Seasonal affective disorder (SAD) is now more commonly known as major depressive disorder with seasonal pattern. It is a type of depression that tends to affect people who live in countries farther from the equator. It is most common during the winter months and tends to resolve in springtime.

Other names for major depressive disorder with seasonal pattern include SAD, winter depression, and seasonal depression.

According to the American Psychiatric Association (APA), the condition affects about 5% of people in the United States.

Symptoms can last for approximately 40% of the year.

In this article, we look at how this condition develops, who might be at risk, and the available treatment options.

A man who suffers from seasonal affective disorder walking down a foggy roadShare on Pinterest
SAD is a seasonal condition that tends to affect people during the winter months.

People with SAD, or major depressive disorder with seasonal pattern, experience symptoms of depression with gradually increasing frequency as days start getting shorter. These symptoms slowly improve in early spring, as the amount of sunlight increases.

The APA suggest that this condition might occur when reduced exposure to sunlight triggers a chemical imbalance in the brain. However, more research is necessary to confirm the cause.

Seasonal changes in sunlight affect the circadian rhythms that regulate a person’s sense of time. Some people consider this to be their “internal biological clock,” and disruption to the circadian rhythm can significantly disrupt mood.

According to Harvard Medical School, women experience SAD more often than men. SAD also develops in young people more often than in older adults.

It is also more common in people who live farther north of the equator, as winter further reduces the hours of daylight in these locations.

Less commonly, some people experience SAD during the summer months.

The symptoms of SAD are similar to those of depression. The major difference is that symptoms develop as winter approaches and resolve during springtime.

Most people’s symptoms occur and resolve at the same time every year.

Symptoms are usually mild as autumn advances and the hours of daylight start to decline. The severity, characteristics, and patterns of SAD can vary considerably from person to person.

The signs and symptoms of SAD tend to include:

  • anxious feelings that are out of proportion with their cause or trigger
  • feelings of guilt and worthlessness
  • stress and irritability
  • difficulties in making decisions
  • reduced concentration
  • consistent low mood
  • reduced libido
  • restless activity, such as pacing
  • crying, often with no apparent trigger
  • feelings of fatigue, even after a full night’s sleep
  • sleeping for too long
  • increased appetite
  • social withdrawal and a reduced interest in activities that once provided pleasure
  • difficulty concentrating
  • overeating and possible weight gain
  • suicidal ideation

A doctor may not diagnose this condition in people who experience SAD as an effect of seasonally related psychosocial stressors. For instance, people who work seasonally may not have employment during the winter, and they may exhibit some symptoms of depression as a result.

Some people experience these symptoms during the summer rather than the winter, with symptoms resolving during the wintertime. However, the most common presentation of SAD occurs during the winter months.

Certain factors can affect a person’s risk of developing SAD. We discuss these in more detail below:


Women are more likely than men to experience SAD, though this may be due to the higher prevalence of overall depression among women.

According to a 2015 overview in the journal Depression Research and Treatment, diagnoses of SAD are four times more common in women than men.


The National Institute of Mental Health (NIMH) suggest that living farther from the equator can increase the risk of developing SAD.

People who live in places where the days are much shorter in winter are more susceptible.

Family history

Having close relatives with a history of other types of depression can increase the likelihood that SAD may develop.

Personal history of depression

People with a history of depression or bipolar disorder, as well as those who currently have either of these conditions, are more likely to develop SAD.

However, a doctor will only reach a diagnosis of SAD if depression symptoms become more common during a particular season each year.

Experts are still unsure of the exact causes of SAD. However, studies have pointed to the following factors:

Reduced serotonin production during winter

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A person’s serotonin production usually drops during the winter.

Serotonin is a neurotransmitter that plays a key role in moderating mood. It binds to a particular protein to travel around the body.

Levels of this protein usually drop during the winter months to protect a person against the environmental stress of the season.

However, one 2016 longitudinal study in the journal Brain found that people with SAD do not experience a decrease in serotonin transporter levels during winter. The risk is especially high in people who are prone to affective disorders.

Disrupted melatonin levels

Melatonin is a hormone that influences sleep patterns and mood.

The NIMH maintain that reduced exposure to sunlight during winter’s shorter days disrupts the balance of melatonin in the body.

