Researchers say study participants who were exposed to bright white light therapy experienced a reduction in depression symptoms.

Light therapy has been shown to be an effective treatment for seasonal affective disorder.

Now, a study concluded that light therapy administered at midday shows strong promise for treatment of bipolar depression as well.

“Effective treatments for bipolar depression are very limited,” said Dr. Dorothy K. Sit, an associate professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine and the study’s lead author, in a press statement. “This gives us a new treatment option for bipolar patients that we know gets us a robust response within four to six weeks.”

Researchers at Northwestern University conducted a small six-week randomized, double-blind, placebo-controlled study on the effect of adjunctive bright light therapy on bipolar depression.

This form of depression is part of bipolar disorder, a chronic illness characterized by severe mood swings.

The study involved 46 patients who were taking antimanic medications.

Half were assigned to receive 7,000-lux bright white light therapy while the other half received 50-lux dim red light sessions as a placebo.

Treatment was delivered via a “light therapy box,” a device that gives off bright light similar to daylight.

All participants began the study with moderate depression, but researchers found that those who received the bright light therapy experienced significantly higher remission rates — in other words, reduced depression to the level of “normal mood” — than those receiving the placebo. 68 percent compared to 22 percent.

Average depression scores also were much lower among the light therapy group (9.2 on the Hamilton Depression Scale, indicating mild depression) than the placebo group (14.9, a score falling in the range of moderate depression) at the end of the study.

Both the treatment and placebo groups experienced improved sleep quality.

Improvements were observed within four weeks of treatment initiation — similar to the findings of past studies on using light therapy for non-seasonal depression and depression during pregnancy.

The net effect was that the light therapy patients were able to return to work or complete household chores that their depression was preventing prior to treatment.

“The data from this study provide robust evidence that supports the efficacy of midday bright light therapy for bipolar depression,” study researchers wrote.

“The findings are clear but not that surprising,” Dr. Michael Thase, a professor of psychiatry and an expert on bipolar disorder at the University of Pennsylvania’s Perelman School of Medicine, told Healthline. “There’s a lot of research showing that light therapy has an antidepressant effect.”

Thase added that the research is an “interesting preliminary finding,” stressing that a larger study will be required to adequately assess risks associated with the therapy that may have been missed in the small group of subjects in the Northwestern study.

The reductions in depression attributed to light therapy were actually better in the Northwestern study than those in large-scale studies of “second generation” antipsychotics used to treat bipolar disorder, such as Latuda, said Thase.

However, he pointed out that large studies often fail to realize the full promise of smaller ones.

“This tells us we need to invest in a follow-up study,” he said.

Some past research has suggested that unsupervised use of light therapy could cause increased mania among people with bipolar illness.

However, no mood polarity switches were observed in this study’s participants, researchers said.

Study participants were initially instructed to place the light box about a foot from their face for 15-minute sessions.

Exposure was increased in 15-minute increments until subjects either reached a dose of 60 minutes daily or experienced a significant change in their mood.

“By starting at a lower dose and slowly marching that dose up over time, we were able to adjust for tolerability and make the treatment suitable for most patients,” said Sit.

Sit has conducted some of the seminal research on using light therapy to treat bipolar disorder, including a 2007 study showing that a majority of women with bipolar depression benefited from exposure to bright light. That study also found that therapy worked best when given for a short duration initially.

Thase pointed out that light therapy also doesn’t cause some of the unpleasant side effects associated with antipsychotic drugs, including dry mouth, weight gain, and sexual dysfunction.

A Peking University study published in September in the Journal of Affective Disorders also found that bright light therapy (BLT) had a greater ameliorative effect on bipolar depression than a placebo, with no increase in hypomania symptoms.

“BLT can be considered as an effective and safe adjunctive treatment for patients with acute bipolar depression,” that study concluded.

Bright light therapy has also been used as an alternative treatment for alcohol use disorder as well.