Quality of life as an outcome indicator in patients with seasonal affective disorder: Results from the Can-SAD study

Background. Although a host of studies have now examined the relationship between quality of life (QoL) and non-seasonal depression, few have measured QoL in seasonal affective disorder (SAD). We report here on results from the Can-SAD trial, which assessed the impact of treatment with either antidepressant medication or light therapy upon QoL in patients diagnosed with SAD. Method. This Canadian double-blind, multicentre, randomized controlled trial included 96 patients who met strict diagnostic criteria for SAD. Eligible patients were randomized to 8 weeks of treatment with either: (1) 10000 lux light treatment and a placebo capsule or (2) 100 lux light treatment (placebo light) and 20 mg fluoxetine. QoL was measured with the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q) and the Medical Outcomes Study (MOS) Short-Form General Health Survey (SF-20) at baseline and 8 weeks. Results. Both intervention groups showed significant improvement in QoL over time with no significant differences being detected by treatment condition. Q-LES-Q scores increased significantly in seven of eight domains, with the average scores rising from 48.0 (S.D. = 10.7) at baseline to 69.1 (S.D. = 15.6) at week 8. Treatment-related improvement in QoL was strongly associated with improvement in depression symptoms. Discussion. Patients with SAD report markedly impaired QoL during the winter months. Treatment with light therapy or antidepressant medication is associated with equivalent marked improvement in perceived QoL. Studies of treatment interventions for SAD should routinely include broader indices of patient outcome, such as the assessment of psychosocial functioning or life quality.