Winter-Pattern SAD (Winter-Onset Depression)

🧠Overview — What is Winter-Pattern SAD (Winter-Onset Depression)?

Winter-Pattern SAD is one of the most specific and clearly defined forms of mood disorder that “ties a person’s life to the seasons” in a very systematic way in modern psychiatry. It is not just ordinary loneliness, feeling cold, or feeling a bit flat in winter like most people experience, but rather a full depressive episode that occurs in the same season every year in a patterned and predictable way, almost as if there were a scheduled program running in the brain.

The most distinctive feature of Winter-Pattern SAD is that depressive episodes begin in late autumn to early winter, and gradually ease on their own when spring and summer arrive—whether or not treatment has been given. It is as if hormones, light exposure, and the body’s biological clock spontaneously “move back into a normal phase” when the environment changes.

In DSM-5-TR, it is classified as a specifier of a primary mood disorder (such as MDD or Bipolar Disorder), not as a separate disease entity. The core focus is on the pattern of occurrence of depressive episodes, rather than the symptom content itself. The person must already have a primary depressive or mood disorder, but the episodes are clearly tied to a seasonal cycle, such that the depressive episodes come “specifically in winter”.

This pattern must recur for at least 2 consecutive years, and the number of depressive episodes that occur in that particular season must be “significantly greater” than episodes occurring outside that season across the person’s lifetime. This point is crucial because it helps distinguish between “true SAD” and “just happening to be depressed at the end of the year because of overwork” or “recurrent life problems that happen to occur in the same period every year.”

Winter-Pattern SAD is often accompanied by specific symptoms called winter-atypical features, such as sleeping more, craving carbohydrates and sweets, weight gain, social withdrawal, and feeling as if one’s energy is abnormally low. This contrasts with melancholic depression, where people typically eat less and have insomnia. These differences give Winter-SAD a distinctive clinical profile and a more specific neurobiological mechanism.

From a neuroscience perspective, winter is associated with reduced duration of light exposure, leading to circadian misalignment, prolonged melatonin secretion, and changes in the serotonin/dopamine systems that are linked to mood, energy, and motivation. It is therefore not surprising that some individuals are much more sensitive to these changes than others.

Epidemiological studies consistently show that Winter-Pattern SAD is more common in high-latitude countries (where daytime is very short in winter), such as Canada, Norway, and Finland. However, it can still be found in tropical countries, particularly in regions or periods with prolonged cloud cover, continuous rainfall, or lifestyles that keep people indoors nearly all day with very little natural light exposure.

Although it is sometimes casually referred to as “winter blues,” it must be emphasized that Winter-Pattern SAD is a full clinical depression that significantly impacts work, study, and quality of life—for example: being unable to get up for work, forgetfulness, reduced concentration, weight gain leading to self-disgust, or social withdrawal that disrupts teamwork and relationships.

In addition, in some people—especially those with Bipolar Disorder—winter becomes the season of depression, and summer becomes the season of hypomania/mania. This makes it very important to examine symptom history across other seasons as well, because having the wrong treatment plan or direction may risk making mood swings worse.

In summary, Winter-Pattern SAD is a “seasonal mood disorder” with a clearly structured pattern at the levels of symptoms, behavior, brain mechanisms, and temporal course. It is a condition that can be predicted in advance, and for that very reason, prevention, advance planning, and light- and behavior-based management can be highly effective if started before the high-risk season.

Core Symptoms — Core Symptoms of Winter-Pattern SAD

Overall, the symptom profile of Winter-Pattern SAD can be summarized as “a full depressive episode” + “a winter-specific signature.”
Clinically speaking, the person is not just “a bit gloomy when the weather is dark,” but rather their entire life starts to slow down, they fatigue easily, fall out of their routines, and this pattern appears repeatedly only in late-year to early-year periods.

2.1 Mood and Cognitive Cluster

This is the “central core” of depressive episodes of all types, including Winter-Pattern SAD.

Persistently depressed, sad, and bleak mood for many weeks
It is not just “a couple of bad days” and then it’s over, but a sustained sense of dullness and sadness, as if everything is covered by a gray filter all day long. They wake up already feeling heavy, even without any clearly identifiable adverse life events in that period.

