Taking to “heart” the proposed legislation for permanent daylight saving time

Abstract

In March 2022, the US Senate passed the Sunshine Protection Act that would abolish the biannual change in clocks each fall and spring and permanently adopt daylight saving time that aligns with the “spring forward” time change each March. A number of scientific and medical societies have endorsed the abolishment of the biannual clock change, but oppose the permanent adoption of daylight saving time. Instead, leading organizations such as the American Academy of Sleep Medicine (AASM) and the Society for Research on Biological Rhythms (SRBR) position statements highlight peer-reviewed evidence in favor of a permanent shift to standard time. The present perspectives will summarize some of the key AASM and SRBR recommendations, with a particular focus on the potential cardiovascular implications of a legislative change that would result in a permanent switch to either standard time or daylight saving time. Collectively, although there is building scientific consensus that abolishing the biannual time change has several sleep and circadian health benefits, the preponderance of evidence is opposite to the current legislation and instead suggests a permanent switch to standard time may offer the maximum health and safety benefits. This scientific evidence should be considered as the United States House of Representatives considers the Sunshine Protection Act.

INTRODUCTION

On March 15, 2022, the US Senate passed the Sunshine Protection Act that aims to make daylight saving time permanent. For years there have been rigorous debates on the value and benefits of the biannual 1-h clock change in the fall and spring, with strong opinions on the following three options: 1) maintain the biannual change in time, 2) permanently convert to standard time, or 3) permanently convert to daylight saving time. In recent weeks, there has been a strong public reaction to the Sunshine Protection Act, with both positive and negative feedback. Several medical and scientific societies have expressed concerns that the bill was passed during a consent agenda without rigorous debate. Two notable critics have been the American Academy of Sleep Medicine (AASM), the accrediting body for sleep medicine facilities in the United States and a society that focuses on both sleep and circadian disorders, and the Society for Research on Biological Rhythms (SRBR), which includes scientists with expertise in biological rhythms. Both AASM and SRBR have published position statements recommending the opposite action taken by the US Senate—a permanent switch to standard time (1, 2).

In the present perspective, we aim to summarize some of the key AASM and SRBR recommendations (1, 2), with a particular focus on the potential cardiovascular implications of the sudden biannual time change. We will also discuss the potential implications of a permanent switch to either standard time or daylight saving time. Cardiovascular disease remains a leading cause of death in the United States and around the globe, and our goal with this perspective is to highlight key scientific evidence that will inform the public and elected officials in the coming months as the House of Representatives considers taking up the Sunshine Protection Act.

STANDARD TIME VERSUS DAYLIGHT SAVING TIME

Although most Americans recognize and physically feel the impact of the biannual time change (with notable exceptions such as Arizona and Hawaii that opted out of daylight saving time in the 1960s), the definitions of standard time versus daylight saving time are often incompletely understood and should be clarified.

Standard Time

The period between fall and spring when clocks in most states are reset 1 h backward at 2:00 AM on the first Sunday of November. This “fall back” is often associated with an acute increase of sleep and circadian disruption.

Daylight Saving Time

The period between spring and fall when clocks in most states are set 1 h forward at 2:00 AM on the second Sunday of March. This “spring forward” is often associated with an acute loss of sleep and circadian disruption.

IMPACT OF BIANNUAL TIME CHANGE

In 2019 to 2020, two groups of leading physicians and scientists within sleep and circadian medicine published independent position statements highlighting evidence that the transition from standard time to daylight saving time (and sometimes the transition from daylight saving time to standard time) can be associated with health and safety risks (1, 2). Based on the presented evidence, the position statements concluded that the biannual time change was disruptive to sleep and circadian rhythms that contribute to overall health and quality of life and recommended a permanent switch to standard time, opposite to what was recently passed by the US Senate. Given the lack of rigorous congressional debate before the Senate consent vote, many House of Representative members (including members of both the Republican and Democratic parties) have called for more discussion around the merits of a permanent move to either standard time or daylight saving time.

The AASM and SRBR position statements outline a number of adverse health and safety concerns associated with the biannual time change. For example, the acute loss of sleep when shifting from standard time to daylight saving time each spring has been associated with increased traffic accidents (3, 4) and suicide (5). Although these associations should not be inferred as causal, there are randomized, controlled studies that demonstrate experimental sleep loss elicits increased human error during driving simulation (6, 7) and increased suicidal thoughts and ideation (8). Collectively, there is appropriate concern regarding the arbitrary, annual 1-h time change that society has self-imposed.

