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Initial Response to Light Therapy Doesn’t Predict Outcome

Initial Response to Light Therapy Doesnt Predict OutcomePatients’ initial responses to light therapy for seasonal affective disorder (SAD) may not indicate how much it ultimately helps them, according to a researcher from Baltimore University in Baltimore, Md.

Monika Acharya, M.D., speaking at the American Psychiatric Association’s annual meeting in Philadelphia, said that in a placebo-controlled study of 79 patients with SAD, the correlation coefficient for outcomes after one hour compared with outcomes after six weeks was close to zero.

Yet patients’ symptoms declined noticeably from baseline, both after the first session and at the end of the treatment course, she noted.

Early responses to treatment for many medical conditions can predict mid- to long-term outcomes, Acharya said. Biological changes from using light therapy for SAD are detectable immediately, suggesting that patients’ initial response could predict those who would benefit from continued treatment.

Previous studies have found that nearly half of SAD patients do not respond to light therapy.

Acharya’s study included 79 patients, about two-thirds female, with a mean age of 44. They were diagnosed with SAD through structured clinical interviews; none of them was taking psychotropic medications. They were randomly assigned to an initial two-hour session of bright white light or red light (the red light being the placebo).

Following the initial session, all patients then used white light one hour every morning for six weeks.

Patients followed up weekly by phone with clinic staff and reported their responses. Side effects and the duration and timing of treatment could then be addressed, Acharya said.

Depression symptoms were evaluated primarily with a SAD-specific form of the Hamilton Depression Rating Scale, the SIGH-SAD form. All patients had baseline scores over 20 (mean 32.3).

The first treatment led to small reductions in SIGH-SAD scores in both the white- and red-light groups: 1.6 points with white light (P=0.03) and 0.8 points with red light (P=0.20).

After 4 weeks, mean scores had dropped to 12.7, and by week six they had declined further to an average of 8.3.

Sixty-three percent of patients were responders and 31 percent had symptoms resolved by week four. After another two weeks of treatment, 82.1 percent had responded and 58 percent were in remission, according to Acharya.

But responses after one hour and after six weeks were not correlated at all, Acharya reported, irrespective of whether they were assigned to red or white light at the first session. Nor was a 20 percent reduction in SIGH-SAD scores after the first session — seen in nine participants — significantly associated with remission at four or six weeks.

On the other hand, she and her colleagues found that body mass index did correlate significantly with response: Patients with a higher BMI had greater responses to the light therapy.

The study’s flexible dosing was a significant limitation, Acharya said. No data was available on whether there was a relation between outcomes after the first session or at later evaluations and patients’ dosing patterns during the trial.

Source: American Psychiatric Association

Initial Response to Light Therapy Doesn’t Predict Outcome

Candace Czernicki

APA Reference
Czernicki, C. (2018). Initial Response to Light Therapy Doesn’t Predict Outcome. Psych Central. Retrieved on October 28, 2020, from
Scientifically Reviewed
Last updated: 8 Aug 2018 (Originally: 7 May 2012)
Last reviewed: By a member of our scientific advisory board on 8 Aug 2018
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