SATURDAY, Dec. 20 (HealthDayNews) -- While most people simply grumble about the cold weather and shortened days of winter, the season can mean a case of the blues for one in four Americans.

Worse yet, 5 percent of the U.S. population suffers from a serious depression during the winter known as seasonal affective disorder (SAD).

Some symptoms of SAD are changes in sleeping and eating habits, a persistent blue or anxious mood, and a loss of pleasure from activities, according to the National Mental Health Association.

Other symptoms might include cravings for sweet or starchy foods, weight gain, fatigue, irritability and difficulty concentrating, reports the American Academy of Family Physicians. These symptoms will generally occur in the fall and winter months and subside during the spring and summer. Symptoms are usually at their worst during January and February, when the days are shortest.

Young adults and women are at the highest risk for developing the disorder, and it is more common in northern areas of the world.

While researchers have yet to pinpoint the exact cause of SAD, they believe that increasing levels of the sleep-related hormone melatonin may be at the root of the disorder. The more time a person spends in the dark, the higher the melatonin levels.

That may be why light therapy is one of the most effective treatments for people with SAD. Natural light is best, and if you can spend an hour outdoors on winter days, you will probably see an improvement in your mood, according to the mental health association. For those suffering severe symptoms, phototherapy -- sitting in front of a light box that emits very bright light -- may be helpful.

More information

Here's more seasonal affective disorder.