By Jennifer Copley (Last Updated 31 August 2008)
Seasonal Affective Disorder, or S.A.D., is a depressive condition with symptoms that worsen during the darker fall and winter months. The causes of S.A.D. are not fully understood, though it’s believed to result from reduced production or uptake of serotonin (a neurotransmitter that helps regulate mood) when there’s less bright light exposure. Hormonal disruption and the effects of colder winter temperatures on circadian rhythms have also been suggested as potential contributors.
Symptoms of Seasonal Affective Disorder
Common S.A.D. symptoms include:
- Sleeping longer
- Daytime tiredness
- Increased appetite and/or weight gain
- Social withdrawal
- Carbohydrate and sugar cravings, particularly in the afternoon
S.A.D. symptoms usually decrease or disappear in the spring or when the sufferer travels closer to the equator. There is also a far less common summer version of S.A.D. that causes insomnia, irritability, anxiety, and appetite loss.
Light therapy is a treatment commonly used for winter S.A.D. It’s usually administered using a 10,000 lux light box, a smaller “light book,” or visor.
How Light Therapy Works
Light therapy involves sitting in front of a light box, usually for 20 to 30 minutes each day, during the fall and winter months, ideally at the time of day when the person tends to feel most sluggish. This will be the morning for some and the early evening for others. It’s not advisable to use a light box late at night, as it may cause insomnia.
Duration and timing of light exposure may be adjusted as necessary because individual responsiveness will vary. Different durations or frequencies may be required depending on time of year and other factors. People may choose to use their light boxes for two shorter sessions rather than one long session each day either for convenience or because they find the split dose more effective.
To receive the full benefits of light therapy, users should have their eyes open, as eye exposure is superior to skin exposure. Brighter lights work better than dimmer lights, and morning light provides greater benefits for the majority of people (though not all). However, evening light provides superior effects to those of a placebo, even in people who respond better to morning light therapy.
Effectiveness of Light Therapy for S.A.D.
Benefits of light therapy usually occur anywhere from 48 hours to 2 weeks after daily treatment has been initiated. In various studies, at least 50% of those with S.A.D. have experienced some benefits, and in some cases up to 75% have achieved symptom relief.
Light therapy is particularly effective for S.A.D. sufferers who crave carbohydrates or sweets in the afternoon, and those whose depressive symptoms diminish when they travel to warmer climates. People who suffer from psychic anxiety (psychological agitation or distress) are more likely to respond positively to light therapy than those with somatic anxiety (physical symptoms such as panic attacks). However, light therapy may be beneficial for some people who suffer from panic disorder, particularly if their symptoms tend to worsen during the fall and winter months.
To increase the effectiveness of light therapy, there are complementary strategies that can be implemented, including:
- Getting 60 minutes of aerobic exercise each day
- Taking a walk outside every day when it’s light out
- Sitting near windows in the daytime whenever possible
- Keeping to a regular sleeping and waking schedule
- Engaging in cognitive-behavioural therapy
Light Therapy Side Effects
Side effects of light therapy, which are usually mild if they occur, include:
- Eyestrain or dry eyes
- Jitteriness or nervousness
These side effects can usually be eliminated by placing the light box further away during treatment or reducing the duration of daily exposure. Insomnia can often be prevented by using the light box in the morning rather than at night.
Hypomania or even mania may occur in susceptible individuals, but this side effect is less common, and is more likely in those using light therapy to treat non-seasonal depression rather than S.A.D. Research thus far has not found any adverse effects on the retina from using light therapy.
Although light therapy is relatively safe for most people, it may interact adversely with certain conditions and medications, including:
- Skin conditions that cause photosensitivity
- Photosensitizing herbs or medications, such as Psoralen, St. John’s Wort, and certain antidepressants
- Retinal diseases such as retinitis pigmentosa or macular degeneration
While such conditions don’t necessarily rule out the use of light therapy, it’s important to exercise caution and obtain medical advice before proceeding. You should consult a doctor who is aware of your medical history and any medications you’re currently taking before beginning light therapy.
Obtaining a Light Box
Making your own light device is not recommended, as it may emit the wrong amount of light. Commercially available light boxes are usually safer and more effective than home-made devices. Light boxes cost anywhere from $150 and $500, depending on the size and design.
Research suggests that visiting a tanning salon provides no antidepressant benefits, and ultraviolet (UV) rays increase the risk of skin cancer, so it’s a good idea to choose a light box that filters out UV rays. It’s light intensity rather than full-spectrum exposure that generates benefits for S.A.D. sufferers, so UV is not necessary.
For more health articles, see the main Mind/Body Health page.
This article is provided for informational purposes only and is not intended as a substitute for medical advice. Those with mental or physical health concerns should consult a medical professional.
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