The Importance of Light in Seasonal Affective Disorder and the Possible Role of Melatonin

Depression is one of the most prevalent mental disorders in our society. In 1999, the World Health Organization reported depression as being "the leading cause of disability" (Kaufman, 1999). According to a CDC study conductedduring the 2005-2006 term, it was found that "in any 2-week period, 5.4% of Americans 12 years of age and older experienced depression" with rates even higher in mid to older Americans 40-59 years of age. This rather high rate, combined with untold numbers of unreported cases, puts depression in the U.S an a highly unacceptable rate. One of the lesser reported types of depression is called seasonal affective disorder or seasonal depression. This form of depression is rather tricky, as prevalence of it increases during the winter months, and experiences higher rates in colder, darker regions of the U.S, and the world. Biologically, seasonal affective disorder is associated with what is humorously called the Dracula hormone, or more scientifically, melatonin.

Before delving deeper into this particular topic of interest, it's important to evaluate what exactly seasonal affective disorder is. First of all, depression is not classified by sadness alone. We often describe our sadness at a situation or circumstance as "depression;" however, in many cases, we're simply explaining typical down or blue feelings associated with an upsetting event (Comer, 2005). This isn't depression. Depression describes the persistent, severe, and lengthy feeling of sadness, hopelessness, and lack of motivation.

The American Psychiatric Association's DSM-IV (2000) details the diagnostic checklist of an individual that would be labeled as depression. In order for an individual to be classified as clinically depressed, they must exhibit at least five of the symptoms listed, within a two week period; which include, but are not limited to: insomnia or hypersomnia, depressed mood most of the day, fatigue or loss of energy, significant weight loss or weight gain, reduced ability to think and concentrate, and markedly diminished interest or pleasure in daily activities (American Psychiatric Association, 2000). In addition, they also must exhibit "significant distress or impairment" (American Psychiatric Association, 2000). So, as you can see, depression isn't a simple "I feel sad" diagnosis.

Seasonal affective disorder is categorized by the American Psychiatric Association as seasonal patterns of major depressive episodes (Saeed & Bruce, 1998). Thus, an individual with seasonal affective disorder would exhibit the same symptoms of depression as those listed above, but experience them seasonally, during the cold, dark, winter months. Additionally, it is typical to see full remission of depressive symptoms as "characteristic" times of the year (Saeed & Bruce, 1998), such as summer.

There are a number of theories presenting different ideals on how and why depression happens, but for the purpose of this article we'll be focusing on a biological viewpoint, most specifically melatonin as a catalyst for seasonal depression.

What is Melatonin?

Melatonin is a naturally occurring hormone found in the brain. It plays a critical role in regulating the body's natural clock, or circadian rhythm (University of Maryland Medical Center, 2011). Melatonin is produced and secreted in greater mass during the evening and nighttime hours, thus allowing an individual to sleep. During the early morning hours melatonin secretion significantly lowers causing wakefulness. When melatonin levels follow this typical pattern, an individual exhibit's a normal sleep-wake cycle, as you would see in the average person. However, melatonin regulation isn't as simple as following basic times of the day. Evidence suggests that light plays a significant role in when, and how much, melatonin is secreted (Comer, 2005). When the light is low, for example on rainy, overcast days, the level of melatonin secretion goes up causing the type of drowsiness one might experience at night, even in the middle of the night.

Melatonin and Seasonal Affective Disorder

The discord between when melatonin is supposed to be secreted, and when melatonin is actually secreted can lead to seasonal affective disorder, especially in individuals who live in parts of the world where there is a significant amount of dark days during the year. Julie Smith Riley of Seattle's Swedish Hospital notes that individuals at highest risk for seasonal affective disorder or SAD are located in the northern latitude where light is hard to come by during the fall, winter, and spring seasons (2011). Seattle is a prime example, and well-known for it's drowsy, cold, and overcast weather most of the year. Other areas of interest in the U.S have similar weather, like New England.

