by Diane Wrigley, Physician Assistant — Certified
One person in five will experience a depressive episode in his or her life, but only five percent of the population suffers from full-blown SAD. Another ten to twenty percent of the population suffers from at least some of the symptoms of SAD.
A distinct subtype of recurrent depressive illness, SAD differs from other forms of mental illness (such as unipolar and bipolar depression) in that its symptoms only manifest themselves seasonally—generally starting in autumn and continuing through the winter months.
SAD patients manifest many of the same symptoms as those who suffer from other types of depression, including negative feelings about the past, present and future, excessive sleep, increased appetite, mood swings and irritability, and impaired memory and concentration. Depressive episodes often impair the patient's ability to work or function fully in family or social settings. Also, like more generalized depression, women are more likely to suffer from SAD than men. Studies show that women are twice as likely to be treated for depression than men; the reason remains unclear. It could be physiological, or it could be because women are more likely to seek help, or because men simply tend to deny their symptoms.
Unlike other types of depression, however, many studies of SAD show that those who suffer are consistently depressed only during those seasons with diminished daylight. In particular, studies done at research stations in Antarctica showed that even individuals who do not strictly fit SAD's clinical criteria showed an increased incidence (10 to 28%) of depressive symptoms during the winter.