Bright light therapy for bipolar depression: A review of 6 studies

Depressive episodes are part of DSM-5 criteria for bipolar II disorder, and are also often experienced by patients with bipolar I disorder.¹ Depressive episodes predominate the clinical course of bipolar disorder.^2,3 Compared with manic and hypomanic episodes, bipolar depressive episodes have a stronger association with long-term morbidity, suicidal behavior, and impaired functioning.^4,5 Approximately 20% to 60% of patients with bipolar disorder attempt suicide at least once in their lifetime, and 4% to 19% die by suicide. Compared with the general population, the risk of death by suicide is 10 to 30 times higher in patients with bipolar disorder.⁶

Treatment of bipolar depression is less investigated than treatment of unipolar depression or bipolar mania. The mainstays of treatment for bipolar depression include mood stabilizers (eg, lithium, valproic acid, or lamotrigine), second-generation antipsychotics (eg, risperidone, quetiapine, lurasidone, or olanzapine), adjunctive antidepressants (eg, selective serotonin reuptake inhibitors or bupropion), and combinations of the above. While significant progress has been made in the treatment of mania, achieving remission for patients with bipolar depression remains a challenge. Anti-manic medications reduce depressive symptoms in only one-third of patients.⁷ Antidepressant monotherapy can induce hypomania and rapid cycling.⁸ Electroconvulsive therapy has also been used for treatment-resistant bipolar depression, but is usually reserved as a last resort.⁹

Research to investigate novel therapeutics for bipolar depression is a high priority. Patients with bipolar disorder are susceptible to environmental cues that alter circadian rhythms and trigger relapse. Recent studies have suggested that bright light therapy (BLT), an accepted treatment for seasonal depression, also may be useful for treating nonseasonal depression.¹⁰ Patients with bipolar depression frequently have delayed sleep phase and atypical depressive features (hypersomnia, hyperphagia, and lethargy), which predict response to light therapy.¹¹ In this article, we review 6 recent studies that evaluated the efficacy and safety of BLT for treating bipolar depression (Table^12-17).

1. Wang S, Zhang Z, Yao L, et al. Bright light therapy in treatment of patients with bipolar disorder: a systematic review and meta-analysis. PLoS ONE. 2020;15(5):e0232798. doi: 10.1371/journal.pone.0232798

In this meta-analysis, Wang et al¹² examined the role of BLT in treating bipolar depression. They also explored variables of BLT, including duration, timing, color, and color temperature, and how these factors may affect the severity of depressive symptoms.

Study design

• Two researchers conducted a systematic literature search on PubMed, Web of Science, Embase, Cochrane Library, and Cumulative Index of Nursing and Allied Health Literature (CINAHL), as well as 4 Chinese databases from inception to March 2020. Search terms included “phototherapy,” “bright light therapy,” “bipolar disorder,” and “bipolar affective disorder.”
• Inclusion criteria called for randomized controlled trials (RCTs) or cohort studies that used a clearly defined diagnosis of bipolar depression. Five RCTs and 7 cohort studies with a total of 847 participants were included.
• The primary outcomes were depression severity, efficacy of duration/timing of BLT for depressive symptoms, and efficacy of different light color/color temperatures for depressive symptoms.

Outcomes

• As assessed by the Hamilton Depression Rating Scale (HAM-D); Inventory of Depressive Symptomatology, Clinician Rating; or the Structured Interview Guide for the HAM-D, depression severity significantly decreased (P < .05) with BLT intensity ≥5,000 lux when compared with placebo.
• Subgroup analyses suggested that BLT can improve depression severity with or without adjuvant therapy. Duration of <10 hours and >10 hours with morning light vs morning plus evening light therapy all produced a significant decrease in depressive symptoms (P < .05).
• White light therapy also significantly decreased depression severity (P < .05). Color temperatures >4,500K and <4,500K both significantly decreased depression severity (P < .05).

• BLT (at various durations, timings, colors, and color temperatures) can reduce depression severity.
• This analysis only included studies that showed short-term improvements in depressive symptoms, which brings into question the long-term utility of BLT.

2. Lam RW, Teng MY, Jung YE, et al. Light therapy for patients with bipolar depression: systematic review and meta-analysis of randomized controlled trials. Can J Psychiatry. 2020;65(5):290-300.

Lam et al¹³ examined the role of BLT for patients with bipolar depression in a systematic review and meta-analysis.

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