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Seasonal affective depression, triggered by the waning daylight of autumn, is a well-known phenomenon. It turns out that bright lights, however, help depression any time of year.

Adding light therapy significantly increases the benefits of taking antidepressants, researchers have found, and light therapy alone is more effective than just taking a medication for major depression.

For decades, doctors have recommended exposure to strong sunlight or strong sun lamps every morning as a treatment for seasonal affective disorder. Causing depression nearly anywhere north or south of 40 degrees latitude, seasonal affective disorder is an annual onslaught of fatigue, weight gain, insomnia, and bad mood triggered by waning daylight through the autumn months.

Disruption of Melatonin, not Serotonin

Many treatments for non-seasonal affective disorder focus on changing the brain’s use of a mood-related hormone called serotonin. The selective serotonin reuptake inhibitors are medications, such as Prozac, that keep serotonin from being absorbed into neurons, keeping it in the gaps between them so it can play a role in transmitting electrical impulses from neuron to neuron in the brain. The more electrical traffic in the brain, the theory goes, the less depression.

Seasonal affective disorder, however, seems to be caused by a different process. When the eyes sense the visible blue light that is found in sunlight, the brain stops making a substance called melatonin. When the eyes don’t sense blue light, the brain makes the sleep-inducing hormone. The problem with waning daylight hours in autumn is that the brain starts making melatonin earlier and earlier every evening, and stops making melatonin later and later every morning. The result is that people feel sleepy. Their circadian rhythms are thrown off. They don’t have the energy they need for work in the morning, or social activities at night, and “honey I have a headache” becomes the rule for their sexuality.

Treating Seasonal Affective Disorder with Bright Light

Since the problem in seasonal affective disorder is not enough life, the solution, for many people, is more light. It can be enough to go outside for an hour every morning before 9 o’clock if there is bright winter sun. In much of the higher latitudes, however, fall skies tend to be overcast, and by November or December in the Northern Hemisphere or February or March in the Southern Hemisphere, the sun is not completely up for several hours after it’s time to get going for the day.

To deal with this problem, doctors often prescribe the  use of a device called a light box. The purpose of the light box is make sure the eyes have the sensation of full sunlight. The light used for this treatment does not have to be especially bright. As little as 2,000 lux (somewhere between full daylight and bright sun) is enough to make a difference.  Some light boxes provide 10,000 lux (the equivalent to a sunny day). Bright light stops the production of melatonin, which prevents sleepiness, which aids in all the social interactions and personal decisions that lead to less depression. However, it isn’t just seasonal affective disorder that can be treated with bright light therapy.

Continue reading after recommendations

  • Bechtel W. Circadian Rhythms and Mood Disorders: Are the Phenomena and Mechanisms Causally Related? Front Psychiatry. 2015 Aug 24. 6:118. doi: 10.3389/fpsyt.2015.00118. eCollection 2015. Review. PMID: 26379559.
  • Lam RW, Levitt AJ, Levitan RD, Michalak EE, Morehouse R, Ramasubbu R, Yatham LN, Tam EM. Efficacy of Bright Light Treatment, Fluoxetine, and the Combination in Patients With Nonseasonal Major Depressive Disorder: A Randomized Clinical Trial. JAMA Psychiatry. 2015 Nov 18:1-9. doi: 10.1001/jamapsychiatry.2015.2235. [Epub ahead of print]. PMID: 26580307.
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