Feelings of hopelessness and a bleak view of the future
Patients often say things like, “I can’t see myself getting through this,” or “Next year will just be like this again anyway.” They are not only sad about the present, but their “mental picture of the future” is also tinted with hopelessness.

Reduced interest or pleasure in previously enjoyed activities (anhedonia)
Activities that used to bring enjoyment—gaming, drawing, writing fiction, watching series—no longer feel engaging. During Winter-SAD, they often feel: “I could do it or not do it, it doesn’t really matter; nothing feels fun.” Activities that used to be sources of emotional energy become neutral or something they feel they have to force themselves to do.

Feelings of worthlessness and disappointment in oneself
Even though the primary underlying cause is biological (light and seasonal changes), the “content of thoughts” in their mind often attacks themselves: “Why am I this weak? Other people can handle it,” or “I become a burden to others every winter.” This self-critical narrative intensifies and reinforces the depressive cycle.

Reduced concentration, slowed thinking, and difficulty making decisions
Many people don’t realize they are “depressed” at first; instead, they come to see a doctor because they feel that:
– They can’t work effectively; their mind feels blocked; they can’t absorb what they read.
– They take a long time to decide even simple things, such as how to reply to a message or which task to start with.
All of these are part of cognitive symptoms in depression.

Overall, the mood and cognitive cluster is what makes Winter-Pattern SAD fit clearly within the spectrum of Major Depressive Disorder, not just “disliking winter weather.”

2.2 Motivation, Energy, and Daily Functioning Cluster

This cluster is what people around the patient usually notice first, because it concerns “real-life functioning.”

Easily fatigued, exhausted, feeling “heavy-bodied and heavy-hearted”
This is not fatigue from excessive work, but a sense of carrying something heavy all over the body. Just getting out of bed to shower can feel like it consumes all their energy for the day. Some people describe it as “my body feels as if it’s weighed down with sand” (a leaden feeling), even when they have not done much.

Slowed daily activities; difficulty dragging themselves to work/school
Starting small tasks like turning on the computer, replying to emails, or washing dishes becomes a “major mission” requiring a long period of mental preparation. Many end up procrastinating repeatedly until tasks pile up, which then triggers guilt on top of the depression.

Decreased work or academic performance
– They complete tasks more slowly than usual.
– They forget appointments and deadlines.
– Tasks that used to be easy now take much longer.

This is important because it makes the “impact on real life” very clear, and is one of the reasons Winter-SAD is not just about mood—it clearly includes functional impairment.

The outcome is that many people begin to feel, “I’m no longer competent,” which reinforces feelings of worthlessness → which deepens depression → which makes it even harder to do anything, creating a downward spiral.

2.3 “Winter-Type Atypical Features” Signature

This part is essentially the signature of Winter-Pattern SAD, clearly distinguishable from classic melancholic MDD.

Sleeping excessively (Hypersomnia)
While many people with stress/depression may have insomnia, Winter-SAD tends to “shut the world out by sleeping.”
– They may sleep 10–14 hours per day.
– They wake up still feeling drowsy and heavy-headed, wanting to go back to sleep.
– Some say it feels like “there is no moment in the day when I feel truly refreshed.”
This is on top of daytime napping or spending an entire day off in bed.

Increased craving for carbohydrates and sweets (craving for carbs & sweets)
This is notably different from the typical pattern of decreased appetite/weight loss in melancholic depression.
– Craving rice, bread, noodles, desserts, sugar.
– Often eating in an emotional or mildly binge-like way just to feel better briefly.

Biologically, this is linked to the body’s attempt to increase tryptophan intake to produce more serotonin, but in the long run it leads to weight gain and guilt about one’s eating, which further worsens mood.

Winter weight gain

This results from:

– High carbohydrate/sugar intake

– Reduced physical activity

– Increased sleep

– Some people see their weight go up by 2–5 kg in a single season.

– This worsens body image and lowers self-confidence, further intensifying depression.

Social withdrawal — hiding away in “hibernation mode”

– Not wanting to go out and see people.