Although the issues around traffic safety, mood, and suicide are highly relevant to public health and safety, the readers of Am J Physiol-Heart and Circ Physiol are likely to be the most scientifically interested in the relationships between the biannual time change and adverse cardiovascular events. Specifically, the spring shift from standard time to daylight saving time has been associated with an increased risk of myocardial infarction (9, 10), stroke (11), and hospital admissions attributed to atrial fibrillation (12). Although most studies report a lack of relationship between myocardial infarction and the fall time change, one study reported a reduction of myocardial infarctions during the shift from daylight saving time to standard time when there is often an acute gain of sleep (13). Once again, although it is important to not overinterpret these associative findings, there are numerous well-controlled experimental studies demonstrating the adverse impact of experimental sleep loss on cardiovascular health, including several notable studies published in the Am J Physiol-Heart and Circ Physiol in recent years (14–22). Although the exact mechanisms remain uncertain, sympathoexcitation associated with sleep and circadian disruptions is one suspected mechanism (16). Indeed, it has been demonstrated that sleep loss combined with circadian misalignment significantly increased 24-h urinary norepinephrine (NE), with the most significant increases of urinary NE during the early morning hours when adverse cardiovascular events (i.e., myocardial infarctions) occur at the highest rates during a 24-h cycle (23).

It is important to note that although most of the adverse cardiovascular events associated with the biannual time change seem to be associated with the switch from standard time to daylight saving time, there is some evidence that the fall time change from daylight saving time to standard time might also be detrimental. Specifically, stroke rates are increased during both the fall and spring time changes (24). Another study reported a significant increase in thrombolysis treatments during both the fall and spring time changes, including both the day of the changes and the week after the time change (25). These findings suggests that the circadian misalignment may contribute importantly, and perhaps independently, to the sleep loss typically associated with the spring change from standard time to daylight saving time.

PERMANENT STANDARD TIME VERSUS PERMANENT DAYLIGHT SAVING TIME

The evidence described earlier clearly supports the elimination of the biannual time change. However, the question of selecting permanent standard time or daylight saving time remains. The difference between the two is simply more light in the morning or more light in the late afternoon/evening. Morning light plays a critical role in synchronizing our internal clocks and daylight saving time leads to a misalignment between our social clocks (i.e., the clocks on the wall) and our internal clocks, which are synchronized to the sun. Misalignment between internal clocks and the external world, including behavior, has been associated with impaired health (2). Last, it should not be underestimated the potential ramifications, a permanent switch to daylight saving time would have on children and adolescents. For years, sleep and circadian experts have advocated for later school start times for K-12 education, because later start times can improve mood and academic performance, and reduce adverse behaviors (26). Morning light exposure has antidepressant effects (27) and permanent switch to daylight saving time would mean there would be certain parts of the United States where it would be dark/dusk until nearly 9:30 AM in some states on the westernmost edges of various time zones, leading to hours of wakefulness and school without natural light exposure in the morning.

Conclusions

The AASM and SRBR position statements provide compelling evidence from peer-reviewed studies that should be carefully weighed as the Sunshine Protection Act is being considered by the House of Representatives. We applaud the US Senate for bringing this issue to the nation’s full attention and agree that the biannual time change is disruptive and problematic on a number of levels. Although there are many factors that our elected officials need to consider, including economic implications of any change, those factors need to be discussed and debated against public health and safety risks. The AASM remains the authoritative body for sleep medicine in the United States, and the SRBR is the authority on biological rhythms, so unless there is compelling evidence against the AASM and SRBR position statements (1, 2), we recommend the House of Representatives consider the opposite perspective—a permanent switch to standard time. We remain hopeful that there will be a healthy discourse of discussion and debate that our Republic is founded on—let’s get this one right.

GRANTS

This work was supported by National Institutes of Health Office of Extramural Research Grant AA-024892 (to J.R.C.).

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

AUTHOR CONTRIBUTIONS

J.R.C. conceived and designed research; J.R.C., K.L.K., and B.M. interpreted results of experiments; J.R.C. drafted manuscript; J.R.C., K.L.K., and B.M. edited and revised manuscript; J.R.C., K.L.K., and B.M. approved final version of manuscript.