Light Therapy in Seasonal Affective Disorder

An Interview with Dr. Michael Terman on the Effects of Light on Mood

Sep 24, 2009

Millions of people dread the arrival of winter and the depression symptoms it brings. But others, who have discovered SAD light therapy, have a different outlook.

Dr. Michael Terman has been studying how light affects behavior and mood in animals and humans for nearly forty years. He conducts scientific research into why millions of Americans experience symptoms like intense carbohydrate cravings, weight gain, low energy and depressed mood in winter, and what can be done about these symptoms of Seasonal Affective Disorder or "SAD."

Suite101's Lisa DeLuca conducted an interview with Dr. Terman concerning the effects of light on a person's mood and mental health.

Winter Blues, Seasonal Affective Disorder (SAD) and Circadian Rhythm

MT: “Later and later sunrise as we go through fall toward winter. It's as simple as that. For the population-as-a-whole, people report feeling their worst months of the year starting at the fall equinox and peaking in January and February…

“Our internal circadian rhythm system is genetically designed to rely on the early morning light signal to stay in sync with local time. When that signal is delayed during the [fall and winter,] the rhythm drifts later… Yet our sleep-wake cycle stays fairly constant because workday hours [don’t change.]”

SAD, Light, and Sleep-Wake Cycles

LD: So you’re saying we still have to force ourselves to wake up at the same time to go to work even though, due to later sunrise, we would be naturally inclined to sleep later?

MT: “Yes. The result: we force ourselves to sleep out of sync with our circadian rhythm, which is a formula for depression.”

LD:. A lot of people seem to hate that it gets dark at 4:30 p.m. in winter and find that depressing. But it sounds like you are saying that the problem is not that there is less light in the 24 hours, just that sunrise is later.

MT: "This would be the conclusion from an extensive set of research studies. Light supplementation in the early morning is very effective, while evening supplementation has far less benefit. Biologically, this relates to the internal circadian clock's specific receptivity to morning light."

LD: If people could get up at whatever time they wanted, would that solve the problem?

MT: "It would reduce the problem to allow human life to swing with the seasons, but not eliminate it."

LD: But why does the sleep-wake cycle take its toll on mood and increase cravings for carbohydrates? Why doesn’t it show up as, I don’t know, aches and pains or a craving for celery sticks or something?

MT: "Biochemically, a carb load acts as a mild stimulant to the serotonin system. You could call it 'nature's Prozac,' but at too low a dose to do much good. So the result is excessive intake with diminishing returns, and the side effect of weight gain -- often 10 to 15 pounds each winter, but sometimes twice that amount."

Risk Factors for SAD: Genetics and Latitude

LD: Many people with SAD have to endure family members who roll their eyes and tell them it’s all in their head. Why don't seasonal light changes affect everyone that way?

MT: “One predisposing factor is genetic vulnerability in two domains: to depression per se, but also to seasonally changing light exposure.

“If you move to the equator, you won't have seasonal changes in light exposure. The data indicate that the problem is entirely absent only below 18 degrees north latitude, the level of Mexico City. If you move from New York to Florida, the likelihood of SAD is greatly reduced, but not eliminated."

Light Therapy for SAD

LD: What can people do to help themselves when suffering from symptoms of SAD?

MT: “Light therapy, as described authoritatively by the non-profit Center for Environmental Therapeutics (CET) should be used as a self-treatment only by people with the winter doldrums. Those with full-blown SAD should do so only under doctors’ guidance and monitoring…The CET developed an online, confidential self-test to measure the degree of seasonal cycling and its severity, and recommend [that people get professional help] if indicated."

Light Therapy is the first-line treatment of choice for SAD and winter blues. These conditions occur in people who live at certain latitudes and have a genetic predisposition for depression or changing light exposure.

The copyright of the article Light Therapy in Seasonal Affective Disorder in Depression is owned by Lisa C. DeLuca. Permission to republish Light Therapy in Seasonal Affective Disorder in print or online must be granted by the author in writing.