– Increasingly canceling plans with excuses like “I’d rather just stay home.”

– Ignoring messages, leaving others on read, or disappearing from chats for weeks.

People around them may misunderstand, thinking they don’t want to maintain relationships or that they have become cold, when in reality the underlying issue is “no energy to handle social interaction.”

Sense of “heaviness in the body and limbs” (leaden paralysis)
This is a symptom that textbooks often highlight in atypical depression.
– Feeling as though the arms and legs are weighed down by lead.
– Walking, standing up, or changing position feels sluggish and heavily resisted.

It is not merely “laziness,” but a clear physical sensation that “my body is abnormally heavy.”

In summary, the winter-atypical features make people with Winter-Pattern SAD look like they’ve gone into a “hibernation mode”: eating more, sleeping more, withdrawing socially, moving less, gaining weight, and with their inner “light” visibly dimmed.

2.4 Other Risks

Even though Winter-Pattern SAD often presents with a visual tone of being “dull, slow, and heavy” rather than agitated, there are still important risks that must be monitored:

Suicidal thoughts or self-harm ideation
– These may appear explicitly (“I don’t want to be here anymore,” “It would be better if I just disappeared”).
– Or indirectly, such as neglecting one’s own health, letting physical condition deteriorate, and disregarding safety.

Even if the person has never actually attempted self-harm, the presence of such thoughts alone is a red flag that must be assessed and addressed with an appropriate care plan.

Association with Bipolar Disorder in some cases
If the same person:
– Becomes very depressed every winter,
– But in spring/summer has periods of being overly energetic, sleeping little, talking a lot, thinking quickly, spending excessively, or impulsively launching many projects,

Then this may not be just ordinary SAD, but rather a pattern of Bipolar Disorder with a seasonal pattern.

This is extremely important, because the treatment strategy—especially the use of light therapy and antidepressants—must be more cautious to avoid triggering or worsening mania/hypomania.

Diagnostic Criteria — Diagnostic Criteria (DSM-5-TR Overview)

The essence of the criteria can be summarized as:

Winter-Pattern SAD = Depression/Bipolar disorder in which the “depressive episodes” have a clearly seasonal pattern.

Therefore, when diagnosing, clinicians must be able to answer two major questions:

1. Does the person truly meet criteria for a Major Depressive Episode (MDE)?
2. Do those depressive episodes follow a seasonal pattern as defined by DSM?

3.1 Criteria for a “Depressive Episode” (Major Depressive Episode) — Expanded

To be able to label someone as having SAD, the episode in question must first meet the criteria for a Major Depressive Episode (MDE).

Core structure of MDE criteria (DSM-5-TR):

• There must be at least 5 out of 9 symptoms.
• Symptoms must persist for at least 2 weeks.

• At least one of the first two key symptoms must be present:

1. Depressed mood most of the day, nearly every day,
or
2. Markedly diminished interest or pleasure in most activities.

The 9 symptoms (summary + expansion):

1. Depressed mood (sad, empty, hopeless).
2. Markedly diminished interest or pleasure in most activities.
3. Significant weight loss or gain, or marked change in appetite.
4. Insomnia or hypersomnia.
5. Psychomotor agitation or retardation observable by others.
6. Fatigue or loss of energy.
7. Feelings of worthlessness or excessive/inappropriate guilt.
8. Diminished ability to think or concentrate, or indecisiveness.
9. Recurrent thoughts of death, suicidal ideation, suicide plans, or suicide attempts.

Additional points emphasized by DSM:

• Symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.
• The episode should not be better explained solely by a general medical condition or substance/medication effect (for example, severe hypothyroidism or side effects of certain drugs).
• It must be distinguished from normal grief reactions—for example, intense sadness immediately after the death of a loved one.

In the context of Winter-Pattern SAD, clinicians view it as:

“A full MDE that happens to occur ‘every winter’ in a patterned way.”

It is not just ordinary sadness and not the milder “winter blues.”

3.2 Criteria for “with Seasonal Pattern (Winter-Type)” — Expanded Step by Step

Once it has been confirmed that there is an MDE (or depressive episode within Bipolar Disorder), the next step is to determine whether it meets the seasonal pattern specifier.

