Both the change of clocks to Daylight Saving Time (DST) and the continual observation of DST pose lethal threats to human health. Changing clocks causes acute harms that persist for several days or even several weeks.[Berk][Giuntella & Mazzonna][Roenneberg 2019–08][Smith] Continually observing DST causes chronic harms that last for months (in the case of seasonal observance) or years without end (in the case of year-round observance). We “never adjust”[Curtis][Holliday][Kalidindi][Kantermann][Livingston 2016][Watson] to DST — instead we sleep less long and less well than we need.
The abrupt move forward in springtime by one hour is well-known for its shock to body and mind — causing traffic deaths, workplace accidents, lost productivity, and hospitalizations. Incidence of stroke spikes by 9%[Watson] after changing clocks to DST in spring. Incidence of heart attack increases by a range of 24%[Brueck][Michigan][Sandhu] up to 50%[Peralta] the Monday after changing to DST, and this increase continues at a range of 5%[Livingston 2016] up to 15%[Livingston 2020][Reddy] in the week that follows. Even more notably, heart attack rates decrease by a range of 10%[Livingston] to 21%[Brueck][Michigan][Sandhu] after returning clocks to Standard Time in autumn.
Additionally, the observance itself of DST causes subtler but stronger harms. Healthful sleep is necessary for prosperity and longevity, and it’s biologically regulated by melatonin and cortisol. The body’s natural release of these sleeping and waking hormones is tuned to the setting and rising of the sun. DST postpones both sunset and sunrise on our social clock, which disrupts the body’s hormone balance, and leads people both to stay awake late and to feel a need to sleep late.[CBC][Crick][Cytowic][Giuntella & Mazzonna][Gu][Ingraham][Lindsay 2019–12–05][Livingston 2020][O’Callaghan][Reddy] However, social schedules demand we wake on time regardless of how we feel, and permanent DST would demand most citizens to start school or work before sunrise for a third of the year (whereas most do not now).[Block & Meijer][CBC][Herf & Longcore][Juda][Labbe][Lindsay 2019–12–05][Meijer & Foster]
DST’s combination of late daylight and pre-sunrise waking robs us of 19 minutes of sleep every night on average.[Cermakian][Curtis][Giuntella & Mazzonna][Roenneberg 2019–08] Cortisol rhythms advance only two minutes despite clocks being advanced 60 minutes under DST.[Roenneberg 2019–08] This creates a “social jet lag”, which is far worse for health than ordinary jet lag, and which never is relieved under permanent DST.[Borisenkov][Clay][EBRS][Fletcher][Giuntella & Mazzonna][Gu][Herf][Juda][McMillan][Roenneberg 2019–08][SRBR] The body attempts to compensate by sleeping late on non–work days, but the benefits of sleep can’t be stored.[Borisenkov][Gu][Roenneberg 2019–08]
Researchers warn DST’s chronic lack of sleep “significantly”[Cermakian][Curtis][Giuntella & Mazzonna][Gu][Lewy][Roenneberg 2019–08][VoPham] increases risks of heart disease, stroke, diabetes, cancer, high blood pressure, obesity, metabolic disorders, personality disorders, unintentional midday sleep, caffeine abuse, alcohol abuse, depression, and suicidality. It harms cognition, productivity, reaction time, stress management, immunity, and life expectancy, in both children and adults.[BBC][Block & Meijer][Borisenkov][CBC][Cermakian][Clay][COFCO][Crawford & Boynton][Crick][Curtis][Daily Hive][EBRS][Gibson & Schrader][Giuntella & Mazzonna][Gu][Herf][Herf & Longcore][Herring][Ingraham][Jin & Ziebarth][Kalidindi][Karamali][Lindsay 2019–12–05][McCoy][Meijer & Foster][Merline][O’Callaghan][Ogliore][RIVM][Roenneberg 2019–08][SRBR][Watson][White][Zantinge] Delaying sunset and sunrise by one hour increases rates of breast cancer by 5%[Ingraham] to 12%,[Herf & Longcore] heart disease by 11%,[Crick] prostate cancer by 12%,[Herf][Herf & Longcore] colorectal cancer by 13.5%,[Herf] lung cancer by 13.8%,[Herf] heart attack by 19%,[Ingraham] liver cancer by 21%[Herf & Longcore] to 33%,[Herf] stomach cancer by 27%,[Herf] uterine cancer by 30%,[Herf][Herf & Longcore] leukemia by 36%[Herf & Longcore] to 39%,[Herf] and esophageal cancer by 48%.[Herf] Seasonal depression is more prevalent at northerly latitudes (10% of Seattle, 25% of Alaska[Herf]), where winter days are unavoidably shorter. This suffering is most effectively relieved by adding light to mornings — not evenings.[Gillmore][McCoy][Roenneberg 2019–08] Desire for DST’s artificially brighter evenings has been compared by scientists to desire for the pleasure of smoking, in that it ignores the overwhelming volume of data that proves the harm each practice inflicts on individuals and society.[Junge & Cunnington]
Proponents of DST claim the practice increases exercise. Circadian scientists consider this claim “debunked”.[Watson] Increases in physical activity are better attributed to the natural change of season, not the artificial change of clocks.[SRBR] The study to back DST’s exercise claim only considered regions that observe summer DST (ignoring those on permanent Standard Time), its gains averaged just two minutes per day (not the full hour the clock gets advanced), and these small gains were seen only in Europe and Australia (with no gains in America).[Livingston 2016] Another study that did compare close regions with different time observations found no increase or decrease in exercise.[Kalidindi][Zick] Furthermore, evening exercise can disrupt sleep, and lack of sleep can increase sports injuries by 70%.[Herf]
Circadian-health experts around the world “unanimously”[Juda][Fletcher][Lindsay 2019–12–05] endorse permanent Standard Time for health, safety, and prosperity as scientific “consensus”.[Bui][Ogliore] Noteworthy organizations include the Society for Research on Biological Rhythms (representing over 700 researchers from over 40 countries),[Roenneberg 2019–06] the Center for Circadian Biology,[Ackerman] the Canadian Society for Chronobiology,[Cermakian] the European Biological Rhythms Society,[EBRS] and the European Sleep Research Society.[ESRS] See Save Standard Time’s list of policy endorsements for additional organizations and individuals of note who reject permanent DST and support permanent Standard Time.