Seasonal Affective Disorder: What to Know

The clock strikes five, you collect your things and you leave the office. The thrills and festivities of Christmas and New Year’s are over, the kids are back to school. You’re greeted outside by a cold breeze, snowy roads, and a dark, vanishing sunset. You catch a glimpse of the orange-red sun as it falls behind the hills, blanketed by ash-gray clouds, leaving for tomorrow while you have to stay for today.

By the time you get home, it’s completely dark out; dinner still needs to be made, the dog needs to go out, and you need to hit the gym later. But your mind is telling you to snuggle up on the couch and put on the TV, to ignore all your responsibilities, and to sleep until tomorrow. But you got your full 8 hours of sleep last night, and you had a productive day at work, why the gloom?

The answer could be Seasonal Affective Disorder, aptly put: SAD. SAD affects 6% of Americans, and the “winter blues” affects 14% of Americans, according to one study. The “winter blues” are a more mild variation of SAD, with similar symptoms that are more moderate and intermittent. Let’s dig into the details.

What Causes SAD?

The causes of SAD are wide-ranging and still being studied, but scientists have been studying the disorder since the 1980s. Norman E. Rosenthal M.D., pioneered the work with the National Institute of Mental Health (NIMH) when he moved to the United States from South Africa and noticed a drop in energy and productivity during the winter months of December, January, and February.

Having SAD is defined by the American Psychiatric Association as consistently having depression during certain months or seasons of the year for at least two years, while not having depression during off months, as well as having more time periods of depression than without.

Having SAD during the wintertime is the most common; shorter days and colder weather affect the brain in ways that can lead to depression symptoms. Less sunlight leads to an increase in the production of certain serotonin transporter proteins, SERT. This increase disrupts the transport of serotonin to certain parts of the brain, which can then lead to changes in mood. Serotonin is a complex and essential chemical in your body, and its function in. your brain is to regulate mood, anxiety, and happiness levels.

Another factor the change in sunlight has on the body is melatonin levels. The decrease in sunlight increases the production of melatonin, a hormone that is essential to the body’s control of how sleepy you feel. The more melatonin that is produced, the more tired you feel; melatonin is also an OTC drug used to help people who are having trouble sleeping. Periods of darkness cause the brain to produce melatonin.

Known as the “sunshine vitamin,” vitamin D is primarily produced when UV radiation from the sun interacts with your skin cells to produce cholesterol, which produces vitamin D.Correlation between vitamin D insufficiencies and depression symptoms has been shown in several studies. Vitamin D is also essential in other functions of the brain that regulate mood, as well as bone development. Vitamin D can also be found in fish, meat, and dairy products, as well as vitamin supplements, but most of your vitamin D is going to come from exposure to the sun.

Most of us spend less time under the sun during the winter because it’s just too cold, so it’s not uncommon to have a vitamin D deficiency during the winter; in fact, a 2004 study showed that 41.6% of U.S. adults have a vitamin D deficiency! Those with darker skin are more susceptible because the melanin in their skin does not absorb as much UV radiation.

These changes in serotonin, melatonin, and Vitamin D levels combined can lead to changes in our body’s natural 24-hour rhythm or circadian rhythm. Our circadian rhythm depends heavily on the amount of light we receive from the sun, as well as from the factors above. Our body’s circadian rhythm adapts to the changing of the season, however people who experience SAD or the “winter blues” are thought to have irregular circadian rhythms that are out-of-sync with the seasons, which can lead to a host of depression symptoms.

What are the symptoms?

So what exactly are the symptoms of SAD?  The symptoms have a wide range, but most commonly include: sadness, irritability, lethargy, tiredness, over-sleeping, decreased energy levels, and cravings for fatty and sugary foods. They’re the kind of symptoms you’d pretty much expect. Weight gain is often a  byproduct of these symptoms.

SAD, like many other disorders, comes on a spectrum. For some, a more mild form called subsyndromal S-SAD, or the “winter blues,” occurs. The symptoms are the same, but more mild and less frequent. For others, the syndrome can be as severe as non-seasonal depression, and can even leave one incapacitated for days.

Who’s most likely to get SAD?

SAD does not affect the population of the world uniformly. Those further from the equator are much more likely to experience it: for example, one study found that 9% of Alaskans were affected by SAD, while only 1% of Floridians were. Additionally, women are much more likely to develop SAD, with a 3:1 ratio between women and men. Furthermore, the same study found that in areas of high latitude (Norway and Iceland) some 60% of the population could be undiagnosed for SAD, or S-SAD. Professionals who work night shifts can be more prone to SAD as well, due to the lack of sunlight.

How do I counter SAD?

Treatments for SAD usually include treatment for non-seasonal depression, like antidepressant medications and counseling. Additionally, vitamin D supplements and light therapy can help regulate your brain’s mood-controlling chemicals: serotonin, melatonin, and vitamin D. Combined, these treatment approaches have been shown to be very effective.

Light therapy is typically delivered in the morning, with 5000 lux-hours a day usually given. 1 lux = 1 lumen per meter squared, and as the distance from light source increases, lux decreases by a square factor. So increasing the distance away from a light source 3 times will result in you receiving 1/9 the lux. While an overcast day produces around 1,000-2,000 lux, while a bright, sunny day can produce more than 10,000 lux. So a dosage of 5000  lux-hours is roughly equivalent to sitting outside on a very bright day for 30 minutes.

Light therapy can be received from a lightbox, special desk lamps, light visors, and even light-emitting alarm clocks.

OK, I feel like I might have SAD. How do find out?

You can take the Seasonal Pattern Assessment Questionnaire (SPAQ), a free questionnaire developed by Rosenthal and colleagues in which you can self-assess yourself for the disorder. Be sure to contact your doctor or another medical professional if the SPAQ indicates that you could be affected, self diagnosis is not sufficient to warrant a complete change in lifestyle.

If you want to learn more about SAD, here’s an excellent article put together by the man who started it all: Norman Rosenthal. Complete with eye-catching infographics, and informative arguments, you’re sure to increase your knowledge on the subject.


Seasonal Affective Disorder (SAD) is a disorder that causes depression symptoms most commonly during the winter seasons. Those living in latitudes farther from the equator, and women, are more likely to be affected. A lack of sunlight causes a vitamin D deficiency, increased melatonin levels, and decreased serotonin transport, which can alter the circadian rhythm of your body and your mood. Remedies include depression medication, counseling, sun therapy, and vitamin D supplements.