DSM-5-TR sets the following conditions for the specifier “with Seasonal Pattern” (in plain language):

There are depressive episodes that occur in a clearly defined season.

• For example, they occur every time in late autumn–winter.
• Symptom flare-ups begin at roughly the same period each year (e.g., November–January).
• This helps differentiate from people whose depression “can occur at any time of the year” without a seasonal pattern.

There is a clear remission or significant improvement in the opposite season.

• For example, when spring–summer arrives, symptoms gradually ease even without major changes in life circumstances.
• Patients often say things like, “As the days get longer and there’s more sun, it feels like my head clears up bit by bit.”
• If symptoms never really improve throughout the year in any patterned way, it is more likely to be non-seasonal MDD.

This pattern recurs for at least 2 consecutive years.

This means that, in at least the last two years:

– Depressive episodes occurred in the same season, and

– It is not the case that one year depression was due to a breakup and another year due to job loss.

This recurrence helps establish that it is a “biologically seasonal-linked pattern”, rather than a single episode that just happened to fall in winter by coincidence.

The number of depressive episodes in the specified season must be greater than the number of episodes outside that season across the lifetime.

For example, suppose a patient has had 5 depressive episodes in their life:

– 4 occur in winter.

– 1 occurs in summer due to a severe accident.

This would still qualify as a seasonal pattern.

However, if the person has depressive episodes scattered randomly across all seasons with no tendency for clustering in one season, clinicians would be reluctant to apply the “with seasonal pattern” specifier.

The pattern must not be better explained by seasonal stressors.

This point is crucial and often overlooked:
– If someone “loses their job every winter” because their contract ends at that time → they get depressed every winter → this is better classified as depression from recurring psychosocial stress, not true SAD.
– If work always peaks at the end of the year, with overwhelming deadlines every December, and they become depressed each year at that time → this is still more consistent with stress-related depression than a pure light/biological seasonal mechanism.

Therefore, DSM emphasizes that repeated life events that just happen to occur in a particular season must be ruled out, otherwise the diagnosis may be misdirected.

Points commonly applied in clinical practice:

• Clinicians must take a detailed retrospective history, typically covering at least 2–3 years:
  – Ask for a timeline of when symptoms start and remit each year, and what life events were happening at those times.
  – If the patient cannot recall clearly, old calendars, social media photos, or input from close relatives/friends can help reconstruct the pattern.

• If a clear pattern is found, the diagnosis will usually specify:
  – “Major Depressive Disorder, Recurrent, Moderate, With Seasonal Pattern (Winter-Onset)”,
  or if it is Bipolar Disorder:
  – “Bipolar II Disorder, With Seasonal Pattern.”
  Applying the specifier correctly is not just for “academic neatness”; it has a direct impact on the treatment and prevention plan, for example:

• If we know that symptoms will flare up every late year → we can:
  – Start light therapy early, from the beginning of autumn.
  – Adjust medication or start prophylactic treatment in advance.
  – Schedule work/projects/relationships to align with seasons where mood is at higher risk.

• If we suspect bipolar with a seasonal pattern → we must prioritize mood stabilizers and use light therapy/antidepressants with particular caution.

In summary, the DSM-5-TR criteria for the seasonal pattern specifier are not simply for “tidy classification,” but to help the treatment team “view the illness as a long-term pattern” and use that pattern to design preventive and therapeutic strategies so that patients can live as well as possible in every season.

Subtypes or Specifiers — Subtypes / Ways of Specifying

Even though Winter-Pattern SAD is itself a specifier, in clinical practice the pattern is often further subdivided:

4.1 Classification by Primary Disorder

Winter-Pattern MDD

• Recurrent MDD where every depressive episode is linked to winter.
• No history of hypomania/mania.

