Seasonal affective disorder guide

Seasonal affective disorder (SAD) is a type of bipolar depression that follows a seasonal pattern, typically occurring during the fall and winter months when daylight hours are shorter.

It’s more than just the “winter blues” because it’s a legitimate form of clinical depression with biological, psychological, and environmental factors playing a role.

I created this guide because I noticed that my mood tends to worsen in winter periods when there’s little sunlight here in Belgium.

Crucial characteristics

• Onset
  
  

Usually begins in late fall or early winter.

• Remission

Symptoms tend to ease during spring and summer.

• Type

Considered a subtype of major depressive disorder (MDD) or bipolar disorder (especially Bipolar II).

Common symptoms

The symptoms are similar to major depression but often come with a seasonal pattern:

• Low energy, fatigue, and oversleeping.

• Depressed mood most of the day, nearly every day.

• Loss of interest or pleasure in usual activities.

• Difficulty concentrating.
  

• Feelings of hopelessness or worthlessness.

• Increased appetite (especially for carbs), leading to weight gain.

• Social withdrawal (“hibernating” behavior).

Take note that SAD can occur in spring or summer in rare instances. This is known as reverse SAD, which may involve insomnia, agitation, and weight loss.

I usually feel more tired than usual when fall and winter are around.

What causes it?

The exact cause isn’t fully understood, but research points to a combination of:

• Reduced sunlight exposure → disrupts circadian rhythms.
  

• Melatonin overproduction → leads to increased sleepiness.

• Serotonin imbalance → contributes to mood changes.

• Vitamin D deficiency → may affect serotonin levels and mood.

People in higher latitudes, such as in Europe or Canada, are more prone to SAD due to longer periods of darkness in winter.

Belgium is a rainy country, and we go for longer periods without sunlight. I always detect my thinking becoming more negative and prone to catastrophizing around these times.

Who’s most at risk?

• Women (SAD is about 4x more common in women than men).

• People aged 18–30.

• Individuals with a personal or family history of depression or bipolar disorder.

• People living far from the equator.

Evidence-based treatment options

1. Light therapy (phototherapy)

• • Most effective, especially if it started early in the season.

• • Involves sitting near a 10,000-lux light box for ~20–30 minutes each morning.

• • Shown to improve symptoms in 60–80% of people with SAD.

2. Cognitive behavioral therapy (CBT-SAD)
   
   

• • A modified form of CBT designed for SAD.

• • Aims at discovering pessimistic thoughts about winter and promoting behavioral activation.

• • Studies show it may have longer-lasting effects than light therapy.

3. Medication

• • SSRIs like fluoxetine or bupropion XL are often prescribed.

• • Bupropion is FDA-approved for preventing SAD episodes if started before symptoms begin.

4. Lifestyle support

• • Daily walks, mainly in daylight.

• • Keeping a regular sleep schedule.

• • Balanced diet and regular exercise.

• • Mindfulness or relaxation techniques.

I keep a tight workout schedule since it’s proven to release neurotransmitters that make us feel better.

How common is seasonal affective disorder?

It’s relatively common, specifically in regions with long, dark winters, but its prevalence varies depending on location, population, and diagnostic criteria.

• General population

Around 1–10% of people experience clinical SAD (a diagnosable form of depression with seasonal patterns).

• Subsyndromal SAD (“winter blues”)

A milder form affects 10–20% of people, with symptoms that don’t meet full diagnostic criteria but still impact mood and energy.

• Women

Women are 4 times more likely than men to experience SAD.

• Young adults

Most common in people aged 18–30.

Geography matters a lot

Rates increase with distance from the equator due to decreased sunlight exposure in winter.

• Northern Europe and Canada

Up to 9–10% may experience SAD (e.g., parts of Scandinavia, Alaska, or Newfoundland)

• United States

SAD affects about:

• • 1% in Florida.

• • 9% in Alaska.

• • The national average is around 5%.

• Belgium

While exact national data is limited, studies in similar latitudes (like the Netherlands or Germany) suggest around 3–5% experience SAD, with a higher percentage experiencing milder winter blues.

How is seasonal affective disorder diagnosed?

Diagnosing SAD involves more than just noticing you feel a bit “off” in the winter.

It’s a clinical diagnosis, meaning it follows specific criteria used by mental health professionals, most commonly those in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition).

It isn’t a standalone diagnosis. Not only that, but it’s classified as a specifier for major depressive disorder (MDD) or bipolar disorder, meaning the depression occurs in a seasonal pattern.

To meet the diagnostic criteria, a person must:

1. Meet criteria for a major depressive episode

• • At least 5 symptoms (low mood, fatigue, sleep issues, loss of interest) lasting for 2+ weeks.

• • Symptoms cause noteworthy distress or impairment.

2. Seasonal pattern

• • Depressive episodes occur at the same time of year (usually fall or winter).

• • Full remission or change to mania/hypomania occurs in a specific season (typically spring/summer).

3. Repetition over time

• • This seasonal pattern has happened for at least 2 consecutive years.

• • More seasonal episodes than non-seasonal ones throughout the person’s lifetime.

4. No better explanation

1. • Symptoms aren’t better explained by seasonal stress, such as job loss around the holidays, for instance.

Additional diagnostic tools

While there’s no blood test or scan for SAD, clinicians often use:

• Structured clinical interviews (e.g., MINI, SCID).

• Self-report questionnaires like:

• • SIGH-SAD (Structured Interview Guide for Hamilton Depression Rating Scale – Seasonal Affective Disorder Version).

• • Seasonal Pattern Assessment Questionnaire (SPAQ).

Widely used but less reliable for formal diagnosis.

• Rule-outs for:

• • Thyroid issues (e.g., hypothyroidism).

• • Anemia.

• • Vitamin D deficiency.

• • Other psychiatric disorders like dysthymia and bipolar disorder.

• Differential diagnosis (what SAD might be mistaken for):

• • Major depression (non-seasonal).

• • Bipolar II disorder (particularly if depressive episodes occur in winter and hypomania in summer).

• • Dysthymia (persistent mild depression).

• • Vitamin D or iron deficiency, which can mimic fatigue symptoms.

Why is it often underdiagnosed?

SAD is often underdiagnosed because many people think feeling tired or down in winter is just “normal.”

For example, while I always feel a bit more weary around that time, it’s certainly not as bad as when I was suffering from severe acute depression.

But it’s worth seeking treatment if symptoms interfere with daily life and recur each year.

When do I seek help?

If you (or someone you know) notice recurring low mood, fatigue, or disinterest every fall or winter, and it’s affecting work, relationships, or daily functioning, that’s a signal to talk to a mental health professional.

Early diagnosis = earlier treatment = better outcomes.

Final thoughts

SAD is a serious, periodic form of depression.

It’s treatable, and early intervention (preferably before winter hits) can make a big difference.

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