Reduced vitamin D production

A 2018 study in rats, the results of which appear in the journal Genes & Nutrition, found links between vitamin D and serotonin that could explain the onset of depression in some people.

The body produces vitamin D after exposure to sunlight. Getting less sunlight during the winter months might explain the cycle of depressive symptoms that characterize SAD.

The doctor may ask the following questions to identify whether or not SAD is present:

  • How long has the person been experiencing symptoms?
  • How severe are the symptoms?
  • How do they affect daily activities?
  • Have there been any changes in sleeping or eating patterns?
  • Can the person identify a shift in thoughts and behaviors during different seasons?
  • Can they provide information on any relevant family medical history, such as a close family member with depression, bipolar, or other affective disorders?

Because there are several types of depression, it might take some time for a doctor to diagnose SAD accurately. No medical or laboratory test is available for diagnosing this condition. However, the doctor may order some diagnostic tests, including blood tests, to rule out other illnesses or underlying conditions.

The APA do not class SAD as a separate disorder in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). Instead, SAD is a “course specifier.”

A healthcare professional will only diagnose SAD if a person has symptoms of major depressive disorder that develop and resolve at specific times each year.

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Light therapy can help treat SAD.

According to the APA, a person may be able to alleviate SAD symptoms by increasing their exposure to sunlight. For example, going for long walks when there is still some sunlight could help.

Treating SAD usually involves medication, therapy, and lightbox therapy.

Lifestyle adjustments can also help reduce the impact of SAD.


Although SAD seems to occur due to changes in brain chemistry, therapy that focuses on mood and behavior can also help. The APA suggest that this type of therapy may have a longer lasting benefit than taking medications or using a lightbox to manage mood.

Cognitive behavioral therapy (CBT) can help people monitor and control their reactions to certain situations and environments more successfully. If a person can alter the way they perceive events, their behavior will also change with time.

This may help reduce the severity of their symptoms during the season in which the effects of SAD peak.

A course of CBT usually includes an individual program of thought and breathing exercises to help a person identify and moderate negative feelings.

People can attend group or partner sessions of CBT. Such sessions provide support and advice to those who live with people with SAD.


A healthcare provider may prescribe an antidepressant, usually a selective serotonin reuptake inhibitor. This type of medication increases serotonin levels.

The Food and Drug Administration (FDA) have now approved bupropion (Wellbutrin XL) for specific use by people who have SAD.

People should always follow their doctor’s instruction when taking these drugs and check the prescribing information for side effects and potential risks.

In this article, learn more about antidepressants.

Bright light therapy

If a person’s symptoms are severe enough to impact daily function, a doctor may recommend bright light therapy.

Also known as phototherapy, this intervention can help restore a person’s circadian rhythms.

In bright light therapy, a person sits in front of a specialized lightbox for a set amount of time every day between early fall and spring. Ultraviolet lamps, full spectrum lights, and tanning lamps will not have the same effect for people with SAD.

The NIMH recommend engaging in lightbox exposure as soon as possible after waking up.

In general, people should receive light therapy for 20–60 minutes per day, depending on the strength of the light.

Lifestyle choices

Some people with SAD find that increasing their exposure to natural sunlight can help alleviate symptoms. Examples include opening blinds and curtains, trimming trees around the house, and sitting closer to the window during the daytime.

Getting outside every day for a long spell in the open air may help, as might staying social and active. The seasonal nature of SAD means that planning activities ahead of the season can help reduce its impact on everyday life.

Similarly, maintaining regular exercise and a balanced, nutritious diet are great for overall health. They might also help a person alleviate symptoms of anxiety and support a more regular sleep cycle.


Can seasonal depression turn into a type that occurs all year round?


According to the APA, a healthcare professional must diagnose SAD, or major depressive disorder with seasonal pattern, in subsequent episodes.

There must be a seasonal relationship between the onset of a major depressive episode and a particular time of the year, such as fall or winter.

With this in mind, symptoms can occur at any time and may persist after the symptoms of the depressive episode have improved (for instance, in the summer). However, for people whose episode began in fall or winter and did not resolve in the summer, it would be major depressive disorder. Careful recordkeeping of symptoms may help the person’s mental health provider define the type of major depressive disorder they have and suggest an appropriate treatment plan.

Timothy J. Legg, PhD, CRNP Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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