Light Therapy

Therapeutic Mechanism of Light Therapy

• The exact therapeutic mechanism of light therapy is still unclear. 

• Blood levels of the hormone melatonin are rapidly reduced by light exposure.  Depending on when bright light is presented, the body’s internal clock shifts ahead or is delayed when stimulated by light (Sohn and Lam, 2005).

• Whether or not melatonin plays a role in the patient’s response to light or serves only to mark body time is not yet known.  One theory is that these physiological time shifts may be the basis of the therapeutic response.  Another theory is that the antidepressant effect may not involve rhythm shifts, but rather overall changes in neurotransmitter activity (Sohn and Lam, 2005).

• Light Therapy used at the right time on the biological clock can induce rapid remission in 80% of people with SAD (Terman and  Terman, 2001).

• In 2005 meta-analysis of randomized, controlled trials of light therapy, the American Psychiatric Association found the results “[suggestive] that bright light treatments… for SAD and... non-seasonal depression are efficacious, with effect sizes equivalent to those in most antidepressant pharmacotherapy trials”  (Golden, et al, 2005).

• A study, funded by the Canadian Institutes of Health Research, study compared the use of fluoxetine hydrochloride (Prozac®) to that of light therapy over 5 weeks.  Both groups showed equivalent major improvement in depressive symptoms (Lam and Levitt, 2006). 

• This study was refined in an 8-week multicenter replication, and the results were similar.  The study was headed by Dr. Raymond Lam, Head of the Division of Clinical Neuroscience, Department of Psychiatry at the University of British Columbia and Director of the Mood Disorders Clinic at UBC Hospital. 

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