Aug. 17, 2010 — Researchers have discovered clues that may help identify which people with depression are at risk of developing bipolar disorder. The new findings appear in the online version of The American Journal of Psychiatry.

Bipolar disorder is a serious condition characterized by the extreme highs of mania and devastating lows of depression. Nearly 40% of people with a history of major depression also report recurrent episodes of low level, subtle hypomania, the new study showed.

Less intense than mania, hypomania is marked by bursts of increased energy, activity, and less need for sleep. The episodes reported by nearly 40% of the study participants were not full-blown mania or even full-blown hypomania, but more mild and dubbed “sub-threshold hypomania.”

“People with a history of depression who have recurrent episodes of a day or two of increased energy, activity, and decreased sleep and then go back to their usual level of function may be more likely to develop bipolar disorder in the future,” says study author Kathleen Merikangas, PhD, a senior investigator and chief of the genetic epidemiology branch in the Intramural Research Program at the National Institute of Mental Health in Bethesda, Md.

“The earlier bipolar disorder is recognized and treated, the less consequences there are of manic episodes such as substance abuse and trouble with the law,” she says. “These people should be monitored carefully, not just put on antidepressants.”

The study included information from members of more than 5,000 households across the U.S. who participated in face-to-face interviews between February 2001 and April 2003. The interviews focused on having a history of mood disorders, their symptoms, and the severity of their symptoms.

Family History of Mania Raises Risk

Another major risk factor highlighted in this study is a family history of mania. In fact, family history of mania was as common in people with sub-threshold hypomania as it was in people with full-blown mania, the study showed.

Study participants with depression and subthreshold hypomania also developed mood disorders at a younger age and had more anxiety, substance abuse problems, and depressive episodes than their counterparts who experienced depression on its own.

“If you notice these up-and-down shifts even if they are only short lived in yourself or in a loved one with depression, seek evaluation by a mental health professional,” she says. Mental health experts are more apt to recognize whether these behaviors are the seeds of bipolar disorder or people are just truly starting to feel better, Merikangas says.

Study Strengthens Link

Gregory Simon, MD, a psychiatrist and researcher at the Group Health Research Institute in Seattle and chair of the scientific advisory board of the Depression and Bipolar Support Alliance, a Chicago-based nonprofit group that focuses on promoting awareness and education about the two conditions, says previous research has shown that there is not a sharp dividing line between depression and bipolar disorder.

“Instead, there is a continuous shading from pure depression to classic bipolar disorder,” Simon tells WebMD. “This study gives stronger evidence for that continuous shading and demonstrates more clearly that milder symptoms of hypomania are truly related to bipolar disorder.”

Warning signs that a person with depression is at risk for bipolar disorder may include periods of increased energy, decreased need for sleep, rapid thoughts, or irritability, he says.

“When these problems are milder or briefer, though, they are harder to distinguish from anxiety or other more common problems,” he says. “People who have mild or brief periods that suggest hypomania should watch more closely for signs of definite bipolar disorder.”