Health and Medicine Question #305

Anonymous, a 45 year old female from the Internet asks on December 15, 1997,

How does light therapy work for people with SAD (Seasonal Affective Disorder)?

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The answer

Sean Dukelow answered on December 15, 1997

We don't understand the hormone regulatory process fully. The links between the brain chemicals melatonin and serotonin are not clear at all. Serotonin is a derivative of melatonin and we know that light suppresses melatonin production. How this affects SAD isn't really known.

Recently, light therapy has been shown to improve the condition of many SAD patients. Unfortunately, there is no conclusive evidence as to how light therapy effects changes in SAD patients. There are a number of plausible hypotheses though. The first theory is that people with SAD have a disturbance in their circadian rhythm (biological clock). The brain secretes hormones that affect sleep and mood and the winter may affect the secretion of these hormones. A second theory is that there are problems with the chemical transmission within the brain. Levels of serotonin and dopamine (brain chemicals known as neurotransmitters) may be imbalanced in people with SAD and light therapy may help alleviate this imbalance. A third is that patients with SAD have reduced light sensitivity and this might be corrected by light therapy. (see The UBC Mood Disorder Centre website for more information). Originally it was thought that full spectrum light (light which includes ultraviolet) was necessary to alleviate symptoms of SAD. More recently studies have shown the UV light is not necessary and that white fluorescent light is just as effective in alleviating the symptoms of SAD. Light therapy seems to work in many cases. It is possible to build your own light box if you are handy and this could probably do as good a job as a commercially available device. A quick online search will provide you with many different companies that make light boxes.  If you suspect that you or someone you know has SAD, it is a good idea to consult your personal physician to have a diagnosis made. You might wish to discuss the possibility of light therapy or drug therapy or a combination of the two.

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