Using Bright Light Therapy to Avoid Seasonal Affective Disorder

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What is Winter Depression?

Winter depression or seasonal affective disorder (SAD) is a syndrome characterized by recurrent depressive episodes which occur during the winter. The onset may begin as early as September or October and the symptoms spontaneously remit in April or May. Individuals suffering from winter depression typically do not experience depressive symptoms during the summer.

Recent studies indicate that more than 10 million Americans suffer from winter depression and many more experience "winter doldrums," a lesser form of winter depression. On average, women are three times more likely than men to suffer from winter depression.

Symptoms of Winter Depression

• Sadness
• Irritability
• Fatigue
• Apathy
• Increased appetite
• Weight gain
• Carbohydrate craving
• Decreased physical activity
• Increased sleep
• Difficulty in awakening.

What Causes Winter Depression?

Many of the functions of the human body follow a daily (circadian) rhythm which is close to 24 hours in duration. Circadian rhythms are regulated by the body's internal clock and by exposure to sunlight, which synchronizes the body's clock to the 24-hour day.

We believe that winter depression occurs because of a decrease in the amount of light that persons receive during the winter months. Winter days are considerably shorter, and frequent cloud cover reduces exposure to sunlight. Reduced sunlight and/or shorter days may result in some of the body's circadian rhythms becoming out of synch with each other, which may trigger the depression.

Treatment with Bright Light

Currently, bright light therapy is the treatment of choice for winter depression. Numerous studies have demonstrated that bright light therapy is safe and effective. However, there still is some disagreement as to how light therapy works and more research needs to be done to understand and improve this form of treatment.

If you would like to be treated with bright light, we strongly recommend that you consult your doctor and be supervised by your doctor during treatment. People respond differently to bright light exposure; it is important that bright light therapy be timed correctly so that you will benefit from this treatment. Also, some medications can make you more sensitive to light. Individuals with retinal problems should have an ophthalmological exam before beginning light therapy.

What Type of Light Works?

We recommend using a light fixture which is able to produce diffuse light of at least 2500 lux at about 3 feet away from the source. Higher intensity lights (10,000 lux) are also available, which reduce the amount of exposure time needed.

Our studies are showing minimal differences between full spectrum and ordinary "cool white" fluorescent lamps. Therefore, we are currently recommending "cool white" fluorescent lamps because they contain less ultraviolet radiation, which some physicians recommend avoiding. [Note: Importantly, some full spectrum light therapy systems/bulbs are now designed so as to deliver no harmful UV rays.]

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The Human Circadian System [an explanation of terms & concepts]

Circadian rhythm: Simply put, "circadian rhythm" means daily cycle. "Circadian" comes from Latin: circa = approximately, and dies = day.

Many bodily functions and behaviors have a circadian rhythm: The most obvious circadian rhythm is the sleep/wake cycle. Body temperature and the secretion of various hormones (insulin, cortisol, and melatonin) have circadian rhythms. Cognitive performance and mood also have been found to be synchronized by circadian rhythms.

The circadian rhythm of melatonin: Melatonin is a hormone made by the pineal gland in the brain and is normally produced at night. Melatonin plays a role in the regulation of the body clock by acting as a darkness signal to the body. When melatonin is produced, the body knows it is time to get ready for sleep.

The endogenous circadian pacemaker: This is the biological clock that regulates all circadian rhythms. The endogenous circadian pacemaker is located in the suprachiasmatic nucleus (SCN) of the hypothalamus in the brain. The SCN is normally entrained (synchronized) to a 24-hour cycle by time cues in the environment, mainly by the 24-hour light-dark cycle in sighted people. Light in the eyes is the primary synchronizer of the biological clock.

Circadian rhythm disorders: In circadian rhythm disorders, there is a mismatch between the timing of the sleep/wake rhythm and the desired (or required) time for sleep.

Examples of circadian rhythm disorders include winter depression (Seasonal Affective Disorder, or SAD), jetlag, shift work maladaption, advanced sleep phase syndrome, delayed sleep phase syndrome, and 24-hour sleep/wake schedule disorders (like those associated with free-running circadian rhythms). [See also "Reset" Your Disrupted Internal Clock Naturally – Using a Dawn-Dusk Simulator.]

Free-running circadian rhythms: About 15% of the legally blind have no light perception at all. The majority of totally blind individuals have abnormal, free-running circadian rhythms, meaning that their internal body clock drifts to a different time each day. Although free-running blind individuals may try to maintain normal sleep and wake time, they typically have recurrent bouts of nighttime insomnia and daytime sleepiness as their body clocks drift out of sync with the 24-hour day. This problem is one of the primary complaints in some blind individuals. The recurrences of such symptoms can be precisely predicted through circadian rhythm (specifically, melatonin rhythm) assessments.

* This information is reproduced with kind permission of the OHSU Sleep & Mood Disorders Laboratory in Portland, Oregon – an internationally-recognized center of research on melatonin, circadian rhythms, and disorders related to the body clock since 1982. For information about the lab, its current projects and published research, and for contact information, click here.

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Note: This information has not been evaluated by the FDA. It is not meant to prevent, diagnose, treat, or cure any illness, condition, or disease. It is very important that you make no change in your personal healthcare plan or health support regimen without researching and discussing it in collaboration with your professional healthcare team.

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