New York, Oct 11 (IANS): Regular exposure to the bright white light at midday can significantly decrease symptoms of depression and increase functioning in people with bipolar disorder, reveals a new study.

Bipolar disorder, also known as manic-depressive illness, is a brain disorder that causes unusual shifts in mood, energy and activity levels. 

The findings showed that people exposed to bright white light between noon and 2:30 p.m. for six weeks experienced a significantly minimal depression rate and returned to normal functioning. 

Over 68 per cent of patients who received midday bright light achieved a normal level of mood, compared to 22.2 per cent of patients who received placebo light.

Further, bright light therapy also reduced the average depression score to 9.2 compared to 14.9 to those to the placebo group, the researchers said.

"Effective treatments for bipolar depression are very limited," said lead author Dorothy Sit, Associate Professor at Northwestern University, Illinois in the US. 

The new light therapy "gives us a new treatment option for bipolar patients that we know gets us a robust response within four to six weeks", Sit added.

The light therapy, which also had minimal side effects, has conventionally been tested using morning light at awakening because previous research has suggested that morning light helps reset circadian rhythms and can be helpful in the treatment of SAD, Sit said. 

However, the mechanism of response is unclear in bipolar disorder, he noted. 

For the study, published in the journal American Journal of Psychiatry, the team divided participants with moderate depression, bipolar disorder, into two groups receiving bright white light and placebo light. 

The participants were instructed to increase their exposure to the light therapy by 15-minute increments until they reached a dose of 60 minutes per day for four weeks or experienced a significant change in their mood.