What Is… Seasonal Affective Disorder

Characteristics of seasonal affective disorder (depression/bipolar with seasonal features)

In this series, I dig a little deeper into the meaning of psychological terms. This week’s term is seasonal affective disorder.

Seasonal affective disorder (SAD) is a subtype of depression or bipolar with symptoms that occur based on a seasonal pattern. It was first described in 1984 as the result of an American study of mostly bipolar patients.

Typically, depressive symptoms occur during the winter, but other patterns are possible. For example, depressive symptoms may appear in the spring, or anxiety symptoms may show up in the summer.


The potential symptoms of SAD are the same set of symptoms that can occur with other types of depression. However, winter depression tends to be more likely to be associated with atypical depressive symptoms like oversleeping, increased appetite, and weight gain.

People with bipolar disorder who have a seasonal element to their illness may be diagnosed as bipolar I or II with seasonal pattern. Seasonal fluctuations are more common with bipolar II than bipolar I. Spring and summer may trigger the onset of mania or hypomania. Among people who have spring/summer onset of depressive symptoms, they’re more likely to experience typical depressive symptoms like insomnia and decreased appetite.

About 70% of people with depression have a worsening of symptoms during the winter, but to actually get the diagnostic specifier of seasonal features, the symptoms must be absent at other times of the year.


The risk for SAD increases at higher latitudes. Approximately 6% of Americans experience SAD, while around 14% experience seasonal dips in mood that don’t meet the full diagnostic criteria for a depressive episode. One survey found that 20% of Irish people experience SAD.

SAD is about four times more common in females than males. In terms of age, the risk increases with age up until the mid-50’s and then drops off after that.

Potential causes

The exact cause of SAD isn’t clear. There’s some indication that there’s a genetic component, with genes related to circadian rhythm maintenance or retinal sensitivity to light playing a potential role. People who experience SAD appear to have difficulty shifting their circadian rhythm to match the changing light conditions.

Changes in melatonin production by the pineal gland in the brain due to lack of light may play a role. Melatonin is a precursor to serotonin, and serotonin is thought to play a key role in SAD.

Vitamin D deficiency related to lack of light may also play a role, but this hasn’t been determined conclusively.

Some research has shown that almost 1/4 of people with SAD also have a personality disorder. While the disorders and their causes are distinct, it may be that there is a personality component that contributes to risk for SAD.


Light therapy is a commonly recommended strategy for managing seasonal affective disorder. In terms of medication, SSRI antidepressants like fluoxetine are commonly used. Bupropion has been approved for the prevention of depression with seasonal features; treatment is initiated in the fall before depressive symptoms set in, and it’s continued until the spring.

Getting regular exposure to outdoor light (even on cloudy days) and physical activity may also be helpful.

While vitamin D supplementation seems like an obvious choice, research results haven’t supported that.

Light therapy

Light therapy one option that can be effective for treating SAD, although research findings have been mixed. Some studies have shown that it’s approximately equal to SSRIs in effectiveness. There should start to be some positive effects within a few days. If there’s no benefit after two weeks, longer exposure may be needed.

Light boxes emit fluorescent light and come in different intensities, measured in lux. Using a 10,000 lux light box would require half the amount of time as a 5000 lux box to get the same effect. Lights can be cool-white or broad-spectrum. Dawn simulators may be helpful for sleep and circadian rhythm, but for SAD, they’re not as effective as a light box.

The typical recommended time for depression is 30 minutes for a 10,000 lux light box. For bipolar, a shorter amount of time may be better. You should sit 30-60 cm (about 1-2 feet) away from the box, at an angle that allows the light to shine in your eyes without staring directly at it. Getting the light in your eyes is more important than getting it on your skin, which is the opposite of how light boosts vitamin D production. Treatments should be done soon after waking up in the morning.

Getting personal

I live on the wet west coast of Canada, just north of the 49th parallel. The biggest issue in the winter here is that it rains a ton, so the sun doesn’t make an appearance very often. While I find cloudy vs sunny days make a transient difference in my mood, winter doesn’t seem to affect my symptom patterns overall. However, since early on in the course of my illness I’ve had a consistent seasonal pattern of a major drop in mood starting in late August and lasting through September. Regardless, I wouldn’t fit the seasonal features specifier, since my illness shows up at all times of the year.

I have a light box that I sometimes use in the winter, but I don’t notice much of an effect from it. I actually prefer the warm glow of my Himalayan salt lamp; it’s not the right kind of light to have the benefits of a light box, but I find it soothing, which is not the case with my cool-white SAD light.

