Has your mood fallen as fast as the thermometer? If so, you may be suffering from the winter blues, and you’re not alone. An estimated 10 million Americans suffer from seasonal affective disorder, or SAD. It’s a type of depression occurring in the winter months, and its severity depends partly on geography. Only 1 percent of people residing in sunny Florida suffer from SAD versus 10 percent of people in blustery New Hampshire.

Why’s that? Lack of sunlight during winter days causes the brain to produce excess melatonin (the hormone that helps you sleep) and less serotonin (the hormone that perks you up). SAD results from this hormonal imbalance. Common symptoms of SAD include feeling melancholy and fatigued, disinterest in socializing, weight gain and a sudden change in appetite.

What can you do to combat the winter blues? Small lifestyle changes can help if you find yourself with a case of the mid-winter doldrums.

First, get outside. For many people, winter’s shorter daylight means it’s dark when they go to work and return home, leaving no time to get outside and soak in the light. Make the most of the short days by taking a walk outside during lunch or exercising outside on the weekends.

Second, eat smart. Foods high in sugar and fat feel euphoric for a moment but result in an ugly energy crash. Keep your body well-fed with proteins, vegetables and greens high in nutrients.

Third, help others. Studies show that volunteering dramatically improves mental health, so spending time giving back to the community can lift your spirits.

If these tricks don’t work, you can always head to a sunny beach. A few January days in a warm climate can zap the winter blues away.