Seasonal affective disorder (SAD) is an annually recurring depression that typically affects an individual at the same time every year. While some people attribute a run-down feeling to natural winter doldrums, SAD affects thousands of people each year. Here is a basic guide to help you understand this prevalent condition:

Between 4 and 6 percent of Americans experience some form of SAD, according to the American Academy of Family Physicians (AAFP). SAD��can occur��during adolescence or in early adulthood and typically affects more women than men. The disorder is also more common among people who live further from the equator, reports the Mayo Clinic, most likely due to lower levels of sunlight in the winter. This means people from New Hampshire and Alaska are more likely develop SAD than people from Florida.

Symptoms tend to develop slowly as the seasons progress. The symptoms for SAD usually overlap with the symptoms for depression, including changes in appetite, difficulty concentrating, apathy, social withdrawal, mood changes and irritability. Individuals with SAD may appear lethargic, unhappy and disinterested in any activities, including work. Winter or fall-related SAD typically results in weight gain, fatigue and constant sleepiness. People with bipolar (manic depressive) disorder may be affected by SAD in the spring and summer, due to a condition known as reverse seasonal affective disorder, reports the MayoClinic. Symptoms associate with reverse SAD include a persistently elevated mood, hyperactivity, agitation, unbridled or excessive enthusiasm, and rapid thought and speech.

The cause for SAD has yet to be determined, although researchers��attribute the disorder to��a combination of genetics, age and the body’s natural chemical make-up. Your body maintains an internal clock known as your circadian rhythm, and the changing levels of sunlight may disturb that important process. SAD could also occur due to decreased serotonin, which is a brain chemical that helps regulate moods. Reduced sunlight can disrupt both serotonin and melatonin levels. Melatonin affects your mood and sleep patterns, so a disruption can cause sleepiness and depression.

SAD may be treated using the traditional avenues for depression, including therapy and antidepressant medications. Regular exposure to sunlight, exercise and a nutritious diet may help alleviate the symptoms of SAD. The National Institutes of Health recommends making every effort to stay socially active. Light therapy is a popular treatment for SAD. A specialized lamp emits a bright fluorescent light, imitating sunlight and potentially restoring your biological rhythm. You would simply sit in front of the lamp for approximately 30 minutes each day, usually in the morning to mimic sunrise. To take in enough sunlight, keep your eyes open without looking directly at the lamp. Light therapy can come in many different forms, including standard lamps, hats with miniature fixtures and gradually illuminating clocks to replace your alarm. Individuals with bipolar disorder, light-sensitive skin or medical conditions affecting their eyes should be particularly careful when using light therapy.