Fall Back

Daylight Saving Time: 4 negative effects on the mind and body to watch for

Here's what to expect when clocks fall back.


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This Sunday, the U.S. is scheduled to set the clocks back – leaving us with an additional hour of daylight in the early morning, and one hour fewer in the afternoon. It marks the end of daylight saving time, (DST) which began in March.

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The experience might leave you feeling a bit groggy.

It's not all in your head.

Shifting our schedules ahead by one hour, as we do in the spring, can mess with our circadian rhythm, a cycle of hormone release and other bodily processes tied to cycles of light and dark.

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There's more light in the afternoon, and less in the morning, creating a mismatch between our internal clocks that follow that light and the social clocks that run our lives.

But switching back, as we're about to do, can also be disruptive.

It can affect our sleep and mood in the weeks after the change happens. >>

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You may not end up sleeping more when the clocks fall back.

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When we set the clocks back in the fall, we get to do an entire hour of sleep all over again, in theory.

A 2013 review paper notes that there is "little evidence" that people actually get more sleep that night.

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The review points to a 2010 study analyzing the sleep patterns of 88 people five days before and five days after the clocks shifted back one hour.


The team found no significant changes in sleep duration during the night of the transition. People did get up about 20 minutes earlier, on average, the first four days after the transition.

The return to standard time could still affect sleep for days.

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A 2012 study of 120 people found that short sleepers, people who slept less than 7.5 hours, actually got about 20 more minutes of sleep in the days following the autumn time change. But that sleep tended to be heavily disrupted.

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People who regularly slept for more than 8.5 hours ended up sleeping less than usual days after setting the clocks back.

7 minutes

All sets of sleepers took about 7 minutes longer to fall asleep after the shift.

They also had lower sleep efficiency, which means they spend more of their time in bed awake.

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Falling back doesn't just affect sleep.

It can also affect mood.

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A 2016 study found that the number of people diagnosed with seasonal depression in Denmark increased 11 percent right after the clocks are set back, and dissipated in the weeks following.


The study was based on 185,419 depression diagnoses collected between 1995 and 2012.

The study's author, Søren D. Østergaard at Aarhus University Hospital said he was "relatively sure" it was the transition into standard time that caused the uptick.

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"The transition to standard time is likely to be associated with a negative psychological effect as it very clearly marks the coming of a period of long, dark, and cold days."

Finally, you may have never completely adjusted to DST in the first place.

In a 2008 study on 50 people, scientists found that our circadian rhythms tend to align with dawn under standard time (the time we will enter this Sunday).

But when DST was enacted in the spring, some people's internal clocks never fully adjusted.

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Morning larks, or people who tend to rise early and go to bed early, were able to advance their "center of activity" or the part of the day when they were the most active by 40 minutes when the clocks were pushed forward by one hour.

Night owls, people who naturally stay up late and rise long after sunrise, weren't able to advance their center of activity at all during the eight-week study.


It's also important to note that other experts suggest that it is possible to adjust to the time change.

5 to 7 days

It varies person to person. But the American Academy of Sleep Medicine suggests it takes about five to seven days to adjust to a time change.

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It's the transitions that can be hard to navigate.

This is why some scientists argue that it's time to do away with time changes for good.

Read more about daylight savings time and the body clock here.

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