The effects of bright light treatment via ear canals on quality of sleep and depressive mood among overworked employees: A randomized-controlled clinical trial

Abstract

BACKGROUND:

Many overworked employees need tools to improve their depressive mood or sleep disorder. In Finland, a new device of bright light therapy was developed.

OBJECTIVE:

Our objective was to evaluate the effect of bright light treatment via ear canals on improving the depressive mood and sleep disorder.

METHODS:

We conducted a randomized, controlled, crossover designed, open-label trial. We examined 27 participants aged 23–52 years, assigned to either Early treatment or Later treatment groups. The Early treatment group used the device on weekdays for the first 4 weeks, followed by a 4-week observation period. The Later treatment group had an observation period for the first 4 weeks, followed by device treatment for the subsequent 4 weeks. Every Friday, the participants were asked to answer questionnaires: A Self-rating Depression Scale (SDS), an Athens Insomnia Scale (AIS), and a Profile of Mood States (POMS) Brief Form.

RESULTS:

While no significant effect was found on the SDS following treatment (p = 0.16), the AIS showed a significant improvement (p = 0.004), and the scores for the Depression (D) and Vigor (V) of POMs decreased significantly (p = 0.045, p = 0.006, respectively).

CONCLUSIONS:

Bright light treatment via ear canals may improve sleep quality and depressive mood.

Keywords

Bright light device mental health overworked employees IT company clinical trial

1 Introduction

Globally, depressive disorders are common mental disorders in people of all ages. The Global Burden of Disease identified depressive disorders in 2017 as a leading cause of burden [1, 2]. Depressive disorders reduce social functions and working efficiency of employees, further cause comorbidity with a physical disorder [3, 4]. Therefore, to reduce the burden of depressive disorders, the prevention of this mental health problem would need to be allocated as a national public-health policy, and a new cost-effective intervention would need to be developed [1 –5].

Bright light therapy is one of the treatment methods for seasonal affective disorder [6 –11]. During the last 30 years, bright light therapy has expanded to treat chronic depression, premenstrual depression, bipolar depression, and disturbances of the sleep-wake cycle [6]. In Finland, a unique intervention study has suggested that bright light therapy via ear canals for approximately 10 minutes per day over 4 weeks could improve depressive symptoms [12, 13]. In this treatment method, the subject uses a small portable device, which is a simplified version of the conventional bright light therapy. We consider that it would be particularly beneficial for improving the mental condition of overworked business persons with depressive symptoms. However, in previous studies, subjects were patients with seasonal affective disorders, and the evaluation of its effects has been limited to depression scales [12, 13]. Furthermore, these previous results might not be applicable to other populations. Therefore, to evaluate the effects of bright light therapy via ear canals on depressive symptoms in more detail, we conducted a randomized, controlled, crossover designed trial. We measured insomnia symptoms and total mood conditions, as we expected that these indices would allow an observation of the effects of this therapy.

2 Methods

2.1 Participants

The participants were volunteers who belonged to an information technology (IT) company in Tokyo, Japan. An occupational nurse recruited the participants through office advertisements. The selection criteria were as follows: 20 years of age or older, demonstration of mild to intermediate degrees of depression symptoms in the Self-rating Depression Scale (SDS) questionnaire at pre-screening, and provision of written informed consent before entry. The exclusion criteria were as follows: patient of psychiatry, patients with serious levels of depression at pre-screening requiring medication, pregnancy, and engagement in breastfeeding, or if the occupational physician judged the individual to be inadequate for participation in this study. Thirty-four employees applied for participation, one applicant did not participate in the informed consent session, four were excluded by the SDS pre-screening test because of their low scores, and two were excluded by the occupational physician’s judgment; 27 people aged 23–52 years (17 males and 10 females, age of 33.8±5.3) were enrolled in this study. The sample size was determined based on the previous study [11]. Since the previous one-arm clinical trial study showed the positive effects among 13 participants, this study aimed to obtain more than 26 participants for each group. During this study, one participant dropped out (Fig. 1).

