Health Services Research Unit, University of Aberdeen, Foresterhill, Aberdeen
Royal Cornhill Hospital, Cornhill Road, Aberdeen
Correspondence: Simon A Naji, Health Services Research Unit, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, UK. Tel: +44 (0) 1224 551127, fax: +44 (0) 1224 663087; e-mail: sme076{at}abdn.ac.uk
Declaration of interest The study was funded by the Chief Scientist Office of the Scottish Executive Department of Health.
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ABSTRACT |
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Aims To evaluate light therapy in primary care.
Method Fifty-seven participants with seasonal affective disorder were randomly allocated to 4 weeks of bright white or dim red light. Baseline expectations for treatment were assessed. Outcome was assessed with the Structured Interview Guide for the Hamilton Depression Scale, Seasonal Affective Disorder Version.
Results Both groups showed decreases in symptom scores of more than 40%. There were no differences in proportions of responders in either group, regardless of the remission criteria applied, with around 60% (74% white light, 57% red light) meeting broad criteria for response and 31% (30% white light, 33% red light) meeting strict criteria. There were no differences in treatment expectations.
Conclusions Primary care patients with seasonal affective disorder improve after light therapy, but bright white light is not associated with greater improvements.
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INTRODUCTION |
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METHOD |
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Treatments
All participants received light-boxes containing three 36 W bright white
series tubes with either a clear filter, giving bright white light at 10 000
lux (bright white group), or a red filter, giving dim-red light at 500 lux
(dim red group). Investigation of different parts of the light spectrum
suggests that although light at the green/blue end of the spectrum may be
effective, red light is not (Oren et
al, 1991). To determine the correct distance to obtain either
10 000 lux (white) or 500 lux (red), intensities were measured for each
light-box using an illuminometer. The distance between the light-box and the
participants' eyes was generally around 20 inches. Light-boxes were delivered
to and set up for participants, and they were advised that the most beneficial
time of use would be mornings, but that use before 7 p.m. would be acceptable.
They were instructed to use the light-box for 30 min a day for the 1st week,
45 min a day for the 2nd week and up to 1 h a day for the remaining 2 weeks of
treatment. Boxes were positioned on a flat surface, with the participant at an
angle of approximately 30° to the light, with their eyes at midfixture
level. They were instructed not to stare directly at the light but to gaze
across at it once or twice a minute.
Assessment and measures
Participants completed the SIGH-SAD-SR at baseline, weekly during the 4
weeks of treatment, and at 2 and 6 weeks after completion of treatment. During
the treatment phase, participants also rated their mood and energy at the end
of each day on a scale of -10 to +10
(Eagles, 1994). The mean daily
mood and energy levels over each week were used in the analysis.
In order to assess participants' general expectations for light therapy and their specific expectations in respect of their allocated light-box, expectations were measured just before and just after the light-box was set up and switched on, using a four-item expectation questionnaire (Hardy et al, 1995). Briefly, participants were asked to rate, on scales of 1-7, how logical, useful and successful they thought light treatment would be and whether they would recommend it to a friend.
Statistical analysis
The primary outcome variable was response to treatment at 4 weeks, defined
and analysed in three ways: a total SIGH-SAD-SR score of less than or equal to
50% of the baseline total score and a total score of less than or equal to 8
(strict remission criteria); a total SIGH-SAD-SR score of less than 18 and an
atypical score of less than 8 (intermediate remission criteria); and a total
score less than or equal to 50% of the baseline total (broad remission
criteria). The difference in the proportion of responders at week 4 was
estimated, together with 95% confidence intervals for the difference.
Differences between the two groups in continuous data were assessed using
Student's t-test for normally distributed data or the Mann-Whitney
test for non-normally distributed data. Categorical response data were
analysed using the 2-test with Yates correction. The Pearson
correlation coefficient was used to measure the relationship between
continuous variables, and the Spearman rank correlation was used for
non-normally distributed data.
