It is estimated that millions of Americans experience SAD, although many may not know they have this common disorder. In most cases, SAD begins in young adulthood.

SAD occurs much more often in women than in men. Winter-pattern SAD also occurs more often than summer-pattern SAD. Therefore, SAD is more common in people living farther north, where there are shorter daylight hours in the winter. For example, people in Alaska or New England are more likely to develop SAD than people in Texas or Florida.

SAD is more common in people with depression or bipolar disorder, especially bipolar II disorder, which involves repeated depressive episodes and hypomanic episodes (less severe than the typical manic episodes of bipolar I disorder). Additionally, people with SAD tend to have other mental disorders, such as attention-deficit/hyperactivity disorder, eating disorder, anxiety disorder, or panic disorder. Learn more about these disorders.

SAD sometimes runs in families and may be more common in people who have relatives with other mental illnesses, such as depression or schizophrenia.