylight saving time and incidence of myocardial infarction. N Engl J Med. 2008; 359(18):1966) that are not mostly seen during the fall switch from DST to standard time. An estimated 40 minutes of sleep loss occurs within the Sunday to Monday transition of DST in the spring. Medical errors, car crashes, suicide risks, and fatigue are all reportedly higher on the Monday after the spring switch. Some of these effects have been cited as remaining elevated through the first week and possibly chronically during the entire duration of DST. Some people have difficulty adapting to sleep loss from DST, creating social jetlag, and complaints of fatigue and increased prevalence of metabolic syndromes are more common in this population (Koopman ADM, et al. The association between social jetlag, the metabolic syndrome, and type 2 diabetes mellitus in the general population: The New Hoorn study. J Biol Rhythms. 2017 Aug:32(4):359; Roenneberg T, et al. Social jetlag and obesity. Curr Biol. 2012 May 22; 22(10):939). “Cyber-loafing,” describing those at work but who chose to peruse entertaining websites, reportedly occurred more during DST compared with the fall.
Delaying school start time has been associated with improved school attendance and performance. The American Academy of Pediatrics and AASM support delaying school start time; this measure has been adopted by California, and legislation is pending in other states (https://www.startschoollater.net/legislation.html). In spring, the loss of 1 hour’s sleep would negate any benefit of beginning the school day later. Students would suffer inattention, decrease ability to focus, and be less effective learners. Obesity and metabolic syndromes that have been found in adults, are also observed in children whose biological rhythms are delayed compared with their peers who have morning lark tendencies. Risks of mood disorder may be elevated at onset of DST due to earlier arise time or standard time when less sunlight is available in the evenings.
During the current pandemic with SARS-CoV-2, there are new reports of teens and college students able to obtain more sleep because of online education (How children’s sleep habits have changed in the pandemic. https://www.nytimes.com/2020/08/17/well/family/children-sleep-pandemic.html. Accessed Dec 14, 2020.) and they had more restful sleep and improved mood. This positive trend will be monitored closely with some schools returning to in-person instruction.
Societal costs of decreased productivity, on the job accidents and injuries, and increased risk of motor vehicle crashes (Robb D, et al. Accident rates and the impact of daylight saving transitions. Accid Anal Prev. 2018 Feb; 111:193), in addition to individual well-being, have also been reported. Energy savings that propelled arguments for DST did not translate into significant savings after all. Although less electricity was used with more abundance of sunlight in the afternoon, people drove more and used more gasoline to attend their after work activities.
Adaptation of a year-round time schedule will need to balance the impact and disruption to the health and well-being of its citizens, as well as the interests of its commercial sector. The argument for maintaining year-round standard time states that to prevent the loss of the 1 hour’s sleep that DST creates in the spring. Therefore, it preserves a more aligned biological rhythm, lowers the risks of preventable myocardial infarction, improves attention and focus, lessens daytime fatigue, and improves sense of well-being year round. Certainly, it will ensure that the teens who are likely to have later sleep schedules, will not lose more sleep and negate the benefit of starting school later.
Timeline for DST
1784 Benjamin Franklin advocated to rise earlier so as to burn fewer candles in the evenings.
1883 Railroads need standard time for operations.
1890 Merchants and retailers (clothing, cigars) advocated for longer shopping hours.
1916 Germany conserves energy.
1918 DST: fuel conservation during World War I.
1942 DST during World War II.
1963 “Chaos of clocks” needs uniform time for commerce.
1966 Uniform Time Act: DST 6 months per year.
1973 Emergency DST Energy Conservation Act: Arab oil embargo to extend DST to 8 months; ended prematurely in October 1974.
1986 Extended start date from last Sunday of April to first Sunday of November.
2005 Energy Act of 2005: 2nd week of March.
Dr. Yuen is Assistant Professor, UCSF Department of Internal Medicine-Pulmonary Department, and Adjunct Clinical Assistant Professor at Department of Psychiatry & Behavioral Sciences at Stanford (Calif.) University. Dr. Rishi is Consultant – Pulmonary, Critical Care and Sleep Medicine, Mayo Clinic Health System, Eau Claire, WI; and Assistant Professor of Medicine, Alix School of Medicine, Mayo Clinic, Rochester, MN.
Correction 3/16/21: A photo caption in an earlier version of this article misstated Dr. Kin Yuen's name.