Fig. 1

Sampling scheme of the study.

2.2 Study design

We conducted this study using a randomized, controlled, open-labeled, crossover design. Twenty-seven participants were randomly divided into the Early or Later treatment groups within the strata of sex, age, and SDS scores at pre-screening with the use of an SAS program survey-select procedure. The participants used the bright light device for 12 minutes per day during the 4-week treatment period. Considering overworked businessmen with depressive symptoms are the potential target of this treatment, and the rental and use of the device would thus be confined to weekdays, the treatment was administered between Mondays and Fridays. During the first 4 weeks, the Early treatment group was treated, while the Later treatment group underwent the observation period. A one-week interval was set as the wash-out period, and in the following 4 weeks, the roles were switched between the groups. Participants were directed not to change their lifestyles during this trial.

2.3 Bright light device and treatment

We used a non-invasive photon application device, a VALKEE^® bright light device (Valkee Ltd., Oulunsalo Finland) [12, 13], which was approved as a medical device in the European Union on March 30, 2010. It was specially designed to target bright light treatment directly towards the brain via ear canals using light-emitting diodes attached to earplugs. The light intensity at the end of both light guides in the ear canals was 8.5 lumens.

2.4 Outcomes

To evaluate the subjective mental status, the participants answered the self-administered questionnaires every Friday. The baseline was the Friday before the start of the treatment. The indices for outcomes were as follows: 20 questions with the Self-rating Depression Scale (SDS) for evaluating depressive symptoms [14], eight questions with the Athens Insomnia Scale (AIS) for evaluating insomnia symptoms [15], and 30 questions of the Profile of Mood States (POMS) Brief Form for evaluating total mood [16]. Since the main outcome in this study was the effect on depressive symptoms, we measured SDS as the primary endpoint. In addition, we measured insomnia symptoms because recent research has suggested that normal bright light therapy may affect sleep disorder [5]. As a secondary endpoint, we also measured total mood conditions, which may interact closely with depression [16]. We classified the eight AIS questions into two categories: five questions about “quality of sleep” and three questions about “daytime sleepiness” [14].

2.5 Statistical analysis

We statistically analyzed changes in the scores of SDS, AIS, and POMS between the treatment and observation periods. The statistical method applied a linear mixed model for repeated measures analysis using all available observed data. Results with p < 0.05 in the two-sided test were considered statistically significant. All statistical analyses were performed with SAS software (version 9.4; SAS Institute Inc., Cary, NC, USA).

2.6 Ethics approval

All methods were performed in accordance with the Ethical Guidelines on Biomedical Research Involving Human Subjects of Japan. This study was approved by the Institutional Review Board of the Ehime University Hospital and registered as UMIN Clinical Trial Registry “UMIN 000012611”. Written informed consent was obtained from the participants.

3 Results

Table 1 shows the baseline characteristics of the participants. There was no significant difference between the Early and Later treatment groups in any index. Table 2 indicates the SDS, AIS, and POMS scores in the Early and Later treatment groups for every week. No significant effect was evident in the SDS scores following the bright light treatment via ear canals (p = 0.16). As shown in Figs. 2a and 2b, while a significant improvement was shown in the AIS scores for the “quality of sleep” category following the treatment (p = 0.004), an improvement was not observed in the “daytime sleepiness” category (p = 0.097). In the POMS categories, the scores for Depression (D) and Vigor (V) decreased significantly (p = 0.045, p = 0.006, respectively). The scores for other POMS categories showed no significant changes. During this study, we observed no serious side effects caused by the bright light treatment via ear canals.

