The present study aimed at investigating dynamic ambient bedroom lighting effects in moderately to severely depressed patients at the beginning of inpatient treatment using wrist actigraphy and data from patients’ medical charts. As expected, the bedroom lighting system significantly increased morning (from 6:25h to 7:00h) and decreased evening and nighttime light exposure (from 20:00h to 6:25h) compared to standard bedroom lighting. In addition, we observed sleep-related and circadian activity rhythm effects generated by the dynamic ambient bedroom lighting system. Those effects were likely not caused by differences in pharmacological and non-pharmacological inpatient treatments in the two intervention groups.
Under dynamic lighting, the timing of sleep phases was altered. Patients generally woke up earlier by 20 minutes and, with a delay of one week, also started sleep 33 minutes earlier. Moreover, and independent of treatment time, depressed patients showed shorter waking periods during nighttime sleep by 15 minutes under dynamic lighting and slept 11 minutes longer in treatment week 1 and 27 minutes longer in treatment week 2.
Sleep disturbances are highly prevalent in patients with depressive disorders. Research has also shown a bidirectional association between sleep disturbances and depression45. Thus, improving sleep at the beginning of treatment is of high importance46.
In a recently published review which summarized effects of antidepressants in depressed patients, Tazawa and colleagues47 could show that a successful pharmacotherapy is accompanied with sleep-related effects such as shortened sleep onset latency and increased sleep efficiency (i.e., reduced nighttime activity levels and waking periods). In the present study dynamic lighting generated acute sleep-related effects within the first two inpatient treatment weeks.
Research further showed that depressive disorders are associated with circadian disturbances such as a delayed circadian rhythm48. In addition, a delayed peak in daytime activity is typically found in phases of acute depression49. One suspected mechanism of action of morning light therapy is its potential to phase advance the circadian system2. This effect has already been shown in people with seasonal affective disorder50. However, to date there is inconclusive evidence that phase shifting of circadian rhythms is the mechanism of action in the treatment of non-seasonal depression1.
In the present study, with some delay (in the second treatment week), the onset times of the daily most active and less active periods were earlier under dynamic bedroom lighting indicating that the intervention not only has influenced nighttime sleep but also circadian activity rhythm parameters. It should be mentioned, however, that sleep problems and circadian disturbances are mutually dependent51 and thus reported light effects on the circadian activity rhythm can hardly be separated from light effects on nighttime sleep parameters.
Our study found no effects on inter-daily stability and intra-daily variability of activity rhythms, which is in line with results from a systematic review of Burton and colleagues52. It can be assumed, that hospitalization and consequently the social rhythm imposed to patients’ daily activities may have masked potential light effects on the stability and variability of daily physical activity cycles.
Altered physical activity is a core feature of depression46 and depressed patients often show lower daytime activity levels49,52 and a damped circadian activity profile46. During the course of treatment, these physical activity parameters usually improve52. We found similar results in our study. Irrespective of bedroom lighting, patients’ daytime physical activity level and their daily activity rhythm amplitude improved over time, indicating a general inpatient treatment response.
In this study, patients under dynamic and standard bedroom lighting were prescribed equivalent daily doses of antidepressant and antipsychotic medication. Moreover, by controlling for group differences at the first treatment day, both groups also did not differ in sedative medication across the fourteen treatment days.
It is well documented, that only about half of all depressed patients respond to antidepressant medication and about one third experience remission of symptoms53. Moreover, clinical response to antidepressant medication can often be observed after weeks54, which is problematic for adherence, particularly because significant side effects of antidepressant medication (e.g., digestive problems, appetite disturbances, sleep problems, dizziness, or agitation) frequently occur from the beginning of pharmacotherapy. Consequently, supplementary interventions with a fast antidepressant response are needed.
For a more immediate relief of specific symptoms in depressed patients (e.g., distress, sleeplessness and restlessness), sedatives and antipsychotics are additionally prescribed55,56. It was recently shown, that a combined therapy (benzodiazepines + antidepressants) improve depression severity in the early phase of treatment (1-4 weeks) compared to antidepressants alone57. In addition, benzodiazepines ameliorate symptoms of insomnia efficiently. However, administration must be balanced judiciously against possible harms58.
There are also well recognized non-pharmacological interventions with immediate response in antidepressant treatment, such as electroconvulsive therapy59 and partial or total sleep deprivation60. However, these treatments are complex and can also have significant side effects. Due to its fast-acting response profile, light therapy has been discussed as further, well-tolerated treatment option for depressed patients6. The most recently published meta-analysis confirms the effectiveness of light therapy in non-seasonal depression but also states that more research is needed in severely depressed patients61. The present study, for the first time, provides initial evidence of a fast response in physical activity parameters of depressed inpatients to ambient light treatment.
We did not observe an intervention effect on the length of hospitalization. To date, research has clearly shown that increased sunlight exposure during the day reduced inpatient treatment duration in severely depressed patients62–65. It can be hypothesized that in our study the light intervention took place at a different time of day and thus may have not affected the length of hospitalization. Further studies are warranted to substantiate this assumption.
This study has several limitations. First, sample size was small. Although we included 58 patients in our study, only data from 30 subjects could be analyzed. Main cause of the high drop-out rate was the fact, that the wrist-worn actimeter was not well accepted. Moreover, a few patients reported that the actimeter disrupted nighttime sleep. Second, no further objective and subjective sleep measure (e.g., polysomnography, questionnaires) nor circadian phase marker (e.g., melatonin or core body temperature) were recorded to confirm results obtained from wrist actimetry. Third, self-rated depression symptoms were recorded at admission only. Fourth, actimetric data were only available after admission. However, by analyzing actimetry data within the first three treatment days, we could not observe differences in sleep parameters between the two intervention groups.
To conclude, in this pilot study first beneficial effects of dynamic bedroom lighting (artificial dawn and dusk and blue-depleted nighttime lighting) on inpatients with moderate to severe depression were reported. The light intervention showed fast-acting effects on sleep and circadian activity rhythm parameters which cannot be explained by differences in medication, non-pharmacological treatments and daytime light exposure. Reported effects indicate that ambient bedroom light may have significant short-term effects in inpatient treatment of persons with major depression. Results further complement research on light therapy in non-seasonal depression. Larger studies are warranted to confirm results from this pilot study and to establish dynamic ambient lighting as an effective additional treatment option.