Is Daylight Saving Time Bad For Your Health?

Those long summer evenings are not good for your health, according to a new statement published in the Journal of Clinical Sleep Medicine.

Nearly two dozen physicians and researchers from the American Academy of Sleep Medicine are calling for an end to daylight saving time, the period of time from March through October when clocks “spring forward.” Instead, the authors—members of the Academy’s 2019-2020 Public Safety Committee and Board of Directors—are calling for permanent standard time. The statement has been endorsed by 20 associations, including the World Sleep Society.

The statement authors argue that standard time is more in line with the circadian rhythm, the body’s internal clock that helps regulate the sleep-wake cycle.

“We all have an internal clock, and our body depends on its functioning to work normally,” lead author Muhammad Adeel Rishi, MD, tells Verywell. Rishi is a pulmonology, sleep medicine, and critical care specialist at the Mayo Clinic Health System in Eau Claire, Wisconsin. “That internal clock is very closely connected to the photoperiod or the sun cycle — how much light exposure we get, and it changes throughout the year [as Earth rotates around the Sun]. Those connections have been there for a very long time, and any artificial constructions cause health risks. Daylight saving time is an artificial construct, and we’re beginning to understand how it’s been impacting our health.”

How Time Change Affects the Body

Time as we know it is a relatively recent construct. For most of human history, people have woken, worked, and slept according to the sun, and for good reason: Light is a powerful cue for the regulation of the body’s internal circadian rhythm.

Daylight saving time interferes with the natural seasonal adjustment of the human clock because of both morning darkness and evening light, the authors write.

“The acute alterations in timing due to transitions to and from DST contribute to misalignment between the circadian biological clock and the light/dark cycle (or photoperiod), resulting in not only acute personal disruptions but significant public health and safety risks,” the authors write.

In other words, by adjusting the light/dark cycle, DST is interfering with the body’s natural sleep and wake cycle—and it’s putting their health at risk.

“[Our circadian rhythm] schedules everything from your mood to the hormones that are secreted in the body to when you get sleepy and when you wake up,” Rishi says.

“The system evolved over millennia where our internal clock got closely connected to when the sun goes up and when the sun goes down. Any destruction of that connection causes health effects.”

Health Risks Associated with Time Change

The switch from standard to daylight saving time has been associated with increases of a number of acute health risks on the body, including:

• Cardiovascular morbidity
• Myocardial infarction
• Stroke
• Hospital admissions (due to the occurrence of acute atrial fibrillation)

“The acute [changes] take about a week, but there’s emerging evidence that the body might not completely adjust to change for the duration of while people are on daylight saving time,” Rishi says, adding additional research is needed to study long-term consequences of time change.

Researchers have found that any time change has been associated with sleep disruption, mood disturbances, and suicide. A prolonged misalignment of circadian rhythm is associated with an increased risk of obesity, metabolic syndrome, cardiovascular disease, and depressions, the authors write.

Rishi expresses concern over the misalignment because the circadian rhythm has been repeatedly strained over the last century with the advent of electricity, televisions, computers, smartphones, tablets, and other distractions that allow people to stay up later and interfere with the body’s natural sleep process.

“That pressure has never been more intense on your circadian biology. You have that connection that’s already severely stressed and then in March, boom, you put another hour on it,” he says. “You have more accidents, more myocardial infarctions, and there’s now more evidence people are going to the ER. Another paper published at the AASM meeting showed increased medical mistakes.”

Still, Rishi says not everyone will be affected to the same degree.

"Some people are certainly more vulnerable than others," he says. "A good example would be a night owl—a person whose internal clock is naturally delayed—who has to get up early every day to go to work. Once daylight saving time hits, this person, who was already working against their natural circadian rhythm, is put under extra strain and is more likely to have problems."

History of Time Change

Many people likely don’t question the seasonal time change, and there’s a common misconception about daylight saving time: that the extra hour of daylight is for farmers, a carryover from agrarian society still practiced in modern life. But when the legislation was introduced in the 20th century, many farmers protested the time change because it meant doing more of their morning work in the dark.

During World War I, in an effort to conserve fuel to produce electricity, Germany and Austria adopted daylight saving time. Many other European countries followed suit. The United States adopted the practice as part of the Standard Time Act of 1918, which also established the time zones. Adoption of daylight saving time varied following the end of World War I.

In the United States, daylight saving time was made law as part of the Advancement of Time or Changeover Dates Act of 1973. Congress extended the duration of DST through the Energy Policy Act of 2005. It is observed starting at 2 a.m. the second Sunday in March and ends at 2 a.m. the first Sunday in November.

A Call for Change

Daylight saving time continues to be observed, largely by countries in North America and Europe.

But in March 2019, the European Union voted to end the mandatory switch to daylight saving time by 2021. That vote serves as a basis for discussions with European Union countries to determine a final law.

In the United States, federal law requires adherence to daylight saving time, but states can be granted approval to opt out. Hawaii and parts of Arizona are exempt from daylight saving time along with territories Puerto Rico, American Samoa, Guam, and the Virgin Islands. Several legislators at the state and federal level have introduced legislation to eliminate spring and fall time changes, either for the permanent adoption of daylight saving or standard time.

In July, an American Association of Sleep Medicine survey of more than 2,000 U.S. adults found that 63% support the elimination of seasonal time changes in favor of a national, fixed, year-round time, and 11% oppose it.

“I think a lot of people don’t like seasonal time switches because in terms of their daily life, people feel it,” Rishi says.