Everything you need to know about daylight saving time

In the early hours of Sunday, Nov. 2, clocks went back one hour as a result of the end of daylight saving time. However, despite the apparent advantage of being able to rest 60 minutes more a day, do you know what the time change means for our body? Does every state apply it? Since when has it been done and why? In this article we tell you everything you need to know about a measure in the spotlight of experts.

At 2 a.m. on Sunday, the clocks of almost all citizens went back to 1 a.m. as a result of the end of daylight saving time. This is a measure that seeks to optimize the use of sunlight after the summer. It won't be until  March 8, 2026 when the clocks will go back to slowing down by one hour.

Although on paper it all sounds very nice, this is a measure that is receiving increasing debate around the world, with multiple countries studying its elimination in the near future due to the disadvantages pointed out by experts.

What does the end of daylight saving time mean for our bodies?

Besides the obvious possibility of resting an extra hour during the night of the change, our body suffers repercussions as a consequence of the double time change during the year. Several health-related groups, such as the American Medical Association and the American Academy of Sleep Medicine, have long called for standard time to remain the same year-round.

New research from Stanford University reinforces this conclusion and points out that switching from one schedule to another is the worst option for our health. According to the study, keeping either schedule immovable would be healthier, although keeping the permanent standard schedule fixed would be somewhat better, since it "more closely matches the sun and human biology," the so-called circadian rhythm.

"The best way to look at it is as if the central clock were the conductor of an orchestra and each of the organs were a different instrument," explained to LA Times Jamie Zeitzer, co-director of Stanford's Center for Sleep and Circadian Sciences.

"More light in the morning and less at night is the key to keeping that rhythm on schedule, with all the instruments in harmony." If the clock is disturbed on a regular basis by time changes or other reasons, "each of the body's organ systems, such as the immune system or metabolism, simply works a little less well," the expert notes.

How does light affect our body?

The human brain has an internal clock that adjusts according to exposure to sunlight and darkness. This is the circadian rhythm, which has a cycle of about 24 hours and determines when we get sleepy and when we are more alert. However, this cycle varies according to age and body changes. That is, it is one of the reasons why the inexhaustible and early risers become sleepy teenagers for whom getting out of bed is a daily everest.

Morning light is responsible for restoring the rhythm. The secretion of melatonin increases in the dark, causing drowsiness. Therefore, too much light at night, whether from natural light, artificial light, or even exposure to screens delays the rise in levels of this hormone in the body and breaks the cycle.

The consequences go beyond the mere alteration of sleep, since the circadian rhythm also influences heart rate, blood pressure, stress hormones and metabolism.

In fact, several studies have found that sleep problems are the cause of more traffic accidents, higher risk of diabetes and even a higher risk of heart attacks. This would be the consequence of a prolonged absence of sleep, which goes beyond the simple feeling of grogginess. Among other things, it can desynchronize the connection between the body's internal clock and the sun, something that is especially common among shift workers.

Do all states change their clocks?

The vast majority of states follow the Uniform Time Act, passed in 1966, which imposed standard time across the country within established time zones. Under this standard, all clocks go forward one hour at 2 a.m. on the last Sunday in April and backward one hour at 2 a.m. on the first Sunday in November.

However, two states make use of their power not to touch citizens' clocks throughout the year. They are Arizona and Hawaii. Indiana was part of this group until 2006, when state laws changed. In addition, Puerto Rico, the U.S. Virgin Islands, American Samoa and Guam also keep the time unchanged.

Why is time changed twice in the U.S.?

The origin of its application in the USA of the two time changes has its origin in the 1970s. To be exact, in 1973, due to the oil embargo of that year. In the interest of saving energy, Congress enacted a year-round trial period of daylight saving time from January 1974 to April 1975.

Franklin, 'original promoter' of daylight saving time

Although its implementation would come much later, it was one of the founding fathers, Benjamin Franklin, who was one of the pioneers in the proposal to adjust the time throughout the year to reduce the consumption of candles by taking advantage of sunlight.

In a 1784 essay, Franklin wrote that "going to bed early and rising early makes a man healthy, wealthy and wise", which can be seen as a scathing criticism or a wake-up call.

Where there is no longer any doubt of intent is in the campaign of the British William Willett in 1905. Willett noticed that many of his fellow citizens slept through sunny mornings and began a campaign seeking to introduce the time change.

The U.S. began adjusting its clock in 1918 and to this day it is a very controversial issue.