Seasonal affective disorder: more than the winter blues

Something shifts in October. The light changes quality — it goes from warm and expansive to thin, arriving late and leaving early. The temperature drops. The days compress. And for a lot of people, something internal shifts along with it: energy dips, motivation drags, mornings get harder, and the general pleasure of daily life starts to feel muted in a way that's hard to explain.

Most people chalk it up to the season. Winter is dark and cold and long, especially in mid and northern Ontario, and feeling less than your best from November to March seems almost logical. So they wait it out.

But for somewhere between 2% and 5% of Canadians, what's happening isn't just a mood dip that comes with the cold. It's Seasonal Affective Disorder — a clinically significant form of depression with a predictable seasonal pattern, a well-understood biological mechanism, and a set of treatments that actually work. A further 10 to 15% experience a milder version that still meaningfully affects their quality of life.

The problem is that SAD is easy to dismiss. Because it has a built-in explanation — it's just winter — and because it eventually resolves on its own in spring, it gets endured rather than treated. And that distinction matters. You don't have to wait it out for 5+ months.

What SAD actually is

Seasonal Affective Disorder is classified clinically as major depressive disorder with a seasonal pattern. It isn't a separate condition from depression — it's depression that follows a predictable seasonal cycle, typically beginning in fall, deepening through winter, and lifting in spring.

What makes it distinct from ordinary winter tiredness is the combination of consistency (it happens most years, not just occasionally), severity (it meaningfully impairs functioning), and the full symptom profile of depression rather than just low energy or mild grumpiness.

Those symptoms include persistent low mood that doesn't lift with good news or circumstances, loss of interest in things that normally matter to you, fatigue that sleep doesn't fix, difficulty concentrating, increased appetite particularly for carbohydrates, sleeping more than usual and still feeling unrefreshed, social withdrawal, and a pervasive sense of heaviness or hopelessness about the months ahead.

It also tends to follow a different profile from non-seasonal depression in some important ways: where classic depression often disrupts sleep (insomnia is a hallmark), winter SAD tends to produce hypersomnia — sleeping too much rather than too little (this can also be present in other/classic depression, but it's got a stronger pattern in SAD). And the appetite changes tend toward craving and weight gain rather than loss of appetite, which can add a layer of shame that discourages people from seeking help.

Why SAD is more common in Canada than almost anywhere

Canada ranks among the highest-latitude countries in the world for winter SAD prevalence — and that's not coincidence. In many Ontario communities, winter daylight hours shrink to fewer than nine hours per day, and the quality of that light is significantly reduced compared to summer. Ottawa, for example, with its northern position and long winters, sits well into the affected range.

The mechanism is largely understood at this point, even if some of its finer details are still being studied.

Light enters the eye and triggers signals that set the brain's master clock — the circadian rhythm that regulates sleep, mood, energy, and hormone production. When light input drops significantly through winter, this clock can drift out of alignment with your actual daily schedule. The result is something like chronic low-grade jet lag: your body's internal timing is off, and your sleep, energy, and mood all reflect that.

Two key neurochemicals are also affected. Serotonin — the neurotransmitter most directly linked to mood regulation — drops in lower-light conditions. Research shows that people with SAD have abnormal regulation of serotonin transport in winter, meaning less of it is available to the brain regions that govern mood, motivation, and emotional regulation. At the same time, melatonin — the hormone that signals darkness to the body and promotes sleep — tends to be produced for longer durations in people with SAD during winter months. More melatonin means more fatigue, more sleepiness, and a body that is chemically being told it's night even when you need to be alert and functioning.

Women are diagnosed with SAD more often than men. It tends to first appear in young adulthood — the twenties and thirties — and while it can affect anyone, having a family history of depression or SAD meaningfully increases the likelihood.

A modern layer: why SAD may be getting worse

SAD isn't new, but there's reason to think the conditions that amplify it are increasingly part of everyday life.

The average Canadian now spends roughly 90% of their time indoors — a figure that has crept upward with the rise of remote work, screen-based leisure, and sedentary routines. This matters because indoor light environments, even well-lit ones, deliver a fraction of the light input your circadian system is built to expect. A bright office typically registers somewhere between 100 and 500 lux. An overcast October day outside registers closer to 10,000 lux — the same intensity used in clinical light therapy. The gap between what we're getting and what our biology needs is significant, and most people aren't aware of it.

Screens add a separate layer at the other end of the day. Evening exposure to the blue-spectrum light emitted by phones, laptops, and televisions suppresses melatonin production at exactly the time the body needs it to rise in preparation for sleep. The result is delayed sleep onset, reduced sleep quality, and a circadian rhythm that is being pushed in conflicting directions — too little stimulating light during the day, disruptive light at night. For people already vulnerable to SAD, this pattern compounds the neurochemical disruption that winter sets in motion.

