Effectiveness of Light Therapy Across Seasons

Geestelijke Gezondheidszorg Eindhoven (GGzE)212 enrolled

Overview

This study investigates whether the antidepressant effects of bright light therapy (BLT) differ between the spring/summer season and the autumn/winter season in adults with depressive disorders. While BLT is an established treatment for seasonal affective disorder, increasing evidence suggests it may also be effective for non-seasonal depression. However, it remains unclear whether its effectiveness depends on seasonal variation in natural daylight exposure. In this prospective study conducted in a routine clinical care setting, patients referred for depressive symptoms and a score of \> 6 on the Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-SR) receive BLT in a structured "Light Café" environment. Participants undergo daily morning light therapy sessions (30 minutes at 10,000 lux) for at least one week, with possible extension up to three weeks based on treatment response. A delayed-start design is used, where a subset of participants begins treatment two weeks later, allowing comparison with the natural course of depressive symptoms. Depressive symptoms are assessed using the QIDS-SR at baseline, during treatment, and at follow-up (6 weeks and 3 months post-treatment). Sleep quality, chronotype, circadian timing, and side effects are also measured. The primary objective is to compare the effectiveness of BLT across seasons. Secondary objectives include evaluating the persistence of treatment effects, assessing the change in sleep quality and day-to-day sleep-wake pattern, and exploring whether outcomes vary by chronotype, circadian phase, and patient characteristics. This study aims to inform whether BLT should be considered a year-round treatment option for depressive disorders and to better understand factors influencing individual treatment response.

Study Type

OBSERVATIONAL

Enrollment

212

Conditions

Depression Unipolar Depression

Eligibility

Sex: ALLMin age: 18 Years

Medical Language ↔ Plain English

Inclusion Criteria: * Adults aged 18 years or older * Diagnosis of a depressive disorder (unipolar or bipolar), including both seasonal and non-seasonal depression * Currently indicated for bright light therapy * QIDS-SR score ≥ 6 at baseline * Able to provide informed consent * Sufficient proficiency in Dutch or English to complete questionnaires Exclusion Criteria: * Current (hypo)manic or mixed episode * Current psychotic episode * Severe suicidal ideation requiring immediate intervention * Diagnosis of dementia * QIDS-SR score ≤ 5 at baseline * Age \< 18 years * Inability to provide informed consent * Insufficient language proficiency to complete study questionnaires * Initiation, dose change, or switch of antidepressant medication within 3 weeks before or during light therapy * Long-term use of agomelatine Relative Contraindications (require consultation with treating physician before participation): * Pregnancy (first trimester) * Diabetes or other systemic vascular diseases * Eye conditions associated with increased light sensitivity * Epilepsy Medication-Related Considerations: * Participants are advised not to start antibiotics during light therapy (existing courses should be completed prior to participation) * Participants are advised to discontinue use of photosensitizing medications or topical agents during treatment * Participants are asked to discontinue melatonin use during light therapy * A wash-out period of 1 month is required after discontinuation of melatonin or short-term agomelatine use before starting light therapy

Outcomes

Primary Outcomes

Change in depressive symptom severity (QIDS-SR)

Depressive symptom severity is assessed using the Quick Inventory of Depressive Symptomatology - Self-Report (QIDS-SR), a validated 16-item questionnaire with total scores ranging from 0 to 27 (higher scores indicating greater symptom severity). The primary outcome is the change in QIDS-SR score from baseline (pre-treatment) to end of light therapy. The analysis compares changes between participants treated in the spring/summer season and those treated in the autumn/winter season, while accounting for the delayed-start control condition.

Time frame: Baseline to end of treatment (approximately 1-3 weeks after initiation of light therapy)

Secondary Outcomes

Sustained change in depressive symptoms (QIDS-SR follow-up)

Time frame: End of treatment to 6 weeks and 3 months post-treatment

Change in sleep quality (PSQI)

Sleep quality is measured using the Pittsburgh Sleep Quality Index (PSQI), a validated self-report questionnaire with total scores ranging from 0 to 21 (higher scores indicating poorer sleep quality). The outcome reflects change in sleep quality following light therapy.

Time frame: Baseline to 6 weeks and 3 months post-treatment

Chronotype (MEQ)

Chronotype is assessed using the Morningness-Eveningness Questionnaire (MEQ). This outcome examines whether baseline chronotype moderates changes in depressive symptom severity following light therapy.

Time frame: Baseline (chronotype assessment), end of treatment (1-3 weeks after initiation of light therapy), 6 weeks post-treatment, and 3 months post-treatment

Adverse Events and Side Effects

Side effects are assessed using a self-report questionnaire capturing the presence and severity of common light therapy-related symptoms (e.g., headache, eye irritation, sleep disturbances).

Time frame: At the end of each treatment week, up to 3 weeks

Change in Sleep-Wake Pattern during treatment

Sleep timing, duration, quality and fragmentation, are assessed using a shortened sleep diary based on the Consensus Sleep Diary. This outcome evaluates changes in sleep patterns during light therapy and their relation to treatment response. Participants completed the diaries in the clinic on Mondays and Fridays, reporting retrospectively on their sleep during the preceding nights (i.e., Friday-Sunday nights for Monday entries and Monday-Thursday nights for Friday entries).

Time frame: Twice weekly during treatment, up to 3 weeks