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What is seasonal affective disorder, and why do people get it?

What is it about winter time that makes people so gloomy and introverted?

In part, it’s caused by the season’s darkness — not the cold, according to a Vox article explaining the condition known as Seasonal Affective Disorder.

It’s dark when you get up in the morning, and dark when you go home from work. Darkness comes at a different time, but we are on the same schedule year-round. Your body’s circadian rhythm is off.

Your body makes the hormone melotonin at night because it makes us drowsy. Light exposure suppresses its production. So when you don’t see the sun in the morning, you may not stop producing it — and since it gets dark so many hours before you go to sleep, you may start producing it too early. As Vox points out, “researchers have found people who have melatonin production that begins too many or too few hours before they go to sleep at night have the highest rates of SAD.”

According to a study on SAD published in the journal Psychiatry, it effects between 1.7 and 9.7 percent of people in the U.S., with the highest percentages coming in the northern states. It’s still not clear why it causes depression and other symptoms beyond just tiredness.

Treating SAD is relatively simple — it involves sitting near a special type of light each day — though a doctor would need to diagnose you before you can begin treatment.