As the days grow shorter and daylight is scare, some Americans find they are oversleeping, overeating, gaining weight and withdrawing from social activities. These symptoms may be part of a condition called seasonal affective disorder, also known as SAD, or seasonal depression. According to the National Institutes of Health, seasonal depression is defined as periods where people feel sad or unlike themselves, typically when seasons change, says USA Today.

The condition affects an estimated 10 million Americans, with women four times more likely to be diagnosed than men. It’s a type of depression linked to changing of the seasons, especially when the days get shorter, and the weather is colder.

But many people, while not developing clinical symptoms of SAD, may experience the winter blues and suffer from fatigue, sadness, difficulty concentrating and disruptive sleep during the colder seasons. These symptoms may be temporary but could decline into depression if not treated. The main difference between the winter blues and SAD is severity and function, says Georgia Gaveras, chief psychiatrist, and co-founder of Talkiatry.

“People feel sad sometimes, and there is nothing wrong with that. In fact, having emotions is part of what makes us all human and something we don’t want to extinguish,” she tells Verywell Mind. Gaveras adds that most people with SAD have signs of a major depressive disorder that can interfere with daily functioning.

Dr. Norman Rosenthal, author of the groundbreaking book, Winter Blues, who first described SAD and pioneered the use of light therapy in its treatment, tells Newsmax that several factors contribute to feeling blue in the winter.

“These include a genetic component, stress, and a lack of environmental light,” he explains. “We can feel sad at any time of the year and it’s part of the normal palette of human emotions. For example, we feel sad when we fail to reach a goal, have a setback, or lose someone we love. But SAD is a specific condition that affects people predominantly during the winter months.”

Here are some tips to stay mentally healthy this winter:

• Get more light. Rosenthal, a renowned psychiatrist, says you should go outdoors as often as you can. “Even on a winter day you can get a lot of light coming from the sky,” he says. If you can’t get out, he suggests bringing more light fixtures indoors. “You can buy those specially built for treating SAD. The lightbox should be big enough — at least one foot square, made by a reputable manufacturer, and ideally used in the morning or any time of day.” The light boxes give off 10,000 lux, says USA Today, which is a unit of illuminance. Make sure the boxes are equipped with UV filters to protect your skin and follow the directions carefully. Tanning beds are not effective, say experts.

• Exercise regularly. Physical activity has been shown to boost mood, decrease the symptoms of depression and reduce stress, according to the American Psychological Association. Start slowly and build up to 30 to 60 minutes a day, five days a week. Find an activity you like to do so that you will be more likely to stick with it.

•Try to minimize stress. Rosenthal says we should try to identify our stressors, and if they are unavoidable, figure out ways to deal with them. Very often, being indoors means more screen time so try to limit your exposure to negative news and limit the amount of time you spend staring at a screen.

• Boost your mood with food. Heidi Hanna, a leading expert on the mind-body connection, tells Newsmax that choosing foods carefully can curb sugar and carbohydrate cravings throughout the day and help stabilize your mood. “Include a balance of natural sources of complex carbohydrates, lean protein and healthy fat that keep blood sugar levels stable throughout the day. You should also consume a rainbow of produce to provide antioxidants,” she says. Foods rich in vitamin D such as fatty fish, fish oil, vitamin D fortified foods like milk, orange juice, breakfast cereal and yogurt can help the winter blues.