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The U.S. Senate quietly and unexpectedly passed the Sunshine Protection Act in a unanimous vote, bringing Americans one step closer to permanent Daylight Savings Time (DST) for the entire year. The ritual of switching between DST and standard time has been ongoing in the U.S. for over a century, with debates recently intensifying as to whether the ritual is necessary, tedious, or even deadly.
Several recent epidemiological and clinical studies point to evidence of increased mortality and medical risks in the week of the shift to DST, and sometimes also in the week shifting back to standard time. These studies include:
- A 2020 Current Biology study noted increases in fatal traffic accidents by 5 percent during the DST spring shift, especially on West Coast mornings (theorized due to less alertness without AM light).
- A 2015 Sleep Medicine study in Finland noted an increase in the rates of strokes during the DST shift week—as much as 8 percent higher from 2004 to 2013, especially in people with cancer or over age 65.
- A 2019 Journal of Clinical Medicine metaanalysis of 7 studies noted a higher risk of MI in the weeks following both transitions.
- Some studies note a possible increase in cancer rates on the West Coast after DST kicks in, and also an increase in the western edges of time zones. (There are hypotheses that decreased melatonin signaling or shifting caused by daylight shifts may increase the risk of cancer.)
- A 2017 Denmark study showed an 11 percent increase in depressive episodes after the winter shift back to standard time. (In general, lack of winter daylight is a risk factor for winter seasonal affective disorder.)
Other consequences include missed medical appointments and increased complaints of cognitive issues and fatigue during both shift weeks, although the DST shift is arguably more difficult due to a potential loss of one hour of sleep.
In particular, there are concerns that children, especially adolescents, are less functional due to chronic sleep deficiency caused by early morning public school schedules, which are even more exacerbated by DST. Some evidence indicates that most teens have a delayed sleep phase at baseline and need to sleep in more to aid their spurt in growth and development and cognitive status. A study in the Journal of Neuroscience, Psychology, and Economics examining standardized testing scores in Indiana between 1997 and 2006 noted that SAT scores decreased by 16 points in schools that follow DST.
Aside from the risks of the time shifting back and forth, there are concerns about permanently keeping DST vs. standard time. Sleep experts seem to prefer permanent standard time instead. While most people enjoy the longer PM daylight hours from DST, the tradeoff of permanent DST would be increased morning darkness in the winter.
Dr. Charles Czeisler, a sleep specialist at Harvard, noted that in winter, a one hour earlier shift with dark mornings may have adverse effects due to our internal natural circadian rhythms; we need the sun to wake us up. On the shortest winter day, the sun wouldn't rise until 8 or 9 AM instead of 7 or 8 AM across most of the country. Longer daylight hours in the winter also may cause increased disrupted night sleep and decreased melatonin signaling. There may also be increased energy usage on dark cold mornings (although these energy shifts can also rise in the summer evenings due to DST).
It seems either shift may have pros and cons, and either shift has data that shows increased rates of pedestrian accidents due to darkness caused by either end of the day changing. Also, in turn, a permanent shift one way or another has its pros and cons as well.
In the end, most of us may just have to settle for whatever choice the experts and government decide to use and make our individual adjustments accordingly. We can prepare in advance with attention to shifting our sleep schedules or lighting arrangements during the shift weeks, and if the shift itself disappears—we will need to pay attention to how to best adjust to the new normal.
