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Seasonal Affective Disorder

Updated: Jul 29, 2023

What is Seasonal Affective Disorder?

Seasonal affective disorder (SAD) is a severe version of “winter blues”, aka depression that coincides with changing seasons, mostly as we enter winter until spring (1). SAD is more common in countries with fewer daylight hours in the winter, including the country currently known as Canada. SAD is also more common in people with a family history of SAD or depression, people assigned female at birth, and young adults (aged 18-30 years old) (2). Previous studies have shown that skin pigmentation may play a role in SAD susceptibility as well (3). Darker skin tones have increased levels of melanin, which may contribute to changes in levels of vitamin D, which may play a role in SAD (more on this below). Further research is needed to clarify the relationship between skin pigmentation and SAD.

SAD symptoms are similar to clinical depression and include low mood most of the day and nearly everyday, losing interest in activities, feeling sluggish or agitated, changes in sleep, difficulty concentrating, feelings of hopelessness, worthlessness or guilt. Commonly, some people experience changes in appetite, including overeating and increased craving for carbohydrates (white bread here I come!) (4).

Diagnosis of SAD also means these depression symptoms go away in the summer months (2). If the symptoms do not follow a seasonal pattern, this may be more consistent with another type of depression disorder, such as Major Depressive Disorder. Less frequently, some people may experience SAD during the summer months and experience different symptoms, including insomnia, poor appetite, weight loss, agitation and anxiety (5). Research shows that summer-related SAD is more prevalent in tropical climates closer to the equator (6).

Biology of SAD:

There are many different ideas and theories about why some people experience SAD. The leading idea is … SAD is complicated. Various scientists have looked at where people live, exposure to sunshine and vitamin D metabolism, as well as differences in sleep cycles. In reality, we do not have a clear-cut answer but it is likely that SAD is due to a combination of biological and social conditions.

“I’m SAD.” Hi SAD, I’m Hormones!

Before we get into the biology of SAD, it’s important to understand the basics of some important hormones in our body.

Serotonin is a neurotransmitter that is produced in the brain and in the gut. Colloquially, serotonin is known as the “happiness” brain chemical, but it actually has complex and intersecting roles in mood, appetite, memory, sexuality, and so many more systems (11). Serotonin is targeted in psychiatric disorders, including Major Depressive Disorder, with some antidepressant drugs like Selective Serotonin Reuptake Inhibitors (SSRIs; e.g. Prozac).

Dopamine is made mainly by the brain and is commonly referred to as the “pleasure” brain chemical. Dopamine reinforces habits that provide “pleasure”, thereby influencing motivation, and is indicated as an important chemical in depression, attention-deficit hyperactivity disorder (ADHD) and addiction neuroscience. Disturbances in dopamine may contribute to low mood and lack of interest in activities seen in SAD (3).

Melatonin is a hormone produced by the pineal gland and functions as a way to sync our bodies with our environment, especially in regards to the day-night cycle. Darkness stimulates the production of melatonin, whereas light inhibits melatonin (12). Melatonin is like our body’s sleepy-time tea! In the context of depression and SAD, there is mixed evidence for melatonin as a therapeutic or harmful supplement.

Are we just complicated plants?

Like plants, we love sunlight. But why is sunlight important, especially in the context of SAD? People who live in higher latitudes, further away from the equator, have less exposure to sunlight throughout the year. In these areas, there is also a higher prevalence of SAD (7). Sunlight is important in the activation of vitamin D, which in turn influences a wide range of critical biological processes.

The ability to absorb sunlight can impact vitamin D activation. For people with darker skin tones, the increased melanin in the skin acts as a shield from harsh ultraviolet light (you still need sunscreen though!). However, this can also reduce the absorption of the light and vitamin D activation. Previous research shows African-American women have a tenfold higher prevalence of hypovitaminosis D (lower than average vitamin D levels) (8). Lower overall levels of vitamin D could help explain the association between skin pigmentation and SAD (3).

Vitamin D deficiency is common in Canada. Approximately a third of Canadians have Vitamin D deficiency. This is especially pronounced in Canadians aged 20-29 years old, in which 41% have insufficient Vitamin D levels (9). Historically, people who live far from the equator and therefore see less sunlight compensate by eating vitamin D rich foods (e.g. oily fish like salmon or mackerel) (10). However, now vitamin D supplementation is available in various forms, such as daily pills. A blood test is required to measure vitamin D levels. However, the cost associated with a vitamin D test is not generally covered by the Ontario Health Insurance Plan (OHIP).* Through LifeLabs, the test costs $80 per person. Talk to your healthcare provider to learn more about vitamin D testing and supplementation.

Oh no… my internal clock… it’s broken…

Decreased sunlight can also impair our internal clocks, also known as our circadian rhythm, which controls our body’s timing. For example, the circadian rhythm controls hormones that tell us when we get hungry, when we feel sleepy and what time we wake up in the morning. With decreased light, like in the winter, different systems can feel “out-of-whack”, which can be magnified in SAD. A significant hormone that is impacted in SAD and in the winter months is melatonin. Altered melatonin can lead to altered sleep patterns, sluggishness, and low energy - all symptoms of SAD. An antidepressant called agomelatine activates melatonin receptors which leads to greater melatonin production in the body, and may reduce symptoms of SAD. Another theory is that SAD is caused by the alteration of brain chemicals, including serotonin and dopamine, in response to decreased light and vitamin D in the winters.

Beyond the Biology:

SAD is a complex mood disorder that is still a mystery to many scientists. Beyond the science, other factors to consider with SAD susceptibility include different life circumstances that make winter especially dreary for some. Winter months may place more pressure on people with complex or difficult family situations with winter holidays, increased spending, grief, reduced ability to exercise, get outside or enjoy activities. Other mental health concerns, like anxiety, may also contribute to winter blues. These factors are specific to a person’s situation, identity and coping mechanisms. More research exploring the impact of social situations on SAD is needed.

While the science may point to vitamin D supplements or light-therapy, these tools may not be sufficient for people with intersecting challenges.

Treating SAD:

Treating SAD will depend on each person, the severity of their symptoms and their goals. The firstline treatment for SAD (specifically Winter-SAD), as recommended by medical guidelines, is antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs), plus/minus light therapy (discussed below) (13). For long-term SAD, non-SSRI antidepressants like Buprion/Wellbutrin may help (14). For less severe forms of SAD, patients can opt to try light therapy first and add antidepressants if light therapy alone is ineffective. Please consult with your doctor before starting any treatments or interventions so you can find the best plan for you.

What is light therapy?

Light therapy is a relatively new treatment option. Two options recommended are either 1) bright light therapy or 2) dawn stimulation. Briefly, bright light therapy involves staring into a super bright box. Seems simple, right? The bright light hits your eyes, sending a “wake-up” signal to your brain and reducing symptoms of SAD. Commercial light boxes are recommended as home-made boxes may not reach the desired brightness, produce too much heat or be unable to filter out harmful ultraviolet light rays. It is recommended to use bright light therapy in the morning, at the same time everyday, for about 30-60 min per day. Lights with lower brightness would require longer time. The most common negative side effects include eye strain and headache.

Dawn simulation is used in the final hours of sleep to mimic a sunrise in your bedroom. The device functions by emitting a low light that gradually increases in intensity. Some people find it helpful to use both light therapies concurrently.


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