Seasonal Affective Disorder Fast Facts

Seasonal Affective Disorder (SAD) is a mental health disorder characterized by depression that only affects the sufferer during a particular season of the year.

SAD affects an estimated 10 million Americans.

Women are four times more likely than men to be affected by SAD.

SAD most often occurs in young adults between the ages of 18 and 30.

SAD is more prevalent in some geographic areas than others.

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SAD affects an estimated 10 million Americans.

What is Seasonal Affective Disorder?

Seasonal affective disorder (SAD) is a mental health disorder closely related to major depressive disorders. SAD is not considered a distinct disorder on its own but rather a sub-type of major depression. SAD is characterized by depressive symptoms that only occur during a specific season of the year and disappear during other seasons.

For most people, SAD occurs during the late fall and winter and goes away in the spring and summer. In some cases, sufferers may experience SAD in the spring or summer rather than in the winter, but these cases are rare.

SAD is most common in geographic areas far away from the Earth’s equator, either to the north or the south. These areas have longer, colder, darker winters than areas near the equator, leading scientists to believe that the geographic conditions either partly cause symptoms or make them worse. The prevalence of SAD can vary significantly over relatively small geographic distances. Rates of SAD are nearly ten times higher in New England, for example, than in Florida.

Symptoms of Seasonal Affective Disorder

Most symptoms of SAD are similar to those of major depressive disorder. Common symptoms include:

  • Low, sad mood throughout the day on most days
  • Low energy
  • Feelings of hopelessness
  • Feelings of worthlessness
  • Loss of interest in previously enjoyable activities
  • Sleep disruptions
  • Mental fogginess
  • Changes in appetite or weight
  • Suicidal thoughts

Some symptoms are more common in winter-pattern SAD. They include:

  • Sleeping too much
  • Fatigue
  • Withdrawal from social interaction
  • Increased appetite, especially cravings for foods high in carbohydrates
  • Weight gain

Symptoms of the less common summer-pattern SAD often include:

  • Insomnia
  • Restlessness
  • Loss of appetite
  • Weight loss
  • Anxiety

What Causes Seasonal Affective Disorder?

Scientists don’t yet know exactly what causes SAD. Studies have found an association between SAD and several biochemical factors, but none of them have been definitively pinpointed as the cause. SAD may result from a combination of biochemical triggers, and different individuals might react differently to various triggers.

Some possible SAD risk factors include:

  • Serotonin. Serotonin is a brain chemical called a neurotransmitter. It is essential for normal mood regulation, and people who suffer from SAD could have serotonin levels that fluctuate seasonally.
  • Melatonin. Melatonin is a hormone that helps regulate sleep patterns. Your body produces more melatonin when it’s dark, so the short winter days may lead to high melatonin levels. This, in turn, may contribute to feelings of lethargy and low mood.
  • Vitamin D. Vitamin D is thought to play an important role in serotonin regulation. The body produces vitamin D naturally when exposed to sunlight. Since sunlight is relatively scarce in the winter, SAD sufferers may have insufficient levels of the vitamin.

Changes in sunlight exposure affect everyone who lives in a particular place, but not everyone suffers from SAD. This suggests that some people are more susceptible to geographically influenced risk factors than others. Some factors that put people at higher risk of developing SAD include:

  • Sex. SAD is much more common in women than in men.
  • Age. SAD is more common in younger adults than in older adults.
  • Family history. People who have a close relative with SAD or another depressive disorder are at higher risk of SAD.
  • Having certain other mental illnesses. People who suffer from major depressive disorder or bipolar disorder are at risk of having their symptoms get worse seasonally. SAD sufferers often suffer from another mental health disorder, such as attention-deficit/hyperactivity disorder (ADHD), eating disorders, or anxiety disorders.

Is Seasonal Affective Disorder Hereditary?

SAD may have an inherited component, but scientists have not yet identified a clear association between genetics and increased risk for the disorder. The risk of developing the condition is greater for someone who has a first-degree relative (a parent or a sibling) with SAD, but about 85% of SAD sufferers do not have a first-degree relative with the disorder.

