The mood swings. The extended periods of almost superhuman energy. Periods of little or no energy. Feelings of guilt, of worthlessness. Thoughts of suicide, even suicide attempts.

Recognize these symptoms? They're just a few of the classic symptoms of bipolar disorder, a health condition that, according to the National Institute of Mental Health - a division of the National Institutes of Health - affects approximately 5.7 million American adults. That's 2.6 percent of the population.

Or that's what was believed until this week when the Archives of General Psychiatry published a study that reported about 4.4 percent of the U.S. population is affected to some degree with bipolar disorder. That's nearly double the number originally thought to be wrestling with the symptoms of bipolar disorder. The study was funded in part by the National Institutes of Health.

If you know anyone with bipolar disorder, then you know just how serious the condition can be - and how unpredictable a person's actions may be. Bipolar disorder causes extreme mood fluctuations, from periods of deep, dark depression to sudden swings of euphoric 'highs.' Bipolar disorder can also disrupt a person's ability to perform everyday tasks.

While it typically develops late in a person's adolescence or in early adulthood, bipolar disorder has been known to strike individuals in early childhood or even later in their adult years.

Researchers uncovered the new statistics during recent interviews with more than 9,000 individuals chosen from the general population. The researchers based the presence of bipolar disorder as well as its severity of the problem on the number and the magnitude of the manic and depressed episodes.

The research did confirm the previous belief that bipolar disorder usually develops when a person is either in his late teenage years or early adulthood, roughly between the ages of 18 to 22.

Researchers suspect that the increased percentage is not a reflection of more individuals actually being diagnosed with bipolar disorder. Rather, it's more a reflection that a great many people, already diagnosed with depression, may in reality have a form of bipolar disorder.

In fact, most of the people interviewed who displayed symptoms of bipolar disorder were being treated only for depression. This suggests that those individuals being treated for depression may need to be screened for bipolar disorder as well, according to the study.

Bipolar disorder places people at a greater risk of suicide, as well as other medical problems, even such seemingly unrelated health conditions as cardiovascular disease and diabetes.