Table 1
Baseline characteristics of participants

The Early treatment group (n = 14) The Later treatment group (n = 13) P ^*

Men 9 8

Age (years) 33.6±7.2 34.0±4.2 0.85

SDS score 56.3±11.3 54.6±6.7 0.64

AIS score 6.1±3.3 4.8±3.8 0.35

POMS score

Total Mood Distrubance (TMD) 25.1±20.1 19.2±15.4 0.41

Tension-Anxiety (T-A) 7.7±4.6 6.2±3.7 0.37

Depression (D) 5.1±5.2 4.4±3.3 0.66

Angry-Hostility (A-H) 3.9±3.2 3.4±2.1 0.61

Vigor (V) 7.1±4.8 7.1±5.8 0.998

Fatigue (F) 8.8±4.4 6.9±3.4 0.23

Confusion (C) 6.6±4.0 5.4±2.7 0.37

	The Early treatment group (n = 14)	The Later treatment group (n = 13)	P ^*
Men	9	8
Age (years)	33.6±7.2	34.0±4.2	0.85
SDS score	56.3±11.3	54.6±6.7	0.64
AIS score	6.1±3.3	4.8±3.8	0.35
POMS score
Total Mood Distrubance (TMD)	25.1±20.1	19.2±15.4	0.41
Tension-Anxiety (T-A)	7.7±4.6	6.2±3.7	0.37
Depression (D)	5.1±5.2	4.4±3.3	0.66
Angry-Hostility (A-H)	3.9±3.2	3.4±2.1	0.61
Vigor (V)	7.1±4.8	7.1±5.8	0.998
Fatigue (F)	8.8±4.4	6.9±3.4	0.23
Confusion (C)	6.6±4.0	5.4±2.7	0.37

Values are expressed as mean±standard deviation. SDS; Self-ratin Depression Scale, AIS; Athens Insomnia Scale, POMS; Profile of Mood Status. ^*Wilcoxon rank sum test.