Some studies have found that a large percentage of SAD sufferers have a relative with another mental disorder such as major depressive disorder or schizophrenia. This could suggest a common genetic component associated with SAD and these disorders, but no studies have found a definite connection.

How Is Seasonal Affective Disorder Detected?

SAD often co-exists with other mental disorders, and both SAD and its co-existent disorders can lead to potentially severe physical, psychological, social, and professional complications. For these reasons, early detection of SAD’s symptoms is essential. Prompt treatment can help reduce your risk of serious complications.

Common early signs of SAD and other depressive disorders include:

  • Loss of interest in pleasurable activities
  • Lethargy, fatigue, or oversleeping
  • Pessimism or hopelessness
  • Changes in appetite
  • Anxiety
  • Irritability
  • Recurrent thoughts about death

How Is Seasonal Affective Disorder Diagnosed?

To confirm or rule out a diagnosis of SAD, a doctor will typically begin with a physical exam to look for signs of physical conditions that could be causing the symptoms. The doctor may also order blood tests or other laboratory tests to further rule out physical explanations.

If no other causes are found, you may be referred to a mental health professional for a psychological evaluation. The mental health provider will look for signs of depressive disorder and will compare your symptoms to the diagnostic criteria for SAD.

To be differentiated from major depressive disorder and diagnosed as SAD, your symptoms must meet several criteria, including:

  • The symptoms must meet all the criteria for a diagnosis of major depression.
  • The symptoms must begin at a specific time of year and go into remission at a different particular time of year.
  • The symptoms must have occurred in the seasonal pattern for the previous two years.
  • Seasonal depressive episodes must outnumber non-seasonal depressive episodes.


How Is Seasonal Affective Disorder Treated?

Treatment of SAD typically utilizes both medication and non-drug-based therapies. Treatment approaches include:

  • Medication. SAD is commonly treated with antidepressant drugs. Selective serotonin reuptake inhibitors (SSRIs) such as citalopram, escitalopram, fluoxetine, paroxetine, and sertraline help regulate serotonin levels. A newer type of antidepressant called bupropion has also been approved to treat SAD, and it may be prescribed for those who don’t respond to SSRIs or who are sensitive to those drugs’ side effects.
  • Light therapy. This type of therapy is designed to compensate for decreased exposure to sunlight during the winter. The patient typically sits in front of a lightbox that emits bright artificial light. Lightbox sessions generally are done first thing in the morning for 20-60 minutes.
  • Vitamin D supplements. Vitamin D is not recommended as the only treatment for SAD, and studies of its effectiveness at treating the disorder have had mixed results. However, if you are deficient in vitamin D, taking supplements might be recommended.
  • Psychotherapy. A type of talk therapy called cognitive behavioral therapy (CBT) is often recommended for SAD patients. CBT focuses on recognizing the thought patterns that accompany depressive symptoms and developing behavioral strategies for dealing with those patterns.

How Does Seasonal Affective Disorder Progress?

Left untreated, SAD (and all depressive disorders) can severely impact the sufferer’s life. Symptoms may worsen over time, and in 40% of cases, depressive symptoms stop going into remission at the end of the season. In these cases, the diagnosis is typically changed to major depressive disorder or bipolar disorder.

Long-term impacts of SAD can include:

  • Struggles at work or school
  • Problems with relationships
  • Substance abuse
  • Development of other mental health disorders
  • Suicidal thoughts or suicide attempts

How Is Seasonal Affective Disorder Prevented?

The cause of SAD is not well understood, so there is no guaranteed way to prevent the disorder. However, you can take steps to decrease your exposure to risk factors. Consider taking these precautions, especially if you think you are at risk of SAD:

  • Increase your exposure to sunlight in the winter. Get outside whenever possible on sunny days, and spend time near sunny windows when you’re inside. However, ask your doctor how to protect yourself from overexposure to ultraviolet light, which increases the risk of skin cancer.
  • Keep a healthy sleep routine. Avoid sleeping too much during the winter so that you can maximize your daytime waking hours.
  • Get plenty of exercise.
  • If the winter season has a serious impact on your mood every year, consider moving to a sunnier climate.