Winter-Pattern Bipolar Disorder

• There are both depressive episodes (in winter) and hypomanic/manic episodes (commonly in spring/summer).
• Treatment must be more cautious because light therapy/antidepressants may trigger mania. Mayo Clinic+1

4.2 Classification by Additional Specifiers

Standard MDD/Bipolar specifiers can also be applied on top, such as:

• With atypical features (common in winter-SAD: hypersomnia, hyperphagia, leaden paralysis, mood reactivity).
• With melancholic features (less common but possible).
• With anxious distress — prominent anxiety in addition to depression.
• Severity: mild / moderate / severe, with or without psychotic features.
• Course: in partial remission / in full remission.

4.3 Classification by Temporal Characteristics

• Early winter-onset vs Late winter-onset — some people develop clear symptoms starting in late autumn, while others are worst in January–February. American Psychiatric Association+1
• Patterns that begin in adolescence vs those that begin in early adulthood.

Brain & Neurobiology — Brain and Biological Mechanisms

Winter-Pattern SAD is one of the mood disorders that has attracted the greatest interest in chronobiology, neuroscience, and neuroendocrinology, because it is a kind of “natural model” showing that light, time, hormones, and brain circuits can truly alter human mood at a deep systemic level.

Winter-SAD is thus not merely “people who dislike winter.”
Rather, it is a condition in which the biological clock system and the mood-regulating circuits lose their synchrony together like falling dominoes.

Below is a full-system picture in four major layers that researchers often use:

5.1 Circadian Rhythm & Phase Shift Hypothesis — The Core Axis of the Disorder

Root problem = circadian misalignment (the life clock out of sync)

In winter, “days become shorter and nights become longer.”
As a result, less light reaches the eyes, especially morning light, which is the most crucial signal for setting the SCN clock.

The brain region SCN (Suprachiasmatic Nucleus) is the master clock of the body.
It sets the timing of many systems, such as:

– Sleep

– Body temperature

– Cortisol secretion

– Melatonin secretion

– pH, metabolism, immune activity

When morning light is reduced → the SCN “resets itself more slowly” →
This leads to a phenomenon called Phase Delay (the life rhythm shifts later).

People with Winter-SAD often have a more pronounced phase delay than others, for example:

• The biological clock is telling them “it’s still time to sleep,”
  but real life demands that they get up.
• Their energy in the morning is not sufficient for functioning.
• Mood in the afternoon/evening is better than in the morning (reverse mood pattern).

Consequences for mood in the brain

When the circadian rhythm is out of sync, the limbic system responsible for mood regulation also becomes misaligned, for example:

• The amygdala becomes hyper-responsive → fear, anxiety, and sadness increase.
• The prefrontal cortex has reduced capacity to regulate emotions.
• The ACC and hippocampus function less efficiently → worsened attention, memory, and information processing.
• The reward circuit (nucleus accumbens) responds less to pleasurable stimuli.

Altogether, this produces the familiar picture of being “depressed–heavy–slow–sluggish” seen in Winter-SAD.

5.2 Melatonin & Photoperiod — Abnormal Light–Dark Hormonal Rhythms

Melatonin is a hormone secreted when the brain “perceives darkness.”
In winter, the brain secretes melatonin for longer than usual because:

• The sun rises later.
• The sun sets earlier.
• There are many days of persistent cloud cover.
• Outdoor activities are reduced.

This results in:

1) The body remaining in “Night Mode” for too long

In plain terms:
The body thinks “the night is very long” → wants to sleep more → doesn’t want to engage in activities → energy is low.

2) A delayed melatonin phase → mood decline

Melatonin is not only a sleep hormone;
it also sends signals to many systems to switch into a low-energy mode, which is associated with:

• Depressed mood.
• A sense of bodily heaviness.
• Slowed thinking.
• Reduced motivation.

3) Light Therapy = resetting the SCN clock

Morning light at around 10,000 lux
→ stimulates melanopsin → the SCN is reset earlier (phase advance)
→ melatonin secretion stops sooner → the person feels more alert and energized within 1–2 weeks.

This is why Light Therapy is the first-line treatment for Winter-SAD.

5.3 Serotonin / Dopamine & Brain Circuits — Seasonally Shifting Neurotransmitters

Winter is associated with reduced serotonin activity, supported by research:

Serotonin

• Serotonin transporter (5-HTT) activity increases reuptake → serotonin levels in the synapse decrease.
• Serotonin production in the raphe nuclei decreases.
• This leads to sad, bleak mood and a negative worldview.
• It also affects appetite regulation → increased cravings for carbs/sweets to boost tryptophan and serotonin.

