The good news: you’ll get a good hour of extra sleep. The bad: It will be pitch black in the late afternoon for the next few months in the United States

Daylight saving time ends at 2 a.m. local time on Sunday, which means you need to set your clock back an hour before you go to bed. Standard Time will last until March 9, when we will “step forward again” with the return of Daylight Saving Time.

This spring time change can be harder on your body. Darker mornings and lighter evenings can disrupt your internal body clock, making it harder to fall asleep on time for weeks or longer. Studies even found a slight increase in heart attacks and strokes right after the March time change.

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

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 better aligns with the sun — and biology human.

Most countries do not observe daylight saving time. For those who do – mainly in Europe and North America – the date the clocks are changed varies.

Two states – Arizona and Hawaii – are not changing and staying on standard time.

Here’s what you need to know about the biannual ritual.

How the body reacts to light
The brain has a master clock that is set based on exposure to sunlight and darkness. This circadian rhythm is an approximately 24-hour cycle that determines when we become sleepy and when we are more alert. Patterns change with age, one reason why young people who grow up early become difficult-to-wake teenagers.

Morning light resets the rhythm. In the evening, levels of a hormone called melatonin begin to increase, triggering sleepiness. Too much light in the evening – that extra hour compared to daylight saving time – delays this surge and the cycle becomes out of sync.

And this circadian clock affects more than just sleep, also influencing things like heart rate, blood pressure, stress hormones, and metabolism.

How do time changes affect sleep?
Even a time change can disrupt sleep schedules, because even though the clocks change, work and school start times remain the same.

This is a problem because many people are already sleep deprived. About one in three American adults sleep less than the recommended seven hours per night, and more than half of American adolescents do not get the recommended eight hours on weeknights.

Lack of sleep is linked to heart disease, cognitive decline, obesity and many other problems.

How to prepare for the time change
Some people try to prepare for a time change by gradually changing their bedtimes in the days leading up to the change. There are ways to make the adaptation easier, including getting more sunlight to help you reset your circadian rhythm and enjoy healthy sleep.

Will the United States ever get rid of the time change?
Lawmakers sometimes propose doing away with the time change altogether. The most significant recent attempt, a now-stalled bipartisan bill called the Sunshine Protection Act, proposes to make daylight saving time permanent. Health experts say lawmakers have taken things the other way: Standard time should become permanent.

Aubrey Jarrell, a dairy farmer from Kentwood, Louisiana, isn’t a fan of the time change. He said it interfered with his cows’ strict milking routine and caused them stress “and stress for a dairy cow is not good.” There is a drop in milk production until they adapt, he said.

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

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