The science of why daylight saving time is bad for you

This weekend marks the end of daylight saving time. That means that, on Sunday morning at 2 a.m., clocks across America will magically jump back one hour.

For many, this offers a small but valuable treat: An extra hour of sleep. But those extra winks may come at a high cost, according to a new research paper published in the journal Epidemiology. The study shows a drastic spike in diagnoses of depression immediately following the time change. What's going on here?

Roughly 1.6 billion people in about 70 countries observe DST. The exact day and time may differ, but the gist is the same: In the spring, we push our clocks forward, and in the fall we put them back. When we jump back in time, the hour of sunlight that was at the end of the day is now at the beginning. The goal is to make the best use of daylight as the seasons change and the days get either longer or shorter.

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But it seems this transition can have a noticeable effect on many people's psychological health. Why? Because it screws with our circadian rhythm, or internal clock. When this clock gets out of sync, it can alter the chemicals in our brain, leading to depression.

Think about it: That extra hour of daylight you'll get on Sunday morning might not actually do you much good. In the morning, you're likely to be in bed, or in the shower, or commuting to work. Chances are you're not out and about taking in the sunshine. In other words, people may miss out on an hour of daylight that they were able to benefit from when it was in the afternoon, during DST. This is no good when you consider that sunshine itself is also really important for our mental health. Research has indicated that moderate exposure to the sun boosts our vitamin D levels. And for many, the very act of jumping back an hour in time is an unwelcome reminder that dreary weather is coming, and that thought alone may prompt symptoms associated with depression.

Indeed, all of this showed up in the research: According to the study, there is an 11 percent spike in the number of depression diagnoses after the autumn time change. To uncover this statistic, Bertel Hansen of the political science department at the University of Copenhagen, who co-authored the new paper, examined nationwide data between 1995 and 2012 from the Danish Psychiatric Central Research Register, which included 185,419 depression diagnoses.

Perhaps the worst part of his team's findings is this: It takes about 20 weeks after the time change for the number of depression diagnoses to level off. Twenty weeks! That's about five months! "It's not enough to just say, 'Oh they go up,'" says Hansen. "[The diagnoses] have to go up more than what we would expect." And that's exactly what they found.

The team also examined how depression levels changed in the spring, right after jumping forward an hour. They expected to see at least a slight decrease in diagnoses, but found no change at all. That "indicates that it is unlikely to be caused by the one-hour time-shift per se, but rather represents a specific consequence of the turning back of clocks in the fall," the paper says.

So what does all of this mean?

As the end of daylight saving time draws near, it wouldn't be such a bad idea to start shifting your schedule slightly so that you get all of the sunlight your body needs. This could be as simple as waking up a bit earlier or simply taking a walk before work or school. And once Sunday hits, it's worth keeping tabs on your mood and energy level, so you're aware of any significant changes.

Hansen says the point of this new research is not to get rid of DST, but to bring attention to the fact that some people are immediately, negatively impacted by the time change.

His advice for Sunday? "Go outside, do it in the morning, and do it right away."