Psychic and somatic anxiety differentially predict response to light therapy in women with seasonal affective disorder

Abstract

Objective To examine whether psychic and/or somatic anxiety predict responsiveness to light therapy in women with winter Seasonal Affective Disorder (SAD). Design Eighty-one women with SAD were administered a standard 10-day trial of light therapy administered for one-half hour in the early morning. Using a multiple regression model, baseline somatic and psychic anxiety item scores were used to predict percentage change scores on the 29-item SIGH-SAD post treatment. Baseline scores for weight gain, hypersomnia and the total SIGH-SAD were also included as predictor variables. Results The regression model was highly significant ( F = 4.63, df = 5, 75; p = .001; model R 2 = .236), with both psychic anxiety and somatic anxiety contributing significantly to the model. Consistent with prior work using anti-depressant medication in non-seasonal depression, psychic anxiety was positively correlated with outcome, while somatic anxiety negatively predicted outcome. Conclusions In SAD, psychic and somatic anxiety scores at baseline appear to be independent and opposite predictors of light therapy response. These effects were independent of baseline scores for weight gain and hypersomnia, two previously established predictors of response to light. These findings may be an important consideration in the design and interpretation of light therapy studies of SAD.