Dopamine

The mesolimbic dopamine system works at a lower level:

• Motivation drops.
• Activities that previously felt enjoyable no longer feel rewarding.
• Reward sensitivity declines (“Whatever I do doesn’t feel as good as it used to”).

Summary of affected brain circuits

• Prefrontal Cortex = reduced emotional regulation.
• ACC (Anterior Cingulate Cortex) = poorer stress management.
• Amygdala = more sensitive to negative emotional signals.
• Hippocampus = worsened attention, memory, and the ability to “see a positive future.”
• Reward Circuit (VTA–NAcc) = lowered experience of pleasure and drive.

The combined result is “low mood, low energy, slowed body, slowed brain.”

5.4 Retinal Sensitivity & Genetic Factors — Light Sensitivity and Genetics

Melanopsin pathway in the eyes

Morning light stimulates retinal cells containing melanopsin
→ sends signals to the SCN to reset the internal clock.

Some people have altered sensitivity to light, such as:

• Retinal cells respond less effectively to morning light.
• The retina sends weaker signals to the SCN.
• The circadian system runs slower than in the average person.

This explains why some people become clearly depressed even after a short winter season, while others do not.

Relevant genetic factors

There is no single gene that fully explains SAD,
but research shows associations with:

• Serotonin transporter gene (5-HTTLPR)
• Melatonin receptor genes (MTNR1A / MTNR1B)
• Clock genes such as CLOCK, PER3
• Genetic predisposition to light/dark sensitivity

In summary: Winter-SAD is a disorder where “genes + biological sensitivity + seasonal winter exposure” converge.

Causes & Risk Factors — Causes and Risk Factors

Winter-Pattern SAD does not have one single cause; it is a condition that arises from multiple “layered factors” working together.

Overall, they can be divided into three main groups:

• Biological factors
• Environmental factors
• Psychological/behavioral factors

6.1 Biological Factors

1) Genetics

People who have family members with:

• SAD
• MDD
• Bipolar Disorder

have a significantly higher risk of developing Winter-SAD.

The key concept is “genetic vulnerability”:
→ Genes do not directly cause illness, but they make the person more sensitive to seasonal changes than average.

2) Easily disrupted circadian–melatonin–serotonin systems

This group has biological systems that:

• Reset their internal clock more slowly than usual.
• Are highly sensitive to changes in day length.
• Secrete melatonin for longer than average.
• Have serotonin levels that drop easily in winter.

Their brains are highly responsive to summer/winter changes, as if there is a switch turning their mood on or off.

3) Sex

Winter-SAD is found 3–4 times more often in women than in men
(likely related to sex hormones, genetics, and differential light responses).

4) Age

It is most commonly seen in the 18–30 age range,
and may improve somewhat as people grow older.

6.2 Environmental Factors

1) High latitude

Countries with extremely short winter days, such as:

• Northern Canada
• Norway
• Finland
• Northern Russia

have a much higher SAD rate than countries near the equator,
because the photoperiod (day length) is so short that circadian rhythms become heavily disturbed.

2) Excessive indoor lifestyle

Even in cities with good weather, if a person:

• Works in an office all day.
• Does not get morning sunlight.
• Commutes mainly at night.
• Lives in a dark apartment/condo.
• Sleeps late and wakes late throughout the season.

they can still develop SAD, even in countries that are not at high latitudes.

3) Long rainy/overcast seasons in tropical climates

In countries without a true winter (including Thailand):

• Prolonged rainy seasons.
• Weeks of continuous overcast skies.
• Air pollution/PM2.5 blocking sunlight.

These reduce natural light exposure → disturbing circadian rhythms in much the same way as a real winter.

4) Low temperatures – reduced activity

Cold weather leads to:

• Less exercise.
• Less desire to go outdoors.
• Overall reduced physical activity.

This affects the reward system and strengthens the depressive cycle.

