A major study funded by the US National Institute of Mental Health indicates that bipolar disorder has twice the social impact of major depression in terms of lost worker productivity, with reduced productivity lasting even after mood clinically improves, according to an article in the September issue of the American Journal of Psychiatry.

Each US employee with bipolar disorder averaged 65.5 lost workdays per year compared with 27.2 workdays for major depression. Even though major depression is more than six times as prevalent, bipolar disorder costs the U.S. economy nearly half as much -- a disproportionately high 14.1 billion dollars annually.

Researchers led by Doctors Ronald Kessler and Philip Wang of Harvard University, traced the higher toll mostly to bipolar disorder's more severe depressive episodes rather than to its agitated manic periods.

The current study is the first to distinguish the impact of depressive episodes due to bipolar disorder from those due to major depressive disorder in the workplace. Its analysis was based on one-year data from 3378 employed respondents to the National Co-morbidity Survey Replication, a nationally representative household survey of 9,282 U.S. adults conducted in 2001 through 2003.

The researchers measured the persistence of the disorders by asking respondents how many days during the past year they experienced an episode of mood disorder. They judged the severity based on symptoms during a worst month. Lost work days due to absence or poor functioning on the job, combined with salary data, yielded an estimate of lost productivity due to the disorders.

Poor functioning while at work accounted for more lost days than absenteeism. Although only about 1 percent of workers have bipolar disorder in a year compared with 6.4 percent with major depression, the researchers projected that bipolar disorder accounts for 96.2 million lost workdays and $14.1 billion in lost salary-equivalent productivity, compared with 225 million workdays and $36.6 billion for major depression annually in the United States.

About three fourths of bipolar respondents had experienced depressive episodes over the past year, with about 63 percent also having agitated manic or hypomanic episodes. The bipolar-associated depressive episodes were much more persistent -- affecting 134-164 days -- compared with only 98 days for major depression.

The bipolar-associated depressive episodes were also more severe. All measures of lost work performance were consistently higher among workers with bipolar disorder who had major depressive episodes than those who reported only manic or hypomanic episodes. The latter workers' lost performance was on a par with workers who had major depressive disorder.

"Major depressive episodes due to bipolar disorder are sometimes incorrectly treated as major depressive disorder," noted Wang. "Since antidepressants can trigger the onset of mania, workplace programs should first rule out the possibility that a depressive episode may be due to bipolar disorder."