If you live in a northern climate, you know that the cold, gray days of winter can really wreak havoc on your mood.

Around 6 to 9 percent of the US population suffers from full-blown Seasonal Affective Disorder (SAD) during winter when the days are short and the weather is cold; symptoms include weight gain, sleepiness, low energy and irritability. About 75 percent of SAD sufferers are female.

Another 14 percent of the population experiences the winter blues, a milder version of SAD that can leave you feeling unmotivated, unsociable and craving high carbohydrate foods.

SAD isn’t all in your mind. It’s a biological reaction to the lack of sunlight that comes with short days and gray skies.

The reduced exposure to light in winter decreases your brain’s production of serotonin, a chemical that regulates your mood and disrupts the production of melatonin (a hormone that regulates your sleep patterns).  SAD can be debilitating all on its own, but it can be devastating when it complicates existing problems such as addiction or bipolar disorder.

Antidepressants can be helpful in treating severe cases of SAD but there are plenty of non-pharmaceutical treatments, too – light therapy is one of the most common. As much as 70 percent of SAD sufferers see improvement by simply sitting in front of a bright light or a light therapy box for 15-90 minutes a day, usually in the morning.

Getting outside in the natural sunlight and exercising can be helpful, too.  For those that suffer from winter blues rather than full-blown SAD, it might be enough to change your attitude about winter, rather it be cold-weather activities, like sledding and ice-skating, or cozy cold weather rituals, like sitting by the fire with hot chocolate or slowing down to enjoy a good book.