Table 2

Changes in outcomes from the baseline to week 9

	The Early treatment group (n = 14)										The Later treatment group (n = 13)										P ^*
	Treatment					Observation					Observation					Treatment
	0 w	1 w	2 w	3 w	4 w	5 w	6 w	7 w	8 w	9 w	0 w	1 w	2 w	3 w	4 w	5 w	6 w	7 w	8 w	9 w
SDS	56.3 (11.3)	54.8 (9.1)	55.1 (11.8)	51.7 (11.5)	51.8 (10.6)	50.5 (10.7)	51.4 (10.1)	51.7 (11.6)	52.7 (11.5)	52.0 (11.8)	54.6 (6.7)	56.9 (8.3)	53.9 (7.4)	54.2 (7.5)	52.8 (8.1)	52.6 (8.1)	50.1 (8.9)	51.8 (7.4)	51.6 (6.7)	49.5 (7.7)	0.16
AIS	6.1 (3.3)	5.0 (2.1)	5.1 (2.6)	4.1 (2.9)	3.4 (1.8)	4.1 (2.7)	5.6 (2.6)	4.9 (2.4)	5.3 (2.4)	5.1 (2.5)	4.8 (3.8)	6.4 (3.9)	5.6 (3.5)	5.8 (3.9)	5.8 (3.4)	6.5 (4.0)	4.9 (3.4)	5.2 (2.8)	5.3 (3.3)	4.8 (3.4)	<0.01
Quality of sleep	3.9 (2.4)	3.1 (1.5)	2.9 (1.8)	2.3 (1.6)	1.9 (1.4)	2.5 (1.3)	3.5 (1.8)	3.0 (1.6)	3.3 (1.5)	3.1 (1.7)	2.7 (2.9)	3.2 (2.7)	3.3 (2.4)	3.5 (2.4)	3.8 (2.2)	3.9 (2.7)	2.8 (2.3)	3.0 (2.1)	3.0 (2.3)	3.0 (2.5)	<0.01
Daytime sleepiness	2.2 (1.5)	1.9 (1.0)	2.2 (1.3)	1.8 (1.6)	1.4 (1.0)	1.6 (1.7)	2.1 (1.5)	1.9 (1.3)	2.0 (1.8)	1.9 (1.5)	2.2 (1.7)	3.2 (2.1)	2.3 (1.8)	2.4 (1.9)	2.0 (1.4)	2.6 (1.7)	2.2 (1.6)	2.2 (1.0)	2.3 (1.2)	1.8 (1.3)	0.10
POMS-TMD	25.1 (20.6)	19.0 (20.4)	17.2 (17.1)	15.3 (16.6)	11.9 (16.0)	14.4 (20.2)	15.2 (22.7)	14.6 (23.3)	15.7 (22.3)	13.6 (22.3)	19.2 (15.4)	25.1 (14.8)	24.5 (15.6)	16.6 (18.7)	19.6 (16.9)	24.5 (16.7)	22.4 (14.7)	20.0 (12.4)	16.6 (10.8)	15.0 (14.7)	0.67
TA	7.7 (4.6)	5.9 (3.8)	6.2 (3.8)	5.0 (3.6)	4.4 (3.5)	5.4 (4.4)	6.0 (5.5)	5.9 (5.0)	5.5 (4.4)	5.9 (4.5)	6.2 (3.7)	7.1 (3.6)	6.6 (3.3)	5.7 (4.0)	6.4 (3.1)	6.8 (3.7)	6.5 (3.3)	5.8 (3.6)	5.3 (4.3)	6.3 (5.8)	0.18
D	5.1 (5.2)	3.6 (3.7)	3.6 (3.3)	3.1 (3.5)	2.4 (2.7)	3.4 (3.8)	3.4 (4.3)	3.4 (4.9)	3.2 (4.0)	2.7 (3.9)	4.4 (3.3)	5.5 (3.0)	5.5 (3.2)	3.8 (3.6)	4.8 (4.1)	4.9 (4.0)	4.2 (3.4)	4.3 (4.1)	3.5 (3.1)	2.6 (2.4)	0.04
AH	3.9 (3.2)	3.6 (4.3)	3.4 (3.5)	2.6 (2.6)	2.4 (2.6)	2.8 (3.0)	3.2 (5.3)	2.5 (3.9)	3.0 (3.7)	2.5 (3.9)	3.4 (2.1)	4.7 (3.1)	4.2 (3.0)	3.1 (2.6)	3.2 (2.2)	4.4 (3.6)	4.5 (3.3)	3.3 (2.6)	3.2 (2.6)	2.3 (1.7)	0.99
V	7.1 (4.8)	7.4 (5.1)	7.1 (4.1)	7.3 (5.0)	8.2 (4.2)	8.6 (5.4)	8.6 (5.9)	8.2 (6.1)	8.8 (4.5)	8.7 (6.2)	7.1 (5.8)	6.4 (5.7)	7.1 (5.2)	7.5 (6.3)	7.3 (6.2)	5.7 (5.2)	5.9 (5.2)	5.8 (4.8)	5.9 (4.6)	7.2 (5.5)	<0.01
F	8.8 (4.4)	7.5 (4.8)	6.2 (3.4)	6.1 (4.0)	5.6 (4.2)	6.1 (3.4)	5.9 (3.9)	5.5 (4.1)	6.8 (4.4)	5.7 (3.9)	6.9 (3.4)	7.7 (3.6)	8.1 (4.3)	6.0 (4.0)	6.3 (4.3)	7.4 (3.6)	6.8 (3.5)	6.3 (3.1)	5.2 (3.2)	6.1 (4.5)	0.52
C	6.6 (4.0)	5.8 (3.8)	4.9 (3.7)	5.7 (2.6)	5.3 (2.4)	5.5 (3.9)	5.4 (3.8)	5.6 (4.2)	5.9 (4.4)	5.5 (4.2)	5.4 (2.7)	6.5 (3.0)	7.2 (3.4)	5.5 (3.2)	6.2 (1.9)	6.7 (2.6)	6.3 (2.5)	6.1 (2.1)	5.4 (2.0)	5.0 (2.3)	0.31

Values are expressed as mean±standard deviation. TMD; Total Mood Disturbance, TA; Tension-Anxiety, D; Depression, AH; Anger-Hostility, V; Vigor, F; Fatigue, C; Confusion. ^*The effects of intervention (treatment) were analyzed by mixed model repeated analysis.