6.3 Psychological & Behavioral Factors

1) Pre-existing mood disorders

People who have previously experienced depression and/or anxiety
are more likely to develop SAD, because their brains are already more vulnerable to stress and mood circuit dysregulation.

2) Environmentally sensitive temperament

Individuals who:

• Have moods that fluctuate with the weather.
• Are sensitive to darkness/rain/wind.
• Experience rapid mood drops when their daily routines are restricted.

are more easily pushed into SAD.

3) Seasonal “withdrawal” behaviors

When winter or rainy seasons arrive, they may:

• Go out less.
• Stop outdoor activities.
• Reduce social interactions.
• Spend more time alone.
• Sleep more, eat more carbs.
• Fail to maintain a consistent routine.

These behaviors create a “depression-accelerating loop” (negative behavioral loop) that pushes SAD to become more severe.

4) Accumulated stress + Seasonal stressors

Even though DSM separates Seasonal Stressors from SAD,
chronic stress still makes the brain more likely to enter a depressive episode during high-risk seasons.

Examples:

• Heavy workloads at year’s end.
• Reduced income in winter.
• Being stuck at home for long periods during the rainy season.

The overall effect is “reduced protective factors + increased triggers”, until SAD emerges.

One-picture summary

Winter-SAD arises from:

Low light → circadian rhythm disruption → prolonged melatonin → reduced serotonin/dopamine → negative shift in limbic system → low mood, low energy, reduced activity → a systematically winter-specific depression.

And its severity is determined by:

• Genetics
• Sensitivity of the circadian system
• Retinal sensitivity to light
• Strength of mood-regulation circuits
• Lifestyle during high-risk seasons
• Accumulated stress

All of these link together into a “seasonal depression mechanism” that is both predictable and preventable.

Treatment & Management — Treatment and Management

Treatment of Winter-Pattern SAD usually involves multiple approaches used together, with the main pillars being Bright Light Therapy + CBT-SAD + antidepressants when needed + lifestyle management. PsychiatryOnline+4PubMed+4PubMed+4

7.1 Bright Light Therapy (BLT) — First-Line Treatment

• Use a light box of about 10,000 lux.
• Sit approximately 30–60 cm from the box for 20–30 minutes in the morning.
• The eyes must be open, but there is no need to stare directly into the light (you can read/work during the session).
• Improvement is often seen within 1–2 weeks, but it is recommended to continue throughout the high-risk season.

Research and meta-analyses confirm that BLT is effective, and in some trials it produces results comparable to antidepressants such as fluoxetine in Winter-SAD patients. PubMed+2PubMed+2

Precautions

• In patients with Bipolar Disorder, BLT may trigger hypomania/mania and must be used under close medical supervision. Mayo Clinic+1

• Caution is required in people with severe eye diseases or those taking photosensitizing medications.

7.2 Psychotherapy — CBT-SAD

CBT-SAD (Cognitive Behavioral Therapy for SAD)

• Restructures beliefs about winter (from “winter = a wrecked season” to “winter = a season that requires special self-care planning”).
• Trains behaviors that increase light exposure and meaningful activities during the high-risk season.
• Teaches skills for managing repetitive negative thoughts and tendencies to isolate.

Research indicates that CBT-SAD is no less effective than BLT in the short term, and in some studies may provide better protection against relapse in subsequent winter seasons. PsychiatryOnline+1

7.3 Pharmacotherapy — Antidepressants

• Used similarly to standard MDD treatment, such as SSRIs (sertraline, fluoxetine, etc.).
• Some guidelines recommend bupropion XL, started before the high-risk season, to prevent depressive episodes in people with a clear seasonal pattern. AAFP+1
• In Bipolar Disorder, mood stabilizers must lead the treatment plan, and antidepressants/BLT must be used with caution.

7.4 Lifestyle & Self-Management

• Get morning sunlight as much as the context allows; even on cloudy days, natural light can help reset the biological clock. urmc.rochester.edu+1
• Maintain a consistent sleep–wake schedule (going to bed and waking up at the same time every day).
• Exercise regularly, especially outdoors.
• Social: schedule activities with friends/family in advance during high-risk seasons to prevent isolation.
• Nutrition: plan meals to reduce carb binges, and emphasize protein and fiber to help balance weight and energy.

