Daylight saving time (DST) is when clocks are moved one hour later on the second Sunday in March at 2 am so that the sun rises later in the morning and sets later in the evening. This is referred to as "springing forward." On the first Sunday in November at 2 am it switches back, which is referred to as "falling back."

There are many different arguments for and against DST, but sleep scientists don't support changing the time. Dr. Christopher Barnes, Associate Professor of Management at the University of Washington who researches the impact of sleep deprivation says, "When we change the time by one hour, it throws a monkey wrench into our circadian process. The following Monday, we've discovered that people have about 40 minutes less sleep. Because we're already short on sleep to begin with, the effects of even 40 minutes are noticeable."

One of the pillars of good sleep hygiene is to fall asleep and wake up at the same time every night (including weekends). Your brain's internal clock is set by its exposure to sunlight, which is your circadian rhythm. When you change the time when you regularly go to sleep and wake up, your brain's expectation for when to fall asleep and wake up is altered. Research has confirmed that DST causes people to be sleep deprived.

A study published by the National Institutes of Health combined surveys from 55,000 people in Europe on their sleeping and wakefulness for 8 weeks around DST in the spring and reverting back in the fall. The research showed that people never fully adjust their circadian rhythm to the time change, and the time change is more difficult for night owls (people who go to bed late). A smaller study involving 9 volunteers referred to by LiveScience concluded that the fall transition was more difficult for larks (early risers).

A 2016 study published by the American Academy of Neurology found that the rates for stroke were 8% higher in the 2 days after DST. Cancer patients were 25% more likely to have a stroke after daylight saving time than during another period. The risk was also higher for those over age 65, who were 20% more likely to have a stroke right after the transition.

According to the University of Alabama at Birmingham, “The Monday and Tuesday after moving the clocks ahead one hour in March is associated with a 10% increase in the risk of having a heart attack,” says UAB Associate Professor Martin Young, Ph.D., in the Division of Cardiovascular Disease. “The opposite is true when falling back in October. This risk decreases by about 10%.”

A study published in Sleep Medicine found that fatal car accidents rise significantly on the Monday after the spring shift and the Sunday of the fall shift. The researchers claim that "The behavioral adaptation anticipating the longer day on Sunday of the shift from DST in the fall leads to an increased number of accidents suggesting an increase in late-night (early Sunday morning) driving when traffic-related fatalities are high, possibly related to alcohol consumption and driving while sleepy." They further explain, "Public health educators should probably consider issuing warnings both about the effects of sleep loss in the spring shift and possible behaviors such as staying out later, particularly when consuming alcohol in the fall shift. Sleep clinicians should be aware that health consequences from forced changes in the circadian patterns resulting from DST come not only from physiological adjustments but also from behavioral responses to forced circadian changes."

According to the American Psychological Association, mineworkers who have slept on average 40 minutes less due to the time change experience 5.7% more workplace injuries in the week after DST than any other week of the year. This is because moderate sleep deprivation can cause cognitive and coordination impairment that is worse than being legally drunk.

Dr. Kyoungmin Cho of the University of Washington, along with Dr Barnes, published a study cited on the Association for Psychological Science site that judges even give harsher sentences on the Monday after the DST switch. This is consistent with what research has already told us about being sleep-deprived: people have less control over their emotions, are more impulsive, and have a harder time making decisions.

Benjamin Franklin is the originator of this practice as he thought it would conserve energy because people wouldn't need to light their homes because they could use sunlight.

However, the history of its use is spotty and inconsistent. The United States used it during WWI to conserve fuel, then it was abolished, before being used again in WWII. After WWII, it was chaotically used in some places and not in others. St. Paul Minnesota and Minneapolis Minnesota were at different times. In 1966, Congress enacted the Uniform Time Act which required that states could decide what they wanted to do, but the entire state had to be on the same clock.

Currently, in the United States every state observes DST except for Hawaii and Arizona (although the Navajo Nation in Arizona does observe it).

Most of Europe observes DST, including the United Kingdom. Australia, New Zealand, South America set their clocks forward in the fall and move them back in the spring. Russia doesn't observe it.

There are several things you can do to prepare yourself for an upcoming DST switch or the reversion back to non-DST time:

1. If you're moving the clocks forward, take a 15-20 nap in the afternoon on the day before, and the day after if you feel you could use it.
2. The night that you're moving the clocks forward, use a natural sleep aid or eat foods that help facilitate an earlier onset of sleep and deeper sleep.
3. For a week or two leading up to a time change, gradually add or subtract a few minutes to your bedtime to make the acclimation less difficult on the day of the change.
4. The morning after "springing forward" expose yourself to sunlight in the morning, and if possible, exercise early (and outside is better).