A new study is shedding light on the relationship between depression and bipolar disorder.
Researchers at the National Institute of Mental Health in Bethesda, Maryland analyzed a survey of more than 5,000 U.S. households. They found that nearly 40% of Americans with major depression also display a mild type of manic behavior called "subthreshold hypomania."
The study showed higher rates of anxiety and substance abuse among depressed patients with subthreshold hypomania. They also had more depressive periods than depressed people without any manic behavior.
What's more, researchers noted a family history of mania among patients with subthreshold hypomania, which could put them at higher risk of developing full-blown bipolar disorder later in life.
People with subthreshold hypomania have brief but recurring periods where they are noticeably more active, energetic and more easily agitated than usual. Unlike with bipolar disorder, the mild manic periods typically last fewer than four days and don't impair their lives.
The study is published in the "American Journal of Psychiatry."