Optimized light therapy for non-seasonal major depressive disorder: effects of timing and season

Light Therapy (LT) when combined with standard antidepressant treatment for unipolar depression hastens recovery. We studied the influence of LT timing on the antidepressant efficacy of LT and the influence of the season of treatment and recurrence on the response to treatment.

We studied 70 inpatients affected by Unipolar Depression, treated for three weeks with combined LT and venlafaxine. Two-third of the patients received LT following a predictive algorithm based on MEQ scores; the others received LT at 11:00 a.m. Severity of depression was rated on the Hamilton Depression Rating Scale (HDRS). A subgroup of patients wore activity monitors.

HDRS scores significantly decreased during treatment (Friedman's ANOVA: χ2=186.82, p<0.00001). LT administered in the early morning showed a better relative efficacy than late morning (F=4.576; p=0.012) with the clinical improvement correlating with an advance in rest-activity rhythm acrophase (r=-0.336; p=0.017). Season of hospitalization interacted with LT timing and time in influencing response to treatment (F=3.101; p=0.049) and season of episode recurrence significantly interacted with LT timing, season of hospitalization and time (F=5.925; p=0.0035).

The major limitation of the study is the small sample size when considering simultaneously LT schedules, season of treatment and recurrence. Moreover, even if none of the patients fulfilled DSM-IV criteria for seasonal pattern of recurrence, they were not administered any questionnaire about seasonality.

We confirmed the usefulness of LT as a non-pharmacological antidepressant therapy for non-seasonal depression. Season and timing of administration and timing of the rest-activity cycle affected response to treatment.