After daylight savings time ends, the hands of the clocks go back one hour

(AP) – The good news: You’ll get a great extra hour of sleep. The Bad: Late nights will be pitch black in the US for the next few months

Daylight saving time ends at 2 a.m. local time on Sunday, which means you should turn your clocks back an hour before going to bed. Standard time will continue until March 9th, when we will “jump” back to daylight saving time again.

This spring time change can be more difficult on your body. Darker mornings and lighter evenings can throw off your internal body clock, making it harder for you to fall asleep on time for weeks or longer. Studies have even found a spike in heart attacks and strokes immediately after the March time change.

“Backing off” should be easier. But it can still take some time to adjust your sleep habits, not to mention the downsides of leaving work in the dark or trying to exercise while there’s still plenty of light. Some people with seasonal affective disorder, a type of depression typically associated with shorter days and less sunlight in the fall and winter, can also have a hard time.

Some health groups, including the American Medical Association and the American Academy of Sleep Medicine, have said it’s time to ditch the time switches and that standard time is better aligned with the sun and human biology.

Most countries do not observe summer time. For those that do—mostly in Europe and North America—the clocks change date varies.

Two states – Arizona and Hawaii – do not change and remain on standard time.

Here’s what you need to know about the twice-yearly ritual.

How the body reacts to light

The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we are more alert. Patterns change with age, one reason early risers turn into hard-to-wake teenagers.

The morning light resets the rhythm. By evening, the level of the hormone melatonin begins to rise sharply, causing drowsiness. Too much light in the evening—that extra hour after daylight saving time—delays that surge and throws the cycle out of sync.

And this circadian clock affects not only sleep, but also heart rate, blood pressure, stress hormones, and metabolism.

How does time change affect sleep?

Even changing the time on the clock can disrupt sleep schedules, because even if the clocks change, the start time for work and study remains the same.

This is a problem because many people are already sleep deprived. About 1 in 3 American adults sleep less than the recommended seven-and-a-half hours a night, and more than half of U.S. teenagers don’t get the recommended eight-and-a-half hours on a weekday.

Sleep deprivation is linked to heart disease, cognitive decline, obesity, and numerous other problems.

Will the US ever get rid of the time change?

Legislators from time to time propose to get rid of time shifting altogether. The most notable latest effort, a bipartisan bill called the Sunlight Protection Act, which has now stalled, proposes to make daylight saving time permanent. Health experts say lawmakers have backtracked – the standard time should be made permanent.

Milkman Aubrey Jarrell of Kentwood, Louisiana, is not a fan of the time change. He said it interfered with the rigorous milking routine of his cows and caused them stress, “and stress is not good for a dairy cow.” According to him, there is a drop in milk production until they adjust.

“Keep the time constant—whatever it is—but keep it constant,” he said.

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The Associated Press Department of Health and Science receives support from the Howard Hughes Medical Institute Science and Education Media Group. AP is solely responsible for all content.