It’s that time of year again when the days are getting shorter and the clocks are moved back. While many of us may consider the biannual time change to be a quirky but largely innocuous event, evidence suggests that it’s harming our health in surprising ways. Accordingly, a wave of recent legislation—both nationally and internationally—has pushed towards eliminating the biannual clock change and therefore remaining on one schedule year-round.
Every year, we change our clocks one hour forward in the spring (springing forward) and one hour back in fall (falling back). The idea is to better align the clock time with daylight: as the sun begins to set later in the spring, the clocks are moved forward to reflect the longer days (daylight saving time (DST) or “summer time”). The clocks are then turned back to “standard time” in the fall as the days become shorter. However, almost half of US states have passed bills to eliminate the biannual clock change and stay on either DST or standard time year-round (although because changing our clocks stems from federal law, Congress must approve the bills and has yet to do so). On the federal level, the 2021 Sunshine Protection Act—reintroduced after a failed 2018 attempt—would mandate a permanent DST in the country. Despite remaining in committee, the bill has received bipartisan support, which may reflect growing momentum to abandon this somewhat outdated and unexpectedly harmful practice.
However, almost half of US states have passed bills to eliminate the biannual clock change and stay on either DST or standard time year-round.
The idea of daylight saving dates back to Benjamin Franklin writing about “saving” daylight in 1784, but this was pre-electricity when candles were the primary source of light after sundown and it may have made sense to “save wax” during the light hours (he was also clearly joking). Daylight saving caught on during WWI and WWII to conserve fuel during the war and was instituted in 1966 with the Uniform Time Act, although individual states could and did opt out, including Hawaii, Arizona, and certain Indiana counties (cue West Wing episode).
The months of DST were extended in 2005 with the goal of conserving energy, but since we’re no longer living by candles like Ben, most energy these days goes into small appliances like TVs. So when there’s more daylight we may use less lighting and conserve some energy (Belzer et al., 2008), but we also use more electricity for things like heat and cooling (Kotchen & Grant, 2011). Overall, it seems that energy can be conserved in locations with milder temperatures farther from the equator, but more energy can actually be used during daylight in locations closer to the equator (Havranek et al., 2008).
While time zones are important, evidence suggests that it’s the act of changing the clock that causes problems, not necessarily the time itself. The most obvious consequence of the spring clock change is a lack of sleep, which can last more than a few days (Harrison 2013) and increase inflammation and stress hormones, leading to higher heart rate and blood pressure (Mullington et al., 2009). The spring transition to DST impacts adolescents’ vigilance in school (Medina et al., 2015) and SAT scores (Gaski & Sagarin, 2011), and is associated with higher incidence of acute myocardial infarction and ischemic stroke (Manfredini et al., 2019), workplace injury (Barnes & Wagner, 2009), accidental death (Coren 1996), fatal car crashes (Fritz et al., 2020), and aggression (Umbach et al., 2017). Judges give longer sentences (Cho et al., 2016), pregnant women who went through in vitro fertilization suffer more spontaneous pregnancy (Liu et al., 2017), and even genetic changes have have been found (Jagannath et al., 2017). Given these consequences, it might be time to #LocktheClock, as the kids are calling it.
But it’s still unclear why this is the case. Is it just lack of sleep and grogginess during the day? Some scientists argue that it’s disruptions to our circadian rhythm—our biological, internal clock—that make switching the clock particularly harmful. Neurons in our hypothalamus sync to the light-dark cycle of our environment and then pass along the message to the rest of the body (Klein et al., 1991). This entrainment process is different for different people, meaning that some of us naturally prefer waking up early while others prefer to stay up late. Historically, that individual variation was relatively small, since the synchronization of our neurons was linked to the cycle of the sun. In our post-industrial, electricity-illuminated world, however, our behavior is less dictated by nature, and the discrepancy between the natural cycle of the sun, our socially-imposed time, and our internal clock is getting more and more out of whack (Roenneberg et al., 2019)—aside from electricity itself (Falchi et al., 2011), Netflix (Komada et al., 2015) and Twitter (Heo et al., 2017) are not helping with their melatonin-inhibiting effects.
Some scientists argue that it’s disruptions to our circadian rhythm—our biological, internal clock—that make switching the clock particularly harmful.
This circadian misalignment is not trivial: it has been linked to several harmful effects (Baron & Reid, 2014), including higher risk of cardiovascular disease (Morris et al., 2016), insulin sensitivity (Eckel et al., 2015), and inflammatory markers and cytokine imbalance (Wright et al., 2015). When the clocks are changed twice a year, not only are we making ourselves drowsy, we’re uprooting the synchronization that our circadian rhythms have been working on for that half of the year. That might be why many of the harmful effects observed during the DST transition are exacerbated in the western-most regions of a time zone—the sun traverses the country from east to west, so eastern states are sunny earlier than western parts of the same time zone (think Maine vs. Michigan). When the clocks jump forward in the spring, the disparity is greatest in those regions where it was darker for longer, and it’s there that traffic accidents, for instance, increase the most (Fritz et al., 2020). Numerous studies have found that distance from the eastern edge of the time zone is associated with life expectancy (Borisenkov 2011), increases in cancer incidence (VoPham et al., 2018) and mortality (Borisenkov 2011), and even obesity, diabetes, cardiovascular disease, and per capita income (Giuntella & Mazzonna, 2019).
All is not lost, however! When people with later circadian cycles (the proverbial night owls) were exposed only to natural light, their circadian timing became more similar to early risers (Wright Jr. et al., 2013). This suggests that our behavior can be modified. Maybe you’ve had an experience where you’re in a cabin in the woods and naturally go to sleep and wake up earlier—perhaps partly because there’s less to do, but maybe also because it just feels more natural. Maybe we’re like the turtle hatchlings attracted to the artificial lights that lead them astray, but instead of being told again to stop scrolling before bed and pick up a book (although we really should), we might be able to naturally shift ourselves by spending more time outdoors in natural light. It’s important to mention that this suggestion reflects a certain amount of privilege, as access to nature and quality of outdoor space is heavily stratified by race and socioeconomic status (Schwarz et al., 2015). If access to natural light can have such measurable effects on health and mitigate circadian misalignment, even in part, then building and maintaining accessible green and outdoor spaces in those neighborhoods that need them most should be a top priority.
When the 1918 Standard Time Act established the time zones, people were vehemently opposed, saying that it felt wrong to follow “clock time” instead of “sun time”. Many scientists today are arguing the same thing. Some advocate for reassigning time zones based on alleviating the discrepancy between the socially-dictated and sun-dictated time (Roenneberg et al., 2019). Instead of imposing one time or the other, the European Union recently let its member states choose whether or not they wanted to stay permanently on DST (known there as “summer time”). Maybe we could also let states choose, alleviating biannual switching and the harms that go along with it. Sure, it might be annoying at first to get used to what basically amounts to new time zones, but is it more annoying than changing our clocks twice a year, and would it carry the same repercussions on our health and safety? And anyway, don’t most of us just google “time in Mexico City” when we’re trying to figure it out?
Written by Zoe Guttman
Edited by Yuki Hebner and Arielle Hogan.
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