Blue light emerges as another effective option for seasonal affective disorder

Narrow-band blue light is as effective as bright white-light for the treatment of seasonal affective disorder (SAD), according to a recent study published online ahead of print in the Journal of Affective Disorders.

“Ever since a new photoreceptor was discovered with a highest sensitivity to 470-490 nm blue light, it has been speculated that blue light has some advantages in the treatment of SAD over more traditional treatments,” wrote study authors, led by Ybe Meesters, PhD, University of Groningen, University Medical Center Groningen, The Netherlands.

For 15 days, they studied 45 patients with SAD who completed 30-minute sessions of light treatment administered on 5 consecutive days. In all, 21 patients received treatment with broad-wavelength, white light without UV (10,000 lx, irradiance: 31.7 W/m²), while 24 were treated with narrow-band blue light (100 lx, irradiance: 1.0 W/m²).

Patients completed weekly mood and energy questionnaires, and underwent assessment with the Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorder Version (SIGH-SAD).

Dr. Meesters and colleagues found significantly lower SIGH-SAD ratings in both groups compared with baseline, with a 67% reduction in those treated with blue light and a 73.2% reduction in those treated with white light. Differences between the two groups were not significant.

What is SAD?

SAD is a form of depression related to seasonal changes. According to the American Psychiatric Association, SAD affects about 5% of adults in the United States annually and can last for about 40% of the year. Women are more likely to have SAD than men, and younger adults have it more often than older ones. Other risk factors for SAD include a family history of SAD or other depressive disorders, major depression or bipolar disorder, and living at great distances from the equator.

The causes of SAD are still unknown, but it has been linked to biochemical imbalances in the brain caused by the shorter days and reduced sunlight typical during winter. Circadian rhythm and serotonin and melatonin levels may be important factors, as all are affected by seasonal changes.

Researchers have studied the possible neurobiological causes of SAD, but have yet to find anything definitive.

For example, in another recent study also published in the Journal of Affective Disorders, researchers found that the response of the amygdala in individuals with SAD was significantly less than in healthy controls when shown angry, fearful, or neutral faces, or some combination of them.

Researchers from Denmark also published results from a preliminary study demonstrating that women with SAD with the short 5-HTTLPR genotype had different 5-HTT levels that may predispose them to be more vulnerable to persistent stressors such as winter.

SAD symptomatology

The symptoms of SAD will generally manifest in late fall or early winter and will typically begin as mild in intensity and increase in severity as the season progresses. They can include the following:

• Depressed mood for most of the day, almost every day
• Lost interest in activities that were once enjoyable
• Low energy
• Problems sleeping
• Changes in appetite and weight
• Sluggish or agitated feelings
• Feelings of hopelessness, worthlessness, or guilt
• Difficulty concentrating
• Frequent suicidal thoughts

Fall and winter SAD also have specific symptoms, which include oversleeping, changes in appetite, weight gain, and fatigue. Spring and summer SAD, also known as reverse SAD, can include symptoms of insomnia, loss of appetite, weight loss, and agitation or anxiety.

A diagnosis of SAD, like many other mental disorders, is often difficult because so many other conditions have similar symptoms. Patient exams should include a physical exam, lab test (especially for thyroid function), as well as a psychological evaluation that includes the Diagnostic and Statistical Manual of Mental Disorders-5 criteria for SAD.

Phototherapy is considered first-line treatment for fall-onset SAD, and consists of exposure to bright light within the first hour of waking each day. Light therapy is designed to duplicate natural outdoor light and can induce changes in the chemicals in the brain which are linked to mood. Other therapies include medication and psychotherapy.

Left untreated, SAD can lead to social withdrawal, problems at school or work, substance abuse, other mental health disorders, and even suicidal thoughts or behavior.