Leo Sher, M.D.

Our research work “Early response to light therapy partially predicts long-term antidepressant effects in patients with seasonal affective disorder” was published 25 years ago in the 2001 issue of the Journal of Psychiatry and Neuroscience (1).

Our study examined whether patients with seasonal affective disorder (SAD) who improve very quickly after starting light therapy are more likely to experience sustained antidepressant benefits over time. We studied 12 patients with SAD who were treated with bright light therapy for two weeks at the National Institutes of Health Clinical Center. Depression severity was measured using the Structured Interview Guide for the Hamilton Depression Rating Scale–Seasonal Affective Disorder Version (SIGH-SAD) before treatment, after one hour of light exposure, and again after one and two weeks of therapy.

We found that some patients showed measurable improvement in atypical depressive symptoms after only one hour of light therapy. Importantly, this very early improvement correlated with better outcomes after two weeks of treatment. The findings suggest that an immediate response to light exposure may serve as a partial predictor of longer-term antidepressant benefit in SAD. However, the correlation was stronger for atypical symptoms—such as hypersomnia, fatigue, and increased appetite—than for typical depressive symptoms.

Because the sample size was small, we emphasized that the results should be interpreted cautiously and require replication in larger studies. Nevertheless, the study supported the idea that light therapy can produce rapid biological and mood effects in susceptible individuals. The paper also contributed to growing evidence that SAD has a strong relationship to circadian rhythms and environmental light exposure. Clinically, the study suggested that early response patterns could potentially help physicians identify which patients are most likely to benefit from continued light therapy. Overall, our article reinforced light therapy as an effective treatment for SAD while highlighting the possibility of using rapid symptom improvement as an early prognostic marker.

Reference

1. Sher L, Matthews JR, Turner EH, Postolache TT, Katz KS, Rosenthal NE. Early response to light therapy partially predicts long-term antidepressant effects in patients with seasonal affective disorder. J Psychiatry Neurosci. 2001 Sep;26(4):336-8.