Secondary outcomes included the total SIGH-SAD-SR score at week 4 in an analysis of covariance (ANCOVA) with the baseline SIGH-SAD-SR score as the covariate. A secondary repeated-measures ANCOVA was used to investigate differences between groups in total scores over time (weeks 1-4). Other secondary outcomes included mood and energy levels and expectations.
For the primary outcome, a 5% significance level was used on a two-tailed test, with 95% confidence intervals calculated where appropriate. A 1% significance level on a two-tailed test was used for secondary outcomes. Analysis was by intention to treat. It was estimated that a sample of 41 patients in each group would yield 80% power to detect at the 5% level of significance a 30% difference between the groups in the proportions of responders at 4 weeks.
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RESULTS |
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Expectation ratings
Participants' baseline expectations for treatment prior to seeing the
allocated light-box were not significantly different between the two groups
(Table 1), and were generally
high, with the medians all in excess of the mid-point of 4 for all four
questions. Expectations after allocated light-boxes were seen and switched on
were not significantly different between the two groups
(Table 1).
Response to treatment
Table 2 shows the number and
per cent of participants who met the specified criteria for response to
treatment at 4 weeks. There were no statistically significant differences
between the two light treatment groups when analysed using 2
tests with Yates correction, regardless of the response criteria employed.
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The SIGH-SAD-SR scores
Both groups showed a marked decrease in SIGH-SAD-SR scores, with no clear
differences between the groups (Fig.
1). Both the typical and atypical scores decreased each week by
similar magnitudes, regardless of the treatment group. In the ANCOVA of total
SIGH-SAD-SR scores at week 4, only those with complete data for all time
points were included in the analysis (27 white light and 21 red light,
n=48) (Table 3). There
was no significant difference between the two light treatments in terms of the
total SIGH-SAD-SR scores at week 4. However, in a repeated-measures ANCOVA,
the differences in SIGH-SAD-SR ratings between weeks in the pairwise
comparisons were highly significant (F=20.61, d.f.=3,
P<0.001), confirming both treatment groups' improvement over the 4
weeks of treatment. The overall decrease from week 1 to week 4, calculated
using estimated marginal means, was 48% for white light and 42% for red light.
When the same analyses were repeated for all 57 participants' data, by using
the method of last value carried forward to substitute for any missing values
the results were statistically similar.
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There were no significant correlations between participants' expectation ratings and SIGH-SAD-SR scores at each time point in either group. The correlation between the total expectation score (sum of the four expectation ratings after seeing the allocated light-box) and the degree of change in SIGH-SAD-SR scores from weeks 1 to 4 in the white light group was 0.182 (P=0.363) and in the red light group was -0.237 (P=0.3143).
Daily mood and energy ratings
The mean mood and energy ratings, smoothed using a centred moving average
measurement, are shown in Fig.
2. Both increased over the 4 weeks for both treatment groups.
There was no significant difference between the groups' mean mood or energy
levels at week 4. There was a non-significant trend towards higher ratings of
mood and energy in participants with red-light-boxes. There were significant
inverse correlations between weekly mean mood and energy levels and total
SIGH-SAD-SR scores at each time point (ranging from -0.90 to -0.56,
P<0.01).
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DISCUSSION |
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Comparisons with previous studies
Comparisons between evaluations of light therapy are complicated by
methodological variation, particularly in recruitment methods and eligibility
criteria, whether and which control treatments are employed, whether and how
treatment expectations are measured and in definitions of response to
treatment. None the less, our finding that SIGH-SAD-SR scores at the end of
treatment were significantly reduced after light treatment is consistent with
previous findings, including the two most recently reported randomised
controlled trials (Eastman et al,
1998; Terman et al,
1998). In addition, the SIGH-SAD-SR scores of both treatment
groups in the present study are strikingly similar to those in previous
studies.
