For me, fall is my favorite time of the year.
The frantic randomness of spring and the empty void of summer are behind us, with the cooling weather settling us all into this groove of productivity and relaxation. As the school year phases in, I’m able to get into the zone and work on projects that were previously only thoughts.
The colder weather outside also means I get to stay inside, snuggled with a blanket, a cup of hot chocolate and a horror classic to honor the approaching Halloween.
For some, however, fall doesn’t mean relaxation and productivity, it means losing motivation and even experiencing depressive symptoms.
This is thanks to seasonal depression, known officially as seasonal affective disorder, or SAD. SAD is a mental disorder where certain people experience depressive symptoms during certain parts of the year.
According to the Cleveland Clinic, there are half a million cases of SAD in the United States every year, and millions more around the globe. The condition usually begins during the onset of fall, worsening as fall progresses into winter, and then it begins to alleviate during spring.
The condition was officially defined in the 1980’s, however it’s been recorded many times before that. French physician Philippe Pinel recorded mental deterioration in his psychiatric patients during the winter in his “Treatise on Insanity”, which was written in 1806. Much earlier, in roughly 300 BC, the treatise “The Yellow Emperor’s Classic of Medicine” recorded the more general concept of the “winter blues” and how winter is a time of conservation and limited activity.
Symptoms of SAD are fairly similar to those of clinical depression. They include oversleeping, appetite changes, weight gain, fatigue, difficulty concentrating, feelings of hopelessness, and frequent thoughts about suicide, among others.
The condition is more common in women, with three-quarters of all SAD sufferers being women, and SAD is most common in young adults, seeming to wane by older adulthood.
While SAD is a condition on its own, it’s also known that seasonal changes can worsen existing mental conditions. 15% of depression patients and 19% of bipolar disorder patients have noted more severe symptoms in certain seasons, and with bipolar patients specifically, summer is known to bring on mania.
SAD varies a lot geographically, and the further you get from the equator, the worse the condition gets. SAD is at its worst above 30°N latitude — which is the latitude of Cairo and Houston, Texas — and below 30°S latitude — which is around Lesotho and the San Juan Province in Argentina.
Now that we know some background about SAD, we have to ask, why does it happen?
Scientists don’t know for certain what causes SAD, but there are a variety of explanations for it. The general agreement is that SAD has to do with there being less light in the winter due to shorter days, and the most common explanation is that lower light disrupts circadian rhythms.
Your circadian rhythm is a 24-hour cycle that regulates when you feel tired, and it controls a lot of things in your body. The circadian rhythm is regulated by light cycles, which is why low light in winter could disrupt it.
In your eyes, you have these cells called intrinsically photosensitive retinal ganglion cells, abbreviated to ipRGCs. These are cells that detect light you’re seeing and send signals about the light levels in your brain.
ipRGCs are how your brain detects light, and they work even if you can’t see.
The ipRGCs, when they detect light, send signals to a part of your brain called the suprachiasmatic nucleus, or SCN, and that regulates your circadian rhythm. The ipRGCs report how much they’re being stimulated, and they get more stimulated the more light there is.
Based on how much the ipRGCs are being stimulated, the SCN can determine how light it is outside, and it sends that signal to your pineal gland.
The pineal gland is a gland in your brain that controls the secretion of a brain chemical called melatonin. Melatonin is a chemical that regulates mood and sleep, and the more melatonin there is in your body, the more tired you feel.
So, in accordance with the light, your brain determines how much melatonin to produce, which determines your sleep pattern. When it’s light out, and your ipRGCs are being stimulated, you’ll feel awake and alert as not much melatonin will get produced. When it’s dark out, however, you’ll start to feel tired, as your ipRGCs aren’t being stimulated, so you’re brain produces more melatonin.
This all goes to explain SAD.
In the winter, there is lower light thanks to shorter days. Due to this, your brain begins to produce more melatonin as it believes it’s dark out and you should feel tired. This leads to you having more melatonin than you should, meaning you’re tired a lot more often, and that can spiral into other problems and eventually depression.
Always being tired will make it harder to concentrate, make you feel hopeless as everything is a chore to complete, and it could lead to problems with eating. These life problems could double on themselves, exacerbating your depression and possibly causing suicidal thoughts.
This explanation does line up with what we already know about melatonin and depression. A study by the American Journal of Psychiatry found that when patients with clinical depression were administered doses of melatonin, their symptoms worsened, which supports the idea that melatonin causes depression, and it explains why already depressed people could have their symptoms worsen in the winter.
SAD doesn’t just involve melatonin, however. There are other brain processes at work that could cause a change in season to create depression.
There are these genes called clock genes, which are responsible for transcribing the circadian rhythm. They’re essentially the messengers of your sleep schedule, communicating throughout the body when you should feel awake or tired, and they do part of this by controlling monoamine transmission.
