Daylight Saving Time

The American Academy of Sleep Medicine supports the elimination of daylight saving time. 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.

AASM Daylight Saving Time Position

In October 2020, the American Academy of Sleep Medicine published a daylight saving time position statement. The statement was endorsed by more than 20 medical, scientific, and civic organizations.

What is the AASM position on daylight saving time?

It is the position of the AASM that the U.S. should eliminate seasonal time changes in favor of a national, fixed, year-round time. Current evidence best supports the adoption of year-round standard time, which aligns best with human circadian biology and provides distinct benefits for public health and safety.

What are the negative health and safety effects of daylight saving time changes?

The annual change from standard time to daylight saving time is associated with increased risk of heart attacks and stroke. There are increased hospital admissions due to atrial fibrillation. There also is an increase in emergency room visits and missed medical appointments. Traffic accidents increase in the first few days after the change from standard time to daylight saving time. The spring and fall time changes also have been associated with mood disturbances and suicide.

How do daylight saving time changes affect our sleep?

During daylight saving time, we tend to go to bed and fall asleep later at night, resulting in sleep loss. The spring and fall time changes also can disrupt our sleep schedule and have a negative effect on the quality of our sleep. The daylight saving time changes can be especially problematic for any populations that already experience chronic insufficient sleep or other sleep difficulties. Populations at greatest risk include teenagers, who tend to experience chronic sleep restriction during the school week, and night shift workers, who often struggle to sleep well during daytime hours.

Why is daylight saving time bad for our sleep?

Light and darkness are the most powerful timing cues for alertness and sleepiness in the human body. We are more alert in the daytime when there is bright sunlight, and we are sleepier at night when there is darkness. Our daily sleep/wake rhythm closely follows the 24-hour light/dark cycle. This is called our “circadian rhythm.” The one-hour time shift during daylight saving time results in less exposure to light in the morning and greater exposure to evening light. As a result, we tend to go to bed and fall asleep later, resulting in chronic sleep loss. Daylight saving time causes ongoing misalignment between our sleep/wake rhythm and the light/dark cycle, also called “social jet lag.”

Why is standard time better for our sleep than daylight saving time?

Standard time is best aligned with human circadian biology. During standard time, your body clock, the timing of sunrise and sunset, and local clock time are more in sync than during daylight saving time. This alignment enables most people to sleep better at night and feel more alert during the day.

Is daylight saving time like jet lag?

No, daylight saving time and jet lag are different. Jet leg, caused by a change in time zone, involves a temporary mismatch between your body clock and the local clock time. It is temporary because the timing of sunrise and sunset in your new time zone is different from your old time zone; the sun rises and sets earlier or later than in your previous location. Therefore, your body is able to adjust to the local clock time because of the light cues provided by the sun. In contrast, during daylight saving time, the local clock time changes, but the timing of sunrise and sunset remains the same. This causes ongoing misalignment between your body clock, the sun time, and local clock time.

Does daylight saving time give us more sunlight?

There are common misconceptions about daylight saving time and standard time. People often like the idea of daylight saving time because they think it provides more light. (People often equate daylight saving time with “summer time.”) In the same way, people may dislike the concept of standard time because they think it provides more darkness. (They equate standard time with “winter time.”) The reality is that neither one provides more light or darkness than the other; it is only the timing of light and darkness th