It is in the lack of a clear difference between treatment and control groups in the proportions of participants defined as responders or remitters that the current study is not consistent with those recent trials, both of which used negative ion generator controls, in one case deactivated. Using relatively broad criteria, the proportion of responders in treatment and control groups in the current study was around 60%. This rate of broadly defined response to a presumed active treatment for SAD is consistent with the literature, whether to bright white light (e.g. Eastman et al, 1998; Terman et al, 1998) or to fluoxetine (Lam et al, 1995). Indeed, when Eastman et al also used a broad definition, there was no clear difference between bright white light and dummy negative ion control. The application of more stringent criteria in the current study reduced the response rate to bright light to 33% at week 4, which is no better than the response rate to the red light control or the usual placebo response rates in non-seasonal depression (e.g. Eastman, 1990; Brown, 1994; Moncrieff et al, 1998). This is in contrast to the recent (negative ion control) trials where strictly defined response rates to bright light were of the order of 50-65%, which is significantly greater than the control response rates of 30-40%. The current results are more similar to studies of bright light versus dim light controls, often using head-mounted visors, where bright light was not shown to be superior (Joffe et al, 1993; Rosenthal et al, 1993; Teicher et al, 1995; Levitt et al, 1996). In the most recent trial of this type (Meesters et al, 1999), bright white light and infrared light were equally effective and superior to the no-light control condition.
Choice of control or placebo conditions
A review of studies of light therapy, where the control was usually light
of a lower intensity and sometimes a different colour (as in the current
study), concluded that although bright light had been shown to be superior to
the dim light control, such superiority might be little more than a placebo
effect because participants' expectations often predicted response or that
responders had a higher expectation than non-responders
(Terman et al, 1996).
In the current study, treatment expectations were not significantly different
in the two groups and were not correlated with treatment outcome. Although
Eastman et al (1998)
report no difference in expectations between groups, and Terman et al
(1998) report no correlation
between expectation and response, both papers conclude from these findings
that their reported superiority of light therapy is mediated through a
specific antidepressant effect beyond its placebo effect. Our own findings are
not consistent with that conclusion. However, it may be that dim red light
should not be considered as an inactive or inert placebo but as an active
placebo (mimicking all the non-specific effects of an active treatment) or as
an alternative form of active light treatment. The dummy negative ion
generator, with fewer obvious similarities to a light-box, might be considered
an inert placebo. An interpretation in terms of an active placebo might help
to explain why our findings are consistent with earlier studies using
red-light controls and inconsistent with recent studies using negative ion
generator controls, particularly in view of our study population. For example,
it has been shown that depressed participants recruited into trials through
advertising (as in both trials using negative ion generator controls) are more
likely to be placebo responders than those recruited through routine referral
(Miller et al,
1997).
Limitations of the study
The study is limited by the small sample size, resulting in low power to
detect small differences between the groups. None the less, there was a
notable absence of even a non-significant trend towards differences between
participants treated with white and red light. A further limitation in this
and all other studies evaluating light therapy concerns the choice of an
appropriate control, as discussed above. In addition, given the context in
which our study was undertaken, with undiagnosed primary care participants not
receiving specific treatment for SAD and largely unaware themselves that they
had the condition, it can be argued that the appropriate and most pragmatic
control is treatment as usual. However, the application of
treatment within the current trial was highly pragmatic, with participants
supervising their own treatments, as they would in routine clinical practice
in primary care. We did not assess compliance systematically, and it might be
that it was substantially poorer than in previously reported trials with
atypically aware and motivated participants. Thus, despite the fact that many
primary care participants with SAD showed considerable improvements in symptom
scores after 4 weeks of light therapy, larger open trials with carefully
selected control conditions and long-term follow-up are needed to provide
further evidence about the effectiveness and efficiency of light therapy for
SAD in primary care, and these should include assessments of the impact upon
the documented high service use of sufferers.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication June 5, 2000. Revision received October 18, 2000. Accepted for publication October 27, 2000.