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Daylight Saving Time

January 26, 2022
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WRITTEN BY Dr. Alan Moss and Dr. Joshua Mueller

Executive Summary 

Daylight Saving Time (DST), which is the practice of adjusting clock times forwards or back at certain points in the year to change clock time alignment with sunrise and sunset, is observed in approximately 70 countries, including the U.S. DST was first established in the U.S. in 1918 by the Standard Time Act, and has been modified several times since then, most recently in 2005 by the Energy Policy Act. While federal statute establishes nationwide DST observance, states may take legislative or executive action to opt out. Several studies find various effects of shifting clocks ahead on health, energy use, and commerce, but there is less evidence for significant effects due to shifting back to standard time, or having differential light levels between DST and standard time. House Bills 1735, 1761, filed during the 2022 regular legislative session, would make DST permanent in Missouri pending similar action by bordering states. Conversely, HB 1889 would make Standard Time permanent (i.e., eliminate MO’s adherence to DST).

Highlights 

  • As of 2021, 19 states have taken action to make DST permanent (subject to federal statutory changes). Arizona and Hawaii and several U.S. territories have opted out of DST observance, and adhere to standard time year-round.
  • Studies find that the risk of heart attack is approximately 5% higher in the first week after entering DST, and that the risk of ischemic stroke has also been found to be elevated by about 8% for the first two days after entering DST.
  • Keeping DST in place year-round has been estimated to reduce pedestrian fatalities by about 170/year and motor vehicle fatalities by 195/year.
  • Studies have found that DST switches are typically associated with decreases in stock market  returns and worker productivity immediately after switches. 

Limitations 

  • Individuals with circadian rhythm disorders, neurological disorders, or children/adolescents whose brains are still developing may be more susceptible to the negative health effects related to the DST transition, but more evidence is needed.
  • Overall, there is little evidence as to whether DST decreases or increases energy use, and no evidence that DST poses increased safety risks to school-aged children or decreases their academic performance.
  • Research on the broad economic effects of DST is not conclusive.
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