Blue light therapy for seasonal and nonseasonal depression Original paper

Light therapy (daily exposure to bright light) appears to benefit seasonal and nonseasonal depression. Although light is the strongest synchronizer of circadian rhythm (part of the purported underlying mechanism behind light therapy’s benefits, mediated in part by suppression of melatonin secretion and modulation of serotonin), the key photopigment in the eye that modulates the circadian effect of light (melanopsin) is particularly sensitive to shortwave blue light.

This meta-analysis included 9 randomized controlled trials involving a total of 347 participants with seasonal major depressive disorder (MDD; 7 studies) or nonseasonal MDD (2 studies). Four studies compared blue light to an inactive light condition (red or orange light), and 5 studies compared it to an active condition (white fluorescent light). Study treatment duration and daily light exposure ranged from 5 to 42 days and from 20 to 240 minutes, respectively.

The participants’ depressive symptoms were evaluated by clinicians using the Structured Interview Guide for the Hamilton Depression Rating Scale for Seasonal Affective Disorder (6 studies), Atypical Depression Supplement (2 studies), or Hamilton Depression Rating Scale-17 (1 study).

Blue light treatment did not change depressive symptoms when compared to either active or inactive light conditions.

The authors noted that in sensitivity analyses, blue light performed similarly to the active conditions, suggesting that low-intensity blue light could be as effective as standard light therapy, but more research will be needed for confirmation.