Like clockwork, another round of Daylight Savings Time (DST) is upon us, and with it comes another debate over whether we should be “springing forward” and “falling back” in the first place.
A bipartisan group of 12 Senators is trying to end clock-switching in the United States with a bill called the ‘Sunshine Protection Act,’ which would make Daylight Savings Time permanent. They argue the switch will keep afternoons brighter for longer, resulting in a number of social and economic benefits.
However, several members of the House of Representatives disagree. They contend that while the Senate’s instincts are correct to revisit the need for clock-switching, the scientific evidence shows that Permanent Standard Time (PST) would be the better option for public health.
The true effects of daylight saving are not well researched, because it’s not possible to conduct a randomized control experiment on the issue, and observational studies have significant limits. Since there are so many possible confounding variables, the findings from observational studies often contradict each other, and are prone to misjudging causation. The field also appears to be lacking strong systematic reviews to determine the quality of existing research.
Below are some common claims in the debate over clock-switching, and the science being used to inform those claims.
Better sleep, improved health
While there is a wide consensus that sleep deprivation and circadian misalignment cause health and safety risks, many sleep scientists believe the effects of DST are still poorly understood.
Supporters of making Daylight Savings Time permanent argue it will result in better sleep, more exercise, and reduced risk of seasonal depression, heart problems, and stroke. But a closer look at the evidence reveals a more nuanced story.
While several of the studies examine the health effects of clock-switching in the days and weeks following the change (many of which undermine the claims that DST has positive health effects), there is limited research surrounding the long-term effects of living in DST versus PST.
A 2019 study in the Journal of Health Economics found that an extra hour of evening light led to 19 fewer minutes of sleep, on average. Since sleep deprivation has been shown to cause several health and safety problems, this could support the case for Permanent Standard Time, however, there is no study that can definitively confirm PST is the healthier ongoing lifestyle choice.
The American Academy of Sleep Medicine published a position statement in the Journal of Clinical Sleep Medicine that calls for an end to Daylight Savings Time in favor of Permanent Standard Time. It concludes:
“Existing data support the elimination of seasonal time changes in favor of a fixed, year-round time. DST can cause misalignment between the biological clock and environmental clock, resulting in significant health and public safety-related consequences, especially in the days immediately following the annual change to DST. A change to permanent standard time is best aligned with human circadian biology and has the potential to produce beneficial effects for public health and safety.”
This position is aligned with the European Sleep Research Society, European Biological Rhythms Society, and Society for Research on Biological Rhythms.
The Society for Research on Biological Rhythms (SBRR) also sponsored an expert review that compared large populations living in DST or Standard Time, and living on western or eastern edges of time zones. It concluded that it’s better to live in Permanent Standard Time than DST or switching back and forth.
The SBRR report stated that although the chronic effects of DST have not been studied directly, DST increases the time difference between the social clock and the body clock. Studies show these time differences can impact life expectancy, sleep, and mental and cognitive issues.
In any case, the clock-switching itself takes a damaging toll on our minds and bodies. According to the American Academy of Sleep Medicine, there is growing evidence that indicates changing time, especially from standard time to DST and back, increases the risk of cardiovascular events, metabolic disease, mood disorders, and other bad health outcomes.
Reduced energy costs
Supporters of making Daylight Savings Time permanent argue that more sunlight will reduce the demand for energy, such as electricity and gas. One study, which used a “natural experiment” in Indiana, found that DST actually increased residential electricity demand.
Meanwhile, a Department of Energy report stated the impact of DST was a savings of only 0.03% of electricity consumption over the year 2007. It did not find any statistically significant changes in traffic volume or passenger vehicle gas consumption that could be due to extended Daylight Savings Time.
A 2018 meta-analysis of 44 studies found modest energy savings of 0.34 percent while DST was in effect, but results varied based on the data and methodologies applied.
Overall, the findings surrounding DST and energy costs are inconclusive, and contradictory.
Fewer traffic crashes
Supporters of permanent Daylight Savings Time argue an extra hour of sunlight in the afternoon will reduce the number of traffic accidents. However, existing research points to the opposite.
A 1996 Canadian study found that DST and losing an hour of sleep resulted in an 8% increase in traffic accidents on average, while the switch back an hour in the fall decreased the number of accidents by roughly the same amount.
A U.S. study in Sleep Medicine found that sleep deprivation on the first Monday after the switch to Daylight Savings Time resulted in a small rise in deadly accidents.
Similarly, a 2020 review in Current Biology observed an increase in the number of accidents due to sleepy drivers in the first week of DST. The review concluded:
“In general, accidents are most likely to occur in the morning hours (between 6am and 8am), which has also been attributed to higher levels of driver sleepiness in the first half of the day than in the latter half of the day during any week of the year. This phenomenon appears to be acutely aggravated by DST transition. The absence of a similarly increased MVA risk in the week after DST further indicates that the illumination conditions play a contributing, but minor role. Analyses of the fall transition back to ST further support this interpretation.”
Reduced crime
Based on the current evidence available, one of the only factors that might benefit from a move to permanent DST is a reduction in crime.
One study published in The Review of Economics and Statistics found a 7% drop in robbery after a shift to DST. The effects were largest during the hours directly affected by the shift in daylight. The researchers estimated $59 million in annual social cost savings from the avoided robberies.
Congress should follow the science
To date, the American Academy of Sleep Medicine and more than 20 medical, civic, and professional organizations have endorsed a return to Permanent Standard Time.
While “darkness kills, sunshine saves” is a clever catchphrase, we encourage lawmakers to dig deeper into the research and acknowledge what the evidence shows, before casting a vote.