There is research on vitamin D, but evidence remains inconclusive regarding its direct benefit for SAD; it is more commonly used to correct deficiency if present, rather than as a stand-alone SAD-specific treatment. NCBI+1

7.5 Prevention & Monitoring

People who know they become depressed every winter can:

• Schedule follow-up appointments with psychiatrists/therapists before the season begins.
• Start BLT and/or preventive medication in advance.
• Create a personal “Winter Care Plan” (sunlight schedule, social plans, hobbies/projects, etc.).

Notes — Additional Key Points

Winter-Pattern SAD ≠ “just disliking winter.”
The condition must reach the level of a “depressive episode” that clearly disrupts real life and meets the DSM seasonal-pattern criteria.

It must be distinguished from life situations.
If someone becomes depressed every year because of year-end peak workloads, or because they always stay home during school breaks, this fits better with “depression with seasonal stressors” than with true SAD.

Be cautious about Bipolar Disorder.
If the history includes periods in other seasons with very elevated mood, little sleep, pressured speech, or heavy spending, Bipolar Disorder must be considered, and light boxes + antidepressants should not be used aggressively without mood stabilization.

Light or vitamins should not substitute for proper assessment.
Relying only on light or supplements without adequate evaluation risks underestimating severity, especially when suicidal ideation is present.

Tropical country context.
Seasonal patterns can still exist and be linked to:

• Long rainy seasons with overcast skies.
• Seasons when daily routines change (e.g., extended periods spent indoors in dorms/offices).

But clinicians must always assess whether the pattern is due to “light and circadian changes” or to “socioeconomic/psychosocial stressors.”

📚 References

(Compiled from research articles and clinical guidelines used in real-world practice for mood disorders and chronobiology.)

• American Psychiatric Association (APA).

Diagnostic and Statistical Manual of Mental Disorders, 5th Edition, Text Revision (DSM-5-TR).
– Section on Major Depressive Disorder – With Seasonal Pattern (Specifier)
– Explains SAD diagnostic criteria and differences from seasonal stressors.

• Rosenthal NE, Sack DA, Gillin JC, et al. (1984).

“Seasonal Affective Disorder: A Description of the Syndrome and Preliminary Findings With Light Therapy.” Archives of General Psychiatry.
– The classic first paper defining SAD and demonstrating the effects of Light Therapy.

• Lam RW, Levitt AJ, et al. (2006).

“The Can-SAD Study: Light Therapy vs Fluoxetine in the Treatment of Seasonal Affective Disorder.” American Journal of Psychiatry.
– An RCT comparing Light Therapy with fluoxetine.

• Rohan KJ, Lindsey KT, Roecklein KA, et al. (2015, 2022 follow-up).

“Cognitive-Behavioral Therapy vs Light Therapy for SAD.” American Journal of Psychiatry.
– Shows the effectiveness of CBT-SAD and its role in preventing relapse in subsequent seasons.

• Pjrek E, Winkler D, Konstantinidis A, et al. (2020).

“The Efficacy of Light Therapy in SAD: Meta-analysis.” Psychotherapy and Psychosomatics.
– Summarizes robust evidence that BLT is effective for SAD.

• Lewy AJ, Kern HA, Rosenthal NE, et al.

“Shifted Melatonin Rhythm in SAD.”
– Foundational work for the Phase Shift Hypothesis: SAD arises from circadian delay.

• Levitan RD (2007).

“The neurobiology of seasonal affective disorder.” Dialogues in Clinical Neuroscience.
– One of the most in-depth descriptions of the serotonin–melatonin–circadian mechanism.

• Mayo Clinic. Seasonal Affective Disorder.

– Patient-facing guide based on APA and current clinical guidelines.

• Rodgers JL et al. (2018–2023).

A body of chronobiology research examining melanopsin, the SCN, and photoperiod effects on mood.

• National Institute of Mental Health (NIMH).

– The Seasonal Affective Disorder page and diagrams of circadian–light pathways.

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