The days are getting shorter, the nights are getting colder, and before you know it, a familiar face will be on your doorstep. No, I’m not talking about Santa Claus. It’s Seasonal Affective Disorder, or SAD, and it can cause depression, difficulty concentrating, excessive eating, and (surprise, surprise) weight gain.

SAD was first noted before 1845, but was not defined until 1984 by Dr. Norman Rosenthal at the National Institute of Mental Health. Since then, researchers have discovered interesting trends, including

• SAD occurs four times more often in women than in men.
• Symptoms of SAD usually appear during a person’s twenties.
• SAD rarely affects those living within thirty degrees of the equator, where daylight is long and very bright.
• Those who work or study in windowless rooms are at an increased risk for developing SAD.

Melatonin, a sleep-related hormone, is widely regarded as a major contributing factor to SAD. This hormone, which can cause symptoms of depression, is at its peak production when days are short and dark. And it follows that those who live in northern climates suffer from longer and more profound bouts of SAD.

Today, SAD affects more than 10 million Americans. But don’t let the winter blues stop you in your snow tracks! There are some simple steps that you can take to stay happy and healthy, even during winter’s darkest days.