The causes of PMS and PMDD have not been identified, although social, cultural, biological, and psychological factors all appear to be involved. Researchers estimate that PMDD affects between 3% and 8% of women in their reproductive years. Major depression is very common with PMDD, although PMDD can occur in women who do NOT have a history of major depression. Studies have found that women who have seasonal affective disorder (SAD), a form of depression characterized by annual episodes of depression during fall or winter that improve in the spring or summer, are likely to also have PMDD.
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