Brief report
Morning sunlight reduces length of hospitalization in bipolar depression

https://doi.org/10.1016/S0165-0327(00)00149-XGet rights and content

Abstract

Background: Bright artificial light improves non-seasonal depression. Preliminary observations suggest that sunlight could share this effect. Methods: Length of hospitalization was recorded for a sample of 415 unipolar and 187 bipolar depressed inpatients, assigned to rooms with eastern (E) or western (W) windows. Results: Bipolar inpatients in E rooms (exposed to direct sunlight in the morning) had a mean 3.67-day shorter hospital stay than patients in W rooms. No effect was found in unipolar inpatients. Conclusions: Natural sunlight can be an underestimated and uncontrolled light therapy for bipolar depression. Limitations: This is a naturalistic retrospective observation, which needs to be confirmed by prospective studies.

Introduction

The effectiveness of bright light therapy of depression may be not limited to seasonal affective disorder (SAD) (Kripke, 1998). Natural sunlight might share the clinical effects of artificial light. In SAD, natural light in the morning had the same efficacy of artificial light (Wirz-Justice et al., 1996), and severity of depression negatively correlated with photoperiod (Oren et al., 1994). Daily recordings revealed a relationship between mood, hours of sunlight, and solar irradiation in two non-SAD affective patients (Summers and Shur, 1992, Eagles, 1994). Unmonitored light therapy caused marked mood oscillations (Meesters and Van Houwelingen, 1998), and a strict control of the light/dark cycle improved treatment-refractory rapid-cycling bipolar illness (Wehr et al., 1998, Wirz-Justice et al., 1999).

The orientation of rooms in a Canadian ward provided a 'natural experiment' on the relationship between sunlight and length of hospitalization for depression (Beauchemin and Hays, 1996). Patients in sunny rooms had a mean 2.6-day shorter hospitalization than patients in dimly lit rooms, a difference more marked in men (6.8 days) than in women (0.7 days).

Our ward is favourably situated to replicate and expand this naturalistic observation. In a corridor with rooms on either side, windows are oriented to East or West. Eastern rooms (E) receive direct sunlight in the morning, while western rooms (W) receive it in the evening. Ambient light intensity in the two conditions (avoiding direct sunlight, which reached more than 30 000 lux) showed wide differences: on a bright May day at 09:00 h an E room measured at 15 500 lux, and a W room at 1400 lux, while at 17:00 h an E room measured at 2700 lux, and a W room at 3000 lux; on a day with light clouds values were E=1500 lux and W=150 lux at 09:00 h, and E=200 lux and W=1500 lux at 17:00 h; while in a cloudy day values were E=650 lux and W=150 lux at 09:00 h, and E=140 lux and W=600 lux at 17:00 h.

Artificial bright light therapy has an higher efficacy in the morning (Lewy et al., 1998): if sunlight has the same effect, a difference should be detected between E and W conditions.

Section snippets

Method

We reviewed charts for all admissions for non-psychotic depression over a 3-year period (1996-98) with a diagnosis of major depressive disorder, single or recurrent, or bipolar disorder, depressive episode, moderate or severe (DSM IV criteria), without Axis I codiagnosis and with a length of stay longer than 6 days.

Rooms (E or W) had been randomly assigned based on first available free space. Psychiatrists in charge were the same for E and W rooms. Medications were administered upon clinical

Results

Results are summarized in Table 1.

No significant difference was detected in the unipolar group.

In the bipolar group hospitalization was significantly shorter for E rooms in the whole sample. Significant differences were detected for summer and fall admissions.

Discussion

Only bipolar depressed inpatients exposed to natural sunlight in the morning had an hospital stay shorter than patients exposed in the evening, with no gender effects. Given the sex distribution of unipolar and bipolar disorder, it is possible that the previously reported sex differences on the effects of sunlight (Beauchemin and Hays, 1996) could be due to the effect of the unipolar/bipolar dichothomy.

Bipolar patients showed an increased sensitivity to the biological effects of light (Lewy et

Acknowledgments

We thank Dr Anna Wirz-Justice for precious help during manuscript preparation.

Cited by (222)

View all citing articles on Scopus
View full text