Monoamines are a broad category of brain chemicals that include serotonin and dopamine, which are responsible for regulation of mood and appetite, among other things.
Monoamines have been shown to be regulated by the circadian rhythm, and have reflected it in terms of their behavior. Studies have found that disruptions in the circadian rhythm have also lead to disruptions in the production of monoamines.
This means that during a period of low light in winter, not only would there be excess melatonin, but disrupted clock genes could also be inhibiting the production of other vital brain chemicals like serotonin and dopamine, which could spiral into depression.
There’s also a protein called 5-HTT that could play a part in SAD. Studies have found that people with SAD have, on average, 5% more of the 5-HTT protein than the average person. This is problematic because 5-HTT stops serotonin from crossing synapses, and instead sends it back to the presynaptic neuron to be reused.
Basically, it keeps serotonin from working, and in moderate amounts, this is good as it regulates serotonin in the brain and keeps there from being too much. However, with SAD, there can be too many of these proteins and serotonin levels can be too low, causing mood problems.
The connection between 5-HTT and SAD isn’t exactly known, nor is it known how light levels impact amounts of 5-HTT in the brain, however it is likely that it plays some role in decreasing the serotonin levels in SAD patients.
Now, knowing this, we have to wonder why some people get SAD and others don’t. After all, we all experience low light in the winter, so why doesn’t everyone get depressed as a result?
In this case, it likely has to do with the sensitivity of the clock genes and the SCN. In some people, these are simply more sensitive to changes in light, meaning they’re more likely to dip into a depression if light levels get low. With most of us, however, we’re not sensitive enough, so our circadian rhythms remain intact.
So, for most of us, we’re okay during the winter, but the millions of people worldwide suffer from SAD, and it can be a real problem. SAD can significantly disrupt life, especially during a time that’s supposed to be festive, and to deal with it, many treatments have been created.
The first is light therapy. Light therapy has become the leading treatment for SAD since the 1980’s, and it makes sense, as it directly addresses the cause: low light. With light therapy, a SAD patient sits in front of a light box for 20–60 minutes a day, with the box shining up to 20 times the typical light level indoors.
This can work to compensate for lower light in the winter, and keep the brain in a healthy cycle, which will stop the onset of SAD.
Another common treatment for SAD is medication. There are two major medications that are prescribed to help treat SAD: selective serotonin reuptake inhibitors (SSRIs) and Bupropion.
SSRIs are used to raise serotonin levels in SAD patients by combating the 5-HTT protein. SSRIs prevent the formation of 5-HTT, and therefore the recycling of serotonin, meaning it’s easier for serotonin to move throughout the brain and perform its function. This helps maintain a healthy level of serotonin in SAD patients, and can decrease the severity of depressive symptoms.
Bupropion performs a similar function to SSRIs. It prevents the reuptake of serotonin, but it also helps the production of other feel-good chemicals like dopamine and norepinephrine. Generally, bupropion is meant to raise the levels of these chemicals in the brain, and alleviate depressive symptoms.
The final treatment for SAD is therapy.
The most common therapy when it comes to SAD is positive thought therapy. Therapists help SAD patients replace their negative thoughts with positive ones, and encourage them to think of pleasurable activities they can do inside to cope with the winter weather.
This is fairly traditional for treating mental disorders, and studies have found that with SAD specifically, this behavioral/thought-based therapy is just as effective as light therapy.
Alongside these treatments, some countries with harsh winters have learned to cherish and value the cold, and the cultural appreciation of the season has been a way that the entire community combats SAD.
In an interview with The Atlantic, Ane-Marie Hektoen gave an account of her experience moving to one of the northernmost cities in the world, Tromsø, Norway.
Tromsø is nearly 250 miles, or 400 kilometers, north of the Arctic Circle, and in the winter the sun doesn’t rise from November 21st to January 21st. If there was a community with a dark winter, where it would be justified for residents to begin feeling depressed due to the weather, it was here.
Coming from southern Norway, Hektoen said her perception of winter was that it was a season she had to plow through and survive, but in Tromsø, the attitude was a lot different. Despite it being super dreary and harsh, the locals in Tromsø saw the winter as a cozy time — they learned to appreciate the darkness, the snow, and the comfort of being able to escape the cold and huddle around a fire inside.
The attitude of the community towards the winter was a lot more positive, which made people less likely to get down just because it was dark outside.
Similarly, psychologist Kari Leibowitz did a survey throughout Scandinavia and found that the further north she went, the more positive people’s attitudes were towards the winter. This indicates that there is a sort of cultural adaptation to the harsh winters there that’s used to combat SAD.
Overall, SAD is an incredibly intriguing disorder. Although there are many theories about it, how it works is still mysterious to us, and its impact on the world is unmistakable. It has left a unique footprint on human history and culture, and many countries have found fascinating ways of coping with their harsh winters and preventing the cold weather from getting them down.