The effect of light therapy on depression in adults with intellectual disabilities.

Two bright light boxes will be compared with care as usual and with each other in their treatment-effects of depressive symptoms. Participants will be randomly assigned to one of the study groups. Participants assigned to one of the two light therapy groups will receive two weeks of light therapy in the morning. Depressive symptoms will be studied before the start of the two week period of light therapy, directly after the period of light therapy and four weeks after the period of light therapy. The group with care as usual will be monitored with the same time intervals. Stress (cortisol) and circadian rhythm will be studied prior and after light therapy in the two groups who receive light therapy. Participants will be recruited in the Netherlands.

A major depressive disorder is a common mental disorder in the general population. It has major influence on functioning in daily life. Depression can lead to cognitive, social and physical problems and has a negative impact on the quality of life. In the general population, depression may be associated with the mergence of a number of physical illnesses and disrupted circadian rhythms. Also in adults (¡Ý18 years) with intellectual disabilities, depression occurs frequently and this has a negative impact on their daily functioning. Regular treatments for depression, such as cognitive behavioural therapy, can only be used among a small proportion of people with intellectual disabilities. As a result, the current treatment options for adults with intellectual disabilities are often limited tot lifestyle changes and pharmacological treatment. In the general population, light therapy is an effective intervention for both seasonal and non-seasonal depression. However, little is known about the effect of light therapy in depressed people with intellectual disabilities. The study results in the general population can not be merely generalized to adults with intellectual disabilities, because light therapy can have a different effect due to brain injuries (prenatal, perinatal of postnatal), congenital malformations, syndromes, genetic abnormalities and environmental variables.

The purpose of the current study is to investigate the effects of light therapy with two different light boxes on depression in people with intellectual disabilities (IQ ¡Ü 70) compared with care as usual.

- T0: Prior to two week period of light therapy. Completion of three depression questionnaires and the PAS-ADD interview in group I, II and III. Collection of first salvia sample in group I and II. Completion of expectation questionnaire in group I and II. Start of four days of actigraphy in group I and II.

- During light therapy: compliance of light therapy is registered in a log. Start of second period of four days of actigraphy in group I and II at the end of the two week period.

- T1: Directly after two week period of light therapy. Completion of three depression questionnaires in group I, II and III. In case of a major depression at T0 the PAS-ADD interview will be completed for participants of group I, II and III. Collection of second salvia sample in group I and II.

- T2: Completion of three depression questionnaires in group I, II and III. Four days of actigraphy in group I and II.

- 8 weeks after T0: collection of hair sample in group I and II.

Participants will be randomly divided into three groups:

- Group I: this group will receive two weeks of morning light therapy (30 min with 20 cm distance or 60 min with 30 cm distance) with a 10.000 lux bright white light device.

- Group II: this group with receive two weeks of morning light therapy (30 min with 20 cm distance or 60 min with 30 cm distance) with a bright white light device of 100 to 499 lux.

- Group III: this group continues their regular care with no additional intervention.