four times more common seasonal affective disorder disease sad SAD seasonal affective disorder Seasonal Affective Disorder What Is Seasonal Affective Disorder (SAD)? Seasonal Affective Disorder (SAD) What Is Seasonal Affective Disorder (SAD)? seasonal affective disorder Medicine Net 5 percent of adults in the United States five percent of adults SAD seasonal affective disorder seasonal affective disorder MedicineNet.com MedicineNet.com seasonal affective disorder seasonal affective disorder Seasonal Affective Disorder north or south seasonal affective disorder SAD MedicineNet seasonal affective disorder Lifestyle changes