Some psychologists argue that melatonin does not cause SAD, however, due to the clear correlation between circadian rhythms and the prevalence of melatonin and lack thereof, due to light patterns, seems to suggest that melatonin does in fact play a role in SAD symptoms. It is important, however, to note that melatonin disrupts circadian rhythms and plays it's role in SAD that way; but there are other brain chemicals that have recently been connected to SAD as well. This does not mean that we can underestimate the power that melatonin and proper circadian rhythm regulation plays in SAD and in remedying symptoms. Comer (2009) notes that clinicians are still working on melatonin related treatments, such as melatonin pills to properly regulate levels that are found to be irregular in SAD patients.

Treating Seasonal Affective Disorder with Light

One way to directly treat SAD is by light. As mentioned earlier, the onset of morning light triggers the decrease in melatonin levels in the brain causing wakefulness, and the lack of light during the day can cause premature secretion of melatonin, thus triggering drowsiness, and over time depressive symptoms. The importance of light cannot be understated.

However, it is also important to know that simple at-home lights, and in-passing daylight, is not enough to kick SAD. Most people in high-risk northern latitude locations simply do not get enough light during the day. During the winter, days and days of overcast skies and the effect that darkness can produce cannot be reversed by a mere one day out of the week that the sun shines. Furthermore, at home lights aren't enough to reduce or reverse SAD either. Instead, psychologists and psychiatrists specializing in SAD treatment turn to specially crafted light boxes that can be used at home or at work. These boxes provide the user with a powerful ray of light, specifically "10,000-lux" that is "directed toward the patient at a downward slant" (Saeed & Bruce, 1998). These boxes are designed to mimic the type of light one would get outside, and thus provide the body with the natural light that would typically regulate circadian rhythms. For this reason, the Mayo Clinic (2010) suggests that using the light box in the morning can yield greater results. Other researchers suggest light therapy as most effective "2.5 hours after the midpoint of sleep," which is typically around six hours after the onset of melatonin (Lamberg, 2001) However, discussing the perfect time for you with a professional may be best if SAD symptoms are serious.

Lamberg (2001) discusses the effect of the light box on melatonin during a study saying that "subjects' bedtime and wake-up time remained constant," but "morning light therapy shifted baseline melatonin onset earlier (that is, advanced) on the 24-hour clock by up to 2.65 hours. Evening light therapy delayed it - that is, shifted it to a later clock time - by up to 2.8 hours. The greater the advance in melatonin onset, the greater a patient's improvement." While the article also notes the uncertainty of melatonin as a specific reason for SAD improvement, these findings seemed to indicate that it played a role, if even a small one, since its shifted onset saw improvements in those receiving therapy.

Conclusion

While melatonin's role may still be uncertain, what is certain is that our little "Dracula Hormone" is, in fact, affected by light, and that light affects one's mood drastically. The use of melatonin to regulate otherwise off sleep schedules (circadian rhythms), and the use of light therapy to treat irregular melatonin and mood disorders caused by irregular brain chemistry simply cannot be underestimated. Our bodies not only crave light, they need it to function correctly and regulate mood, keeping us healthy, happy individuals.

References:

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders: DSM-IV-TR. Washington: American Psychiatric Association, 2000.

Comer, R.J. (2009). Abnormal Psychology, 7^th Ed. MacMillan Publishers.

Lamberg, L. (2001). Researchers Identify Best Times for Effective Light Therapy. Psychiatric News 36(6); 28.

Kaufman, M (1999). White House Decries Stigma: "A Health Issue - No More and No Less." Washington Post.

Pratt, L.A & Brody, D.J. (2008). Depression in the United States Household Population, 2005-2006. NCHS Data Briefs, Center for Disease Control and Prevention.

Riley, J.S. (2011). Seasonal Affective Disorder (SAD).

Saeed, S.A. & Bruce, T.J. (1998). Seasonal Affective Disorders. American Family Physician. American Academy of Family Physicians.

University of Maryland Medical Center (2011). Melatonin.