Benefits of exposure to morning daylight on sleep, circadian rhythms, and symptoms of depression

Background: Current research has shown that depressive symptoms are associated with sleep disturbances and misalignment of circadian rhythms. Thus, a chronobiological intervention associated with the usual antidepressant treatment on depressive symptoms may improve depressive symptoms as long with sleep quality, and circadian rhythms in patients with depression. Methods: The feasibility experimental study was carried out with a total of 38 participants: 21 outpatients suffering from a non-seasonal major depressive disorder (MDD) and 17 healthy volunteers (general population). Twenty-one patients were randomly assigned to two groups: 11 patients received a chronobiological intervention: daylight exposure treatment for 14 days in conjunction with pharmacological treatment (LIGHT group), while 10 patients received only pharmacological treatment (LIGHT group). Depressive severity at the inclusion was assessed with the Montgomery-Asberg Depression Scale (MADRS), and the International Neuropsychiatric Interview (MINI) was used to exclude comorbid psychiatric disorders. The evolution of depressive symptoms was assessed using the Quick Inventory of Depressive Symptomatology-Self Report (QIDS-SR16). Patients' sleep was evaluated using, Munich Chronotype Questionnaire and with Pittsburgh Sleep Quality Index (PSQI) and sleep agenda. In addition, circadian parameters were assessed using Kronowise ^® device (KW6), and target sleep quality indices were calculated. Results: The intervention combining daylight exposure with pharmacological treatment demonstrated significant improvements in depressive symptoms. There was a noticeable trend towards subjective improvement in sleep quality. Data registered with the KW6 device indicated an improvement in motor activity and peripheral temperature rhythms. Conclusions: Depressive patients undergoing psychopharmacological treatment, who received a specific instruction to increase their exposure to daylight, improved their depressive symptoms, sleep quality, and circadian rhythms.