Fig. 2a

Changes in “quality of sleep” scores in the Early and Later treatment groups. Black line is the Early treatment group and gray line is the Later treatment group. Straight line denotes the treatment period and dotted line denotes the observation period.

Fig. 2b

Changes in “daytime sleepiness” scores in the Early and Later treatment groups. Black line is the Early treatment group and gray line is the Later treatment group. Straight line denotes the treatment period and dotted line denotes the observation period.

4 Discussion

This study highlighted the effects of bright light treatment via ear canals on the subjective symptoms of depressive mood, the symptoms of sleep disorder, and mood profiles. While no significant effect was found in the SDS scores, the AIS scores and the D scores of the POMS categories showed significant improvements. By following up with the participants in the wash-out period (weeks 4 to 9 of the Early treatment group), we observed a different trend in the carry-over effects on sleep disorder and depressive mood.

The unique effect in this study was the response at early stages on “quality of sleep.” In the Early treatment group, only the 1-week treatment decreased the “quality of sleep” score, which returned to the pre-treatment baseline value following only 2 weeks of treatment (Table 2, weeks 4 to 6). On the other hand, the D scores of the POMS seemed to improve significantly and maintained the effects for 5 weeks following the treatment (Table 2, weeks 4 to 9). The change in the AIS score, which would mean improved sleep conditions, appeared to improve the D score of POMS. Several previous studies have reported that poor-quality sleep, such as chronic sleep deprivation and sleep apnea, causes depression [17 –20]. In this study, the V scores of the POMS categories decreased significantly (Table 2), indicating that participants’ vigor decreased following treatment, which could be a result of the calming influence of improving a depressive mood. In addition, as shown in Table 2, the V scores increased in the last week of treatment (from weeks 3 to 4 in the Early group, from weeks 8 to 9 in the Later group), thus suggesting that vigor returned after a period of calm.

Considering the functions of photosensitive brain proteins, bright light treatment via ear canals might affect depressive mood without improving sleep disorder. Despite the scarcity of reports on this topic [12, 21], photopigment melanopsin would play a key role in mediating the non-visual effects of light as well as modulating the circadian rhythm [22, 23], which suggests a potential underlying mechanism. However, when the brain recognizes bright light directly through the ear canals, it is uncertain exactly whether melanopsin operates through the same pathway as when light is recognized through the eyes [12, 21].

The strength of this study lies in our verification of the effects of bright light treatment via ear canals on the symptoms of depressive mood and sleep disorder for company employees by using a randomized, controlled, crossover design, which provided us with robust evidence.

We should refer to the several limitations of the present study. First, since this study was an open-labeled trial, the findings might include some placebo effects. Second, we evaluated only self-administered questionnaires. However, every questionnaire that we had chosen for this study had already been validated and used by previous research, although they were subjective questionnaires [24, 25].

Compared to the employees of other occupations, depressive symptoms or administrative leave from mental health problems are common among employees of IT companies, such as the participants in this trial, due to their day-to-day overwork and stress (The report of Ministry of Health, 2013). We showed the effects of bright light treatment via ear canals for busy and stressful employees in a simple and convenient way. Moreover, this treatment appears to be a more cost-effective option for employees compared to conventional bright light therapy. Future trials should be conducted on a larger scale, which may lead to the development of more efficient treatment methods, such as evaluating objective measurements, treating during the daytime, or using a monochromatic short-wavelength “blue light.”

5 Conclusions

The present study showed that bright light treatment via ear canals can be a useful tool for improving the quality of sleep and depressive mood symptoms of the employees of an IT company.

Conflict of interest

None of the authors had a personal or financial conflict of interest.

Funding

This study was supported by funding from Smart-medical Corporation (Tokyo, Japan). Smartmedical was the distributing agent of the VALKEE^® device until August 2018, not a manufacturer. Smartmedical had no commitment in the data analysis and interpretation.

Footnotes

Acknowledgments

We are grateful to the participants and the company staff, especially Ms. Tomoko Tsuyuki, for their cooperation in this study.

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