Seasonal Affective Disorder Caregiver Tips

If you’re caring for someone affected by SAD, keep these tips in mind:

  • Recognize the disorder for what it is. SAD isn’t merely “the winter blues.” While most of us who live in a dreary winter climate get cabin fever during the colder months, SAD is more than just a longing for spring. It is a manifestation of major depressive disorder, a potentially debilitating mental health-related issue. Learn as much as you can about the condition to understand the effect it is having on your loved one.
  • Counter the impact of the season. It won’t help to simply tell your loved one to cheer up. It might help, however, if you encourage activity and create an active, light-filled environment. Don’t judge or badger your loved one. Instead, provide a context that can help them cope with their symptoms.
  • Get help. Don’t accept the symptoms of SAD as the inevitable consequences of the season. Encourage your loved one to seek help from medical or mental health professionals and be supportive of their treatment for SAD.

SAD often exists alongside other mental health and brain-related conditions, a situation called co-morbidity. Here are a few of the disorders commonly associated with SAD:

Seasonal Affective Disorder Brain Science

Researchers are trying to find more effective ways to treat SAD, and part of that quest is working to understand better how our moods are affected by changes in the season. Numerous studies have pursued theories of brain chemistry and neurology that might explain why SAD occurs. Recent studies have included:

l An international team of researchers has explored the possibility that SAD sufferers cannot regulate their serotonin levels in a seasonally appropriate way. Usually, the body regulates its serotonin levels to maximize the amount of the chemical available in the winter. This study found that some SAD sufferers had an atypical serotonin regulation system in certain parts of their brains during winter. The study also found evidence that this atypical pattern might be associated with a specific genetic variation.

l Two recent studies have found evidence that special light-sensing cells in our eyes are designed to communicate with the parts of our brain that regulate mood. This system’s effect seems to be why we are prone to depressed moods in the winter when there is less light. Although the researchers do not understand the purpose of this psychological dependence on light, the discovery seems to explain why light therapy is effective at treating SAD.

Seasonal Affective Disorder Research

Title: Optimizing Long-Term Outcomes for Winter Depression With CBT-SAD and Light Therapy

Stage: Recruiting

Principal investigator: Kelly J Rohan, PhD

University of Vermont, Psychology Department

Burlington, VT 

Winter seasonal affective disorder (SAD) is a subtype of recurrent depression involving major depressive episodes during the fall and/or winter months that remit each spring. The central public health challenge in the management of SAD is the prevention of winter depression recurrences. This application focuses on two SAD treatments that each work for some patients: light therapy (LT) and a SAD-tailored group cognitive-behavioral therapy (CBT-SAD).


Title: Antidepressant Discontinuation in Treatment Resistant Depression

Stage: Recruiting

Principal investigator: Rifaat S. El-Mallakh, MD

The University of Louisville, Department of Psychiatry and Behavioral Sciences

Louisville, KY 

The purpose of this study is to compare the effects on depressive symptoms of subjects who discontinue serotonergic antidepressants (a certain type of antidepressant, such as Prozac, that works on serotonin receptors in the brain) with the effects on depressive symptoms of subjects who continue to take serotonergic antidepressants. During this study, subjects will also be presented with the opportunity to undergo genetic testing for the serotonin gene transporter with a short or long form. This is being done because it has been demonstrated that genetic testing improves outcomes while treating treatment-resistant depression.


Title: Promoting Enhanced Pharmacotherapy Choice Through Immunomarkers Evaluation in Depression (PRECISE-D)

Stage: Active, Not Recruiting

Principal investigator:  Madhukar H Trivedi, MD

University of Texas Southwestern Medical Center

Dallas, TX

PRECISE-D is a single site, randomized, open-label 8-week clinical trial that will enroll 70 participants to evaluate if the inflammation level in our body can predict how we will respond to antidepressants. C-reactive protein (CRP) is a substance in the body that is associated with inflammation. Previous research has suggested that people with high CRP (i.e., high inflammation levels) tend to have greater improvement of depressive symptoms with an antidepressant called bupropion, while individuals with low CRP (i.e., low inflammation levels) appear to have more benefit from selective serotonin reuptake inhibitors antidepressants (SSRI), such as escitalopram. However, it is not completely clear if CRP can predict your response to these two antidepressants.

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