For those suffering from seasonal affective disorder (SAD), the disdain towards winter goes far beyond wet socks from slushy sidewalks.  Winter depression grips its victims on an annual basis from about mid-October through March.  Symptoms range in severity, but generally include low energy, irritable mood, fatigue, and strong cravings for carbohydrates, making weight gain common.

Why so SAD?

The cause of SAD is not fully understood, but is most likely due to a combination of factors associated with low light.  Winter means shorter days and more time spent in doors, which equates to less sun exposure.  We really begin to understand the relation between SAD and light when we look at rates of occurrence as we traverse north from the equator.  At the equator, where the days and temperature stay constant throughout the year, there is virtually no SAD.  The further north you go, the days on average become shorter and colder during the winter months, and rates of SAD rise correspondingly.  One study found that the rate of SAD in the southern USA (Florida) is 1%, compared to 10% in the northern USA (New Hampshire) (1).

Insufficient Light Disrupts Brain Function

Humans may not produce energy from sunlight, but we have more in common with the plant kingdom than most realize.  Numerous sunshine modulating processes occur in the body.  In fact, the pattern of daily functional changes that occur in the body, called the circadian rhythm, uses light as a major indicator for what is occurring outside.  The brain detects light levels in the environment through the retina of the eyes, and changes hormonal expression in the body reflexively.  It makes sense that in low light the body will produce hormones associated with sleepiness, whereas in bright light, it produces hormones associated with wakefulness.

But what happens when there is a disparity between the environmental cues the brain receives and the tasks necessary to fulfill your day?  Things get out of whack!  When the circadian rhythm is disrupted the biochemical environment of the body becomes confused, and negative symptoms can occur.  This type of disruption is particularly the case in SAD, where low light exposure means hormones of sleepiness are being produced during daytime hours, making us irritable, fatigued, and even depressed.

Inappropriate secretion of melatonin is believed to play a major role in the development of SAD.  Melatonin, a hormone produced in dim light by the pineal gland, is supposed to rise in the early evening hours to elicit sleepiness, peaking around midnight, and falling towards the morning to permit wakefulness.  Because of low light exposure in winter months, people with SAD have excessive melatonin levels during the day (2).

The involvement of serotonin in SAD is also suspected.  Serotonin is a neurotransmitter that stimulates the body during the day.  At night time, serotonin is converted to melatonin.  Thus, when melatonin is being produced incorrectly during the day, it can lead to serotonin deficiencies.  People with SAD are found to have a lower than normal level of daytime serotonin (2).  It is for this reason that antidepressant (SSRI) medications have been shown to help treat severe SAD, and are used as a foundation treatment by medical doctors (3).

Becoming Less SAD

Treatment of SAD focuses on providing the body what is necessary to establish a properly functioning circadian rhythm, and making life more tolerable when feeling down.

Light Therapy

If the natural environment is not providing you with enough light to keep your bio-rhythms stable, you should make an artificial environment that does.  Light therapy is perhaps the most important therapeutic intervention for those suffering from SAD.  It greatly reduces depressive symptoms, and even corrects winter hormone imbalance (4).  And luckily, the days of sitting in front special full spectrum lamps at set times of the day are over.  A person can fill their environment with sunshine mimicking light by simply putting full spectrum bulbs in to their living spaces (workplace, home), which are readily available in the marketplace.  Take ultimate control of your environment by simulating the entire day.  Surround yourself in full light from waking until 6pm, and then gradually dim the light to darkness at 10pm.  This will ensure your circadian rhythm is producing the correct hormones at the correct times, without restricting normal activity.


If you have read the article up until now, you may be surprised to learn that taking supplemental melatonin will improve SAD.  It comes down to timing.  Having melatonin levels too high at the wrong time can be detrimental, whereas having high melatonin at the right time can be corrective.  A dose of melatonin prior to bed, when levels are meant to be rising, will keep your circadian rhythm on tract (5).


5-Hydroxytryptophan is an amino acid compound that is a precursor to both serotonin and melatonin.  Because it modulates the hormones associated with SAD, it has potential benefit in more severe depressive symptoms, especially when used in conjunction with light therapy.  Anyone taking SSRI medications should seek help to find out whether 5-HTP is a safe treatment for them.

Vitamin D

Because vitamin D is sunshine dependent  most people with SAD are vitamin D deficient (review:  Preventing Vitamin D Deficiency).  While the research is not definitive, it appears that vitamin D supplementation may be beneficial for the treatment of SAD.

Running Away from Depression

Literally, run.  Or do anything active.  Daily aerobic exercise is repeatedly shown as one of the most effective ways to regulate the circadian rhythm, treating and preventing depression.

Seek Help for Depression

The discussion above describes the more prevalent and milder subsyndromal variety of SAD.  Symptoms of depression that can accompany severe seasonal affective disorder including hopelessness, social withdrawal, and suicidal ideation are very serious.  People suffering from depression should seek help from a qualified health practitioner immediately, as many effective treatment options exist.

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Works Cited

1. Prevalence of seasonal affective disorder at four latitudes. Rosent, L, Targum, S and Terman, M. 2, 1990, Psychiatry Research, Vol. 31, pp. 131-144.

2. Diurnal and seasonal variations of melatonin and serotonin in women with seasonal affective disorder. Danilenko KV, Putilov AA, Russkikh GS, Duffy LK, Ebbesson SO. 1994, Arctic Med Res, pp. 137-145.

3. Seasonal Affective Disorder: A Guide to Diagnosis and Management. Partonen, T and Lonnqvist, J. 1998, CNS Drugs, pp. 203-212.

4. Evidence of a Biological Effect of Light Therapy on the Retina of Patients with Seasonal Affective Disorder. Lavoie, M, et al., et al. 2009, Biological Psychiatry , pp. 253-258.

5. Circadian uses of melatonin in humans. Lewy, A, et al., et al. 2006, Chronobiol Int, pp. 403-412.