None of this means screens cause SAD. But it does mean that many people are living in light environments that amplify seasonal vulnerability rather than buffer against it — and that some of the most effective things you can do for winter mood don't require a prescription, just a deliberate shift in when and where you're exposed to light.

The difference between SAD and the winter blues

This is worth being clear about, because conflating them leads people to either under-treat SAD or over-pathologize the entirely normal experience of feeling less energetic in winter.

The winter blues — sometimes called subsyndromal SAD — are real, common, and meaningful. They involve lower energy, less motivation, some mood dip, and a general preference for staying in with tea rather than doing anything ambitious. They're responsive to lifestyle adjustments, extra time outdoors on bright days, staying socially connected, and moving your body. They tend not to significantly impair your ability to work, maintain relationships, or experience pleasure.

SAD is more than this. The mood change is persistent and pervasive. Functioning is genuinely impaired — work suffers, relationships suffer, basic self-care can feel like too much. There's often a quality of hopelessness that isn't proportionate to circumstances. And critically, it doesn't respond reliably to the things that help the winter blues. You can take all the right self-care steps and still be struggling.

The informal test that often helps: if your symptoms are significantly interfering with your daily life, and they've followed this pattern for at least two consecutive years, SAD is worth taking seriously rather than waiting out.

What actually works

This is where the news is genuinely good. SAD responds well to treatment — usually quite quickly — and there are several effective options that can be combined depending on what someone needs.

Light therapy is typically the first line of treatment, and for good reason. A randomized controlled trial conducted across four Canadian centres found light therapy to be as effective as antidepressant medication for SAD, with the advantage of faster response and fewer side effects. The protocol is

straightforward: 20 to 30 minutes each morning in front of a lightbox that produces 10,000 lux of bright white light, starting within the first hour of waking. Most people begin noticing improvement within one to two weeks. Lightboxes are readily available, starting at roughly $50 to $80 for a basic model. If you are taking photosensitizing medications, it's worth checking with a doctor first.

Psychotherapy — particularly CBT adapted for SAD — has strong evidence behind it, and meaningfully outperforms light therapy on one important metric: recurrence. Research has found that people who completed CBT for SAD had lower rates of depression the following winter compared to those who used light therapy alone. This makes sense: light therapy addresses the neurochemical mechanism, while therapy addresses the patterns of thinking and behaviour that develop around it — the withdrawal, the hopelessness, the hibernation that deepens the depression rather than protecting against it.

Medication — typically SSRIs — is effective and appropriate for some people, particularly when SAD is severe or when other approaches haven't provided sufficient relief. This is a conversation worth having with a family doctor.

Lifestyle factors have genuine but more modest effects. Getting outside during daylight hours — even on overcast days, which still provide significantly more light than indoor environments — helps. Regular movement, maintaining social connection rather than withdrawing, moderating alcohol (which depresses mood and disrupts sleep), and keeping sleep timing consistent rather than oversleeping on weekends all support the other treatments. These things won't treat clinical SAD on their own, but they're meaningful adjuncts.

Why people wait too long

The most common reason people don't seek support for SAD is the same reason it's underdiagnosed in general: the seasonal pattern is its own explanation. Of course I feel worse in winter. Everyone finds January hard. It'll pass when the days get longer.

All of that may be true and still miss the point. Five months is a long time to feel like a diminished version of yourself. Five months of reduced functioning, lower mood, more conflict in your relationships, less engagement with your life adds up to something significant — and it's happening every year, not just this year.

You don't need to reach a threshold of suffering before help is warranted. If the pattern is clear and it's affecting your life, that's enough.

Starting now rather than waiting for spring

If what you're reading here resonates — if some version of this pattern has been showing up for you over the past few winters and you've been managing it rather than actually addressing it — October is the right time to act, not January.

Light therapy works best when started at or before the onset of symptoms, before the depression has a chance to fully establish. Therapy takes time to build momentum. And establishing support while you're still functional is considerably easier than trying to reach out when you're deep in the lowest months.

If you're in Ontario and you'd like to explore what's going on, I offer a free 15-minute consultation call. We can talk about what the pattern looks like for you, what might help, and whether working together makes sense.

Gwen Preston is a Registered Psychotherapist offering virtual therapy across Ontario and in-person sessions in Orleans. She works with adults and teens on depression, anxiety, burnout, and seasonal mental health, using ACT, CBT, and MBCT adapted to each client's specific situation. Free 15-minute consultations are available through the booking page.