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Randomised, morning by evening light crossover trial balanced by parallel group controls, in addition to a non-photic control (negative air ionisation), with follow up to 4 weeks.
Psychiatry department in New York, New York, USA.
158 patients between 18 and 65 years of age who were recruited through media and physician referrals with a DSM-III-R diagnosis of SAD. Exclusion criteria included other Axis I disorders, suicide attempt within the previous 3 years, and habitual sleep onset later than 1 am or awakening later than 9 am. 145 patients (92%) completed the study.
Patients were allocated to 6 groups for 2 consecutive treatment periods, each lasting 10–14 days. 2 parallel groups received morning treatment with negative ions. 4 groups received light treatment and were crossed over at mid point using the following sequences: morning-evening, evening-morning, morning-morning, and evening-evening (10 000 lux, 30 min/d). 2 groups received negative air ionisation treatment at either high density (2.7 x 106) or low density (serving as the placebo control, 1.0 x 104 per cubic centimeter) (high-high and low-low sequences, 30 min/d in the morning). All treatments lasted for 20–28 days with a 1–3 week withdrawal phase.
Main outcome measure
Symptom severity assessed using the Structured Interview Guide for the Hamilton Depression Rating Scale-Seasonal Affective Disorder Version (SIGH-SAD).
Data are reported for the 124 patients who relapsed or who remained depressed during the withdrawal to ensure that clinical improvement was not caused by spontaneous remission. Patients in the light treatment and the high density negative air ionisation treatment groups improved in percentage change scores on the depression scale. Bright light in the morning or evening and high density negative ions led to clinically important relief with >50% reduction in depressive symptoms in at least half of the patients receiving the treatment (table⇓). Remission (defined as a SIGH-SAD score of ≤8 after treatment) rates were higher in the morning light, evening light, and high ions groups compared with the low ions group at week 4, and in the morning v evening light comparison (table⇓).
Bright light and high density negative ionisation reduced depressive symptoms in patients with seasonal affective disorder.
In general, the treatment of winter depression (or SAD) is similar to that of other forms of affective disorder except that bright light exposure has been recommended as the first line treatment option (the administration of visible light producing the intensity of at least 2500 lux towards the face). Indoors, at home, the intensity of light measured in front of the eyes of a standing person is typically ≤100 lux, and 300 to 500 lux at the workplace. Outdoors, the level of illumination varies greatly by latitude, season, time of day, and local weather conditions, ranging from about ≤2000 lux on a cloudy winter day to ≥10 000 lux in direct sunshine. A previous overview of controlled trials with 332 patients showed that light of 2500 lux in 2 hour daily morning sessions for 1 week improved 67% of patients with mild, and 40% with moderate to severe episodes of winter depression.1 Recently, the use of higher intensities (up to 10 000 lux) and shorter exposures (down to half an hour) has been reported to yield equally good response rates. Designs of bright light trials have been compromised, however, by a lack of adequate control for placebo and blinding.
The studies by Terman et al and Lewy et al overcome some of these design problems and confirm earlier data which show that bright light treatment is effective and well tolerated in patients with winter depression. The study by Terman et al, together with the results from another recent study,2 gives evidence that morning bright light treatment has an antidepressant effect that is statistically beyond its placebo effect. The benefit of light over placebo is in producing substantially more full remissions. Both studies also pull together conflicting research findings and show that bright light treatment is more effective when given in the morning than in the evening. Another, as yet preliminary, finding reported in the study by Terman et al is the antidepressant effect of high density negative air ionisation.
Why is bright light treatment effective in winter depression? Fixed phase delays in the timing of the circadian clock are suggested to have a key role in winter depression. According to this hypothesis, the efficacy of morning bright light treatment is related to the corrective phase advances. Recent data show, however, that the circadian cycle appears to be more elastic in patients with winter depression compared with healthy people, deviating more from 24 hours and peaking at less regular times.3 Patients with winter depression tend to show an abnormal degree of phase advance during bright light treatment,4 although the necessity of phase advances for clinical efficacy have now been questioned.
There is some evidence that suggests that the resetting of the circadian clock is worsened by the decreasing photoperiod or exposure to cold weather at high latitudes, and with aging. There may also be separate time givers regulating waking up and falling asleep. Information of the direction (decreasing or increasing) and velocity of change of the photoperiod is being transformed into the production of melatonin. This signal might then entrain the 2 timegivers discordantly, predisposing to winter depression, for example, because of irregularities in the circadian clockwork.
The mechanism aside, the studies by Terman et al and Lewy et al provide sound evidence that most patients with winter depression will benefit most from bright light exposure immediately on awakening. In selected patients, the evening bright light treatment can be a preferred alternative. The practice guidelines for the intensity and duration of bright light exposure to optimise the treatment outcome still await further investigation. The study by Terman et al also provides evidence that high density negative air ionisation may have a marked antidepressant effect. This finding awaits replication in future investigations.
Source of funding: National Institute of Mental Health.
For correspondence: Dr M Terman, New York State Psychiatric Institute, 1051 Riverside Drive, Unit 50, New York, NY 10032, USA. Fax +1 212 543 5184.
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