The clock moves back an hour when daylight saving time ends

(AP) – Good news: You’ll get a glorious extra hour of sleep. The Bad: Over the next few months, the United States will be as dark as nightfall.

Daylight saving time ends at 2am local time on Sunday, meaning you should set your clocks back an hour before going to bed. Standard Time will continue until March 9, when we will “jump forward” again with the return of Daylight Saving Time.

Spring changes can be harder on your body. Dark mornings and light evenings can throw off your internal body clock, making it harder for you to fall asleep on time for weeks or longer. Research even found an increase in heart attacks and strokes immediately after the March time change.

“Retreating” should be easier. But changing your sleep habits can still take some time, not to mention the negative consequences associated with 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, may also experience difficulties.

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

Most countries do not observe daylight saving time. For those that do – mainly in Europe and North America – the date for the clock change varies.

Two states – Arizona and Hawaii – do not change and maintain 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 triggered by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we become more alert. Patterns change as we age, which is one reason why early risers turn into teenagers who are difficult to wake up.

The morning light resets the rhythm. In the evening, levels of the hormone melatonin begin to rise, causing sleepiness. Too much light in the evening—an extra hour compared to daylight saving time—delays this surge and the cycle becomes out of sync.

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

How do time changes affect sleep?

Even changing clock times can disrupt your sleep schedule—because even though the clocks change, your work and school start times stay the same.

This is a problem because so many people are already sleep deprived. About one in three adults in the United States sleeps less than the recommended seven-plus hours per night, and more than half of U.S. teens do not get the recommended eight-plus hours of sleep on weekdays.

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

Will the US ever be able to get rid of the time change?

From time to time, legislators propose to abandon the time change altogether. The most prominent recent effort, a now-stalled bipartisan bill called the Sunshine Protection Act, proposes making daylight saving time permanent. Health experts say lawmakers did the opposite: Standard time should be made permanent.

Dairy farmer Aubrey Jarrell of Kentwood, Louisiana, isn’t a fan of changing times. He said it interferes with his cows’ strict milking schedule and causes them stress, “and stress is not good for a dairy cow.” Milk production will continue to decline until they adjust, he said.

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

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