By Leslie Thompson The leaves are falling and the brisk, cool air of fall is permeating the streets. Winter is just around the corner, but instead of embracing the seasonal change, you’re feeling a bit down, a little moodier, or even depressed. If this sounds like you, know that you’re not alone: Many people suffer from these same symptoms once the temperature drops. Although many brush it off as simply a case of the winter blues, seasonal affective disorder (also known as SAD) is a type of depression that occurs annually—most often during the fall and winter months. Seasonal affective disorder is cyclic type of depression that occurs during the same season each year: winter onset and summer onset. It is estimated that as many as half a million Americans suffer from winter-onset SAD, and another 10-20 percent experience a mild case of depression during the fall and winter seasons. More women than men are affected; although this disorder doesn’t usually start until adulthood, the risk of developing SAD decreases as one ages. Common symptoms of winter-onset seasonal affective disorder include feelings of depression and/or hopelessness, loss of energy, increased anxiety and irritability, difficult concentrating, and changes in appetite. People suffering from SAD may also avoid social situations and lose interest in activities they once enjoyed. Summer-onset seasonal affective disorder shares many of the same symptoms as winter onset, but also includes insomnia and increased sexual drive. Both types of SAD may also include symptoms found in other types of depression including feelings of guilt, extended feelings of hopelessness, and physical ailments such as headaches. No one knows for sure what causes seasonal affective disorder. However, researchers believe there are a few specific factors that may contribute to the disorder. First, the reduced hours of sunlight may disrupt an individual’s internal clock, leading to feelings of depression. Melatonin—the hormone that affects sleep—reaches its highest level during the fall and winter months when the nights are longer. The change in season can also cause low levels of serotonin—a brain chemical that affects mood—in the body, which can also lead to feelings of depression. There are several treatment options for individuals suffering from seasonal affective disorder. For most people diagnosed with SAD, light therapy is the most effective—it is estimated that 75-85 percent of SAD sufferers benefit from this type of treatment. Other forms of treatment include medication, psychotherapy, stress management, and environmental changes. The most important thing is to seek professional help if you think you or a loved one may have seasonal affective disorder so you can enjoy the change in seasons.