From Journal of Clinical Sleep Medicine

Daylight saving time: an American Academy of Sleep Medicine position statement

The last several years have seen intense debate about the issue of transitioning between standard and daylight saving time. In the United States, the annual advance to daylight saving time in spring, and fall back to standard time in autumn, is required by law (although some exceptions are allowed under the statute). An abundance of accumulated evidence indicates that the acute transition from standard time to daylight saving time incurs significant public health and safety risks, including increased risk of adverse cardiovascular events, mood disorders, and motor vehicle crashes. Although chronic effects of remaining in daylight saving time year-round have not been well studied, daylight saving time is less aligned with human circadian biology—which, due to the impacts of the delayed natural light/dark cycle on human activity, could result in circadian misalignment, which has been associated in some studies with increased cardiovascular disease risk, metabolic syndrome and other health risks. It is, therefore, the position of the American Academy of Sleep Medicine that these seasonal time changes should be abolished in favor of a fixed, national, year-round standard time.

CITATION:

Rishi MA, Ahmed O, Barrantes Perez JH, et al. Daylight saving time: an American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2020;16(10):1781–1784.

Acute effects of switching between standard time and DST

Shifting from standard time to DST has been associated with increased cardiovascular morbidity, including risk of myocardial infarction,^7,8 stroke,⁹ and hospital admissions due to the occurrence of acute atrial fibrillation.¹⁰ An increase in missed medical appointments and increased emergency room visits and return visits to the hospital are also seen only during the spring transition from standard time to DST.^11,12 The one-hour time shift in the spring results in less exposure to light in the morning and greater exposure to evening light. In the presence of continuing social or occupational demands in early morning hours, this delay results in sleep loss and resultant sleep debt,¹³ in addition to circadian misalignment.² The end result is a variety of cellular derangements, including altered myocyte gene expression,¹⁴ altered epigenetic and transcriptional profile of core clock genes,¹⁵ increased production of inflammatory markers,¹⁶ lower vagal tone resulting in higher heart rate and blood pressure, and reduced sleep.¹⁷

Although most acute health-related effects are noted only when transitioning from standard time to DST, transitions both into and out of DST have been associated with sleep disruption,¹³ mood disturbances and suicide.¹⁸ Traffic accidents increase in the first few days after the change from standard time to DST,¹⁹ with an increase in fatal crashes of up to 6% in the United States.²⁰

On the Monday after the transition to DST, volatility in stock markets in the U.S. has been observed.²¹ While reasons for this are not entirely clear, proposed mechanisms include the impact of sleep deprivation on frontal lobe functioning, which may result in impaired judgement and decision-making capacity.²²

Chronic effects of DST

There is little direct evidence regarding the chronic effects of DST. Most studies have either been retrospective or have addressed the issue indirectly. DST has been associated with a decrease in crime rate,²³ and it may be associated with a modest overall decrease in risk of motor vehicle crashes, possibly due to hours of daylight lasting longer in the evening when most accidents occur, along with other, less obvious reasons.⁵ However, when temporary, year-round DST was adopted in response to an Organization of the Petroleum Exporting Countries (OPEC) oil embargo, increased fatalities among school-aged children in the morning were noted between January and April. These findings may be due to darkness lasting longer in the morning when children are traveling to school, while other factors also may be at play.²⁴

DST is less well-aligned with intrinsic human circadian physiology, and it disrupts the natural seasonal adjustment of the human clock due to the effect of late-evening light on the circadian rhythm.²⁵ DST results in more darkness in the morning hours, and more light in the evening hours. Both early morning darkness and light in the evening have a similar effect on circadian phase, causing the endogenous rhythm to shift to later in the day. There is evidence that the body clock does not adjust to DST even after several months.²⁶ Permanent DST could therefore result in permanent phase delay, a condition that can also lead to a perpetual discrepancy between the innate biological clock and the extrinsic environmental clock, as well as chronic sleep loss due to early morning social demands that truncate the opportunity to sleep. The chronic misalignment between the timing of demands of work, school, or other obligations against the innate circadian rhythm is called “social jet lag.”²⁷ Studies show that social jet lag is associated with an increased risk of obesity,²⁸ metabolic syndrome,²⁹cardiovascular disease,³⁰ and depression.³¹ One study found that in the fall, during the shift from DST back to standard time, there was a reduction in the rate of cardiovascular events,⁷suggesting that the risk of myocardial infarction may be elevated because of chronic effects of DST.³² Social jet lag associated with DST may be worse in the western-most areas within a given time zone, where sunset occurs at a later clock time.³³ Adopting permanent DST also would undo the benefits of delaying start times for middle schools and high schools.³⁴

During the 1973 OPEC oil embargo, minimal, if any, of the purported energy savings were actually observed in the U.S., and the policy was highly unpopular,³⁵ especially in rural areas of the U.S. After a single winter, the policy was reversed by an overwhelming congressional majority. The unpopularity of the act was likely because, despite greater evening light, the policy resulted in a greater proportion of days that required waking up on dark mornings, particularly in the winter.

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