Has seasonal affective disorder been an issue for you? If you have depression or bipolar disorder, do you notice any typical seasonal variations in your symptoms?


You can find the rest of the what is… series in the Psychology Corner.

book cover: Managing the Depression Puzzle, 2nd Edition, by Ashley L. Peterson

Managing the Depression Puzzle takes a holistic look at the different potential pieces that might fit into your unique depression puzzle.

It’s available on Amazon and Google Play.

Ashley L. Peterson headshot

Ashley L. Peterson


Ashley is a former mental health nurse and pharmacist and the author of four books.

35 thoughts on “What Is… Seasonal Affective Disorder”

  1. Love winter now that Ive learned to hibernate! Ive disregarded the modern understanding of time and have learned to shift my activity according to a wheel in the sky. 🥰

  2. Not surprisingly I am of the rare percentage affected in the Spring. My depression cycle worsens from March through April. It begins lessening around mid-May. April has historically been a rough month as far back as high school. The beautiful weather adds a layer of despair I can’t explain. I am Bipolar 1, rapid cycling.

      1. Isn’t it though? I agree. My SAD was noticeable before the other symptoms of depression were. Unable to peel myself from the bed while the weather is perfect impacts me more.

    1. Omg… that’s what I experienced for years. It felt like everyone felt crappy in winter, and then it gets warm and all of a sudden everyone is happy again except for you. I know exactly what you mean about the weather adding a layer of despair. April is bad for me too.

  3. Yay for the mention of Ireland! I’ve known a couple of people who experience SAD but for me personally I don’t think it impacts me. Though I have experienced a worsening of my depression at this time of the year both this year and last year. Something to think about 😊

  4. I did not know it was so prevalent in ireland! The winter months are always harder for me my depressions always worse during those months, but I am not diagnosed with SAd!

    1. I was just taking a look at a study on SAD among blind people, and apparently fully blind people have a higher risk of SAD than fully sighted people, and blind people who are able to detect light have an even higher risk.

  5. Has seasonal affective disorder been an issue for you? Yes. But like you, I have chronic severe depression year ’round, so I’m not sure how accurate the label is. My mood does get worse starting in Sept and going til March though.

    If you have depression or bipolar disorder, do you notice any typical seasonal variations in your symptoms?
    Yep. I’m more melancholy, I seek comfort eating and foods a lot more, and sleep is my good and great friend. Just not healthy sleep O_o My insomnia might ramp up a bit too.

  6. My sunny region of the world, doesn’t have SAD, as we don’t have winter, but monsoons. Monsoons still doesn’t deprive us of sunlight to the extent of seasonal affective disorder.

    But I tend to get depressed in November onwards till around March, same a bunch of other people because it’s a long festive season.

  7. Over here in the UK we start getting a lot of overcast and grey days… and I know I’m going to suffer this year… I’m already feeling the effects…I have a light that hubby got me that is like a bright type of light that can help a little.
    But I do tend to hibernate and if friends do ask to do something, I wanna just stay home…

  8. Yes, and the cold weather alone too…
    I try to force myself to go out for walks with hubby but even that is tough… lately I’ve been going out at dusk… its quite nice actually… and with my acne on my face being so bad (due to B12 injections), and me just feeling ugly anyway, at that time of night at least nobody can see me. But we do wear our reflective jackets, so that we are seen, I’m just saying they can’t see my horrible face…

      1. You are so kind. I do love you Ashley ❤

        Right now I’m feeling extra pants… and premenstrual and I feel like everything is wrong…but that’s how it gets some days…

        I just sit in bed and cry… and last year I had therapy to get me through. This year… … … … …

  9. When I was younger I used to experience mini-breaks twice a year. In the fall and in the spring. Now I have no such pattern to my moods or my anxiety. Not sure whether the 6 month marker was when I was cycling or if there was a weather component to it. Moving from cold, dark climates to sunny Southern climates made a positive impact on my health. I think I am affected somewhat by SAD but never prescribed. Longer days with more light are generally more filled with warm thoughts and feelings than short, cold days with lots of dark.

  10. I find my episodes of depression tend to start around October, November time, but they can persist through summer. My mood seemed a lot better for the last six months or so, but has suddenly gone down a lot in the last week, which I’m trying to monitor, although there’s not much I can do about it other than start using my light box, which is not always easy for practical reasons.

    I didn’t know SAD can be part of bipolar disorder, although it makes sense that it could.

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