Body Mass Index and Atypical Balance as Predictors of Seasonal Affective Disorder Treatment Outcomes

Background: Light therapy (LT) and cognitive behavioral therapy (CBT-SAD) are efficacious treatments for winter seasonal affective disorder. Patient baseline characteristics may differentially predict treatment outcomes. Dimitrova and colleagues (2017) found higher baseline body mass index (BMI) and higher atypical balance were positive prognostic indicators of depression outcomes after six weeks of LT for SAD. The present study investigates BMI and atypical balance as predictors of acute and long-term SAD treatment outcomes. Methods: In a randomized clinical trial,177 adults diagnosed with Major Depression, Recurrent with Seasonal Pattern received either CBT-SAD (n = 88) or LT (n = 89). BMI was determined at baseline. Atypical balance was derived using the Structured Interview Guide for the Hamilton Rating Scale for Depression–Seasonal Affective Disorder Version (SIGH-SAD). Depression status was assessed at post-treatment and first and second winter follow-ups via the SIGH-SAD and the Beck Depression Inventory-Second Edition (BDI-II). Hierarchical regression was used to investigate main effects of treatment type, BMI, atypical balance and their interactive effects on treatment outcomes (i.e., depression scores, remission status, and SIGH-SAD recurrence status). Results: Analyses revealed a significant BMI × treatment interaction in predicting SIGH-SAD remission status at second winter follow-up. A probe of the interaction revealed that the probability of SIGH-SAD remission at Winter 2 was higher in LT at lower BMI, but higher in CBT-SAD at higher BMI. Analyses also revealed a significant atypical balance × treatment interaction in predicting SIGH-SAD remission at first and second winter follow-up. The same pattern emerged in probing each interaction effect: the probability of SIGH-SAD depression remission was higher in LT than CBT-SAD at lower atypical balance, but higher in CBT-SAD than LT at higher atypical balance. Conclusions: BMI and atypical balance are useful prescriptive factors for predicting long-term SAD treatment outcomes. For patients with higher baseline BMI or atypical balance, CBT-SAD is associated with a greater likelihood of remission in future winters than LT. For patients with lower baseline BMI or atypical balance, LT is associated with a higher likelihood of remission in future winters than CBT-SAD. This work can potentially inform precision medicine efforts for SAD