What causes Seasonal Affective Disorder (SAD)? How do you treat it?


When fall arrives in the Pacific Northwest, it comes wrapped in a dark, gray, wet blanket. 

Take one quick look outside. Yes, unfortunately, the dark season is here.

We've all got names for the general drop in energy and enthusiasm we experience to some degree when the seasons change:

"winter depression," "winter blues," "seasonal depression," "cabin fever."

All of these nods to the "dark season" acknowledge a very real mood disorder for many who live in our latitude: seasonal affective disorder (SAD). Not everyone who lives in northern climates suffers from SAD, but it is still prevalent. SAD is triggered by changes in natural light during the fall and winter that alter the circadian system. It has been shown to measurably alter both behavior and biology for an estimated three to ten million people worldwide. 

What is Seasonal Affective Disorder?

The American Psychiatric Association added SAD to its manual of mood disorders nearly 30 years ago as a seasonally specific condition legitimately falling along the spectrum of depressive disorders.


Some people are significantly affected by the onset of SAD, to the point that they struggle with the simple activities of daily life that others manage without any problem.

It's a confusing disorder to identify, diagnose, and treat, as well. Sleep and depression are not mutually exclusive concerns. Many can confuse the symptoms of SAD with the symptoms of depression.

The one thing that binds together both conditions, however, is sleep disruption. 

SAD: The Symptoms

Top of the list of SAD symptoms is hypersomnia, defined as excessive sleep of nine or more hours a night. Eight out of 10 SAD sufferers complain of this kind of ongoing malaise related to hypersomnia

While it's not unusual for human beings to adopt a "hibernation" mode during the fall and winter and sleep longer (let's face it: it's hard to get out of bed when it's dark, cold, or rainy outside), people with SAD regularly oversleep by an extra two hours a night and still feel tired all the time.


Research shows that those with SAD have less sleep efficiency, less time in deep restorative sleep, and more REM density than their nonSAD counterparts; SAD seems to have a body-wide influence over sleep architectureand cannot be blamed as simply "not wanting to get out of bed."

Ten percent of people with a SAD diagnosis also suffer from insomnia; meanwhile, another subgroup of sufferers endure a combination of both hypersomnia andinsomnia. Studies show that sudden-onset insomnia that occurs around the time between the autumnal equinox and the change to daylight saving time may help to distinguish SAD from a more straightforward insomnia diagnosis

SAD shares many symptoms with other forms of depression, which complicates matters. The symptoms shared by both SAD and clinical depression include:

What causes SAD?

Circadian rhythm shifts are at the heart of problems with depression and sleep patterns during the beginning of the "dark season."

Hormone dips 

Human circadian rhythms typically align with the Earth's light and dark cycles. These normal reductions in natural light along the latitudes closer to the poles can trigger reduced levels of serotonin, for one thing.

Serotonin is a key mood-regulating neurotransmitter. Less serotonin circulating in the system can result in depressive symptoms. 

In addition, a person who has SAD may also struggle to release enough of another key sleep-regulating hormone, melatoninWe know melatonin is key to sleep-wake regulation, and without adequate supplies of it, we can expect to experience disrupted sleep. What's worse, broken sleep has consequences that make it more likely for someone to develop depression.  

Appetite changes

These same circadian rhythm shifts also control our hunger drives. Along with a craving for sleep comes a craving to eat more, and usually those cravings include carbohydrates, comfort foods, and sweets... all which can lead to weight gain and can significantly inspire long periods of inactivity and oversleeping. 

'Tis the season

Drops in hormones and increases in appetite are problematic for people who have either depression or SAD. What distinguishes SAD from garden-variety depression, then?


Timing. A typical SAD sufferer experiences shifts in sleeping patterns as early as September and may continue to struggle with their blues through April.

Some sleep specialists identify SAD in this way: if their patient has this kind of a repetitive behavior pattern over three consecutive winters, then SAD is the likely diagnosis. 

Meanwhile, those with depression or other mood disorders that lead to shifts in sleeping patterns tend to experience their symptoms year-round or in a nonseasonal fashion. 

How to treat Seasonal Affective Disorder

The good news: once SAD identified and diagnosed, it is treatable and even preventable. Treatments can be simple, inexpensive, creative, and easily personalized. If you have SAD, you should definitely consult with your sleep specialist about all of the possible therapies you can try for relief.


How to get the help you need

Your best first step is to consult your healthcare provider or sleep specialist about potential sleep and mood disorders. They can help you diagnose your problem correctly and then refer you to the healthcare professional best suited to treat your problem so that you can get your mood—and your sleep—back on track.


American Psychiatric Association 
Mayo Clinic 
National Sleep Foundation
Seasonal Affective Disorder Association

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