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Seasonal affective disorder (SAD) is another term for major depressive disorder (MDD) with seasonal pattern. It’s a type of depression that’s provoked by seasonal change. Usually, symptoms begin in the fall or winter.

The condition affects between 0.5 and 2.4 percent of people in the United States. SAD most often occurs in women and young adults, particularly those who live farther north.

Symptoms of SAD most commonly begin around late fall or early winter and end in the spring. However, it’s possible to experience symptoms at other times of the year. You also may not experience the condition every year.

In general, there are two types of SAD: winter-pattern and summer-pattern. Summer-pattern SAD occurs in around 10 percent of cases.

Symptoms of either pattern last around 4 to 5 months, and may include:

Symptoms of winter-pattern SAD may additionally include:

On the other hand, symptoms of summer-pattern SAD may include:

The exact cause of SAD is unknown. Contributing factors may vary from person to person.

Light is thought to influence SAD. One theory is that decreased sunlight exposure in winter and increased exposure in the spring and summer affects the natural biological clock that regulates hormones, sleep, and moods. Individuals affected by SAD may have difficulty regulating their biological clock, known as the circadian rhythm.

Abnormal levels of the hormones serotonin and melatonin in people with SAD may also disrupt their circadian rhythm. According to research from 2016, SAD appears to be more likely in people whose brains maintain high levels of serotonin transporters, leading to lower levels of serotonin.

People with SAD may also produce overly high amounts of melatonin, a hormone that controls and promotes sleep.

Learn more about seasonal depression symptoms, causes, and treatments.

People who live in areas that have long winter nights (due to higher latitudes) and less sunlight are more likely to experience SAD. For example, the condition is more common in Canada and Alaska than in sunnier Florida.

The condition occurs more frequently in women than men, and it’s most likely to begin in younger adults between the ages of 18 and 30.

People with a family history of SAD and other psychological conditions are at greater risk for SAD.

Additionally, individuals with other mental health conditions are more likely to experience SAD. Around 25 percent of people with bipolar disorder and between 10 to 20 percent of people with major depressive disorder also have SAD.

A doctor or mental health care professional will ask you several questions about your symptoms and when you first noticed them.

A diagnosis of SAD requires the following:

  • depression symptoms
  • episodes that occur only during a specific season for at least 2 years in a row
  • frequent depressive episodes during that particular season

If you have only minor mood changes with the seasons, you may have subsyndromal seasonal affective disorder instead of SAD.

If your symptoms continue past the change in season, your diagnosis may be changed to bipolar disorder or major depressive disorder.

SAD can be treated with counseling, medications, and therapy.

One common treatment, cognitive behavioral therapy (CBT), can help people with SAD learn to focus on positive thoughts and activities rather than negative ones.

Some people also benefit from medications such as antidepressants. These may include:

Talk with your doctor about which medication may be best to treat your symptoms.

Vitamin D supplements are sometimes used to treat SAD as well. However, some research indicates that these supplements may not be effective, and more studies need to be done.

Healthy lifestyle habits, like getting regular exercise and sun exposure, may also help minimize SAD symptoms.

Light therapy

Another treatment for wintertime SAD is light therapy. This involves using a specialized light box for at least 30 minutes each day during the winter to replicate natural light.

Side effects of light therapy may include dizziness, eye fatigue, or headaches. You may need to avoid light therapy if you:

  • have certain eye diseases
  • recently had eye surgery
  • are sensitive to light due to other medications
  • have bipolar disorder

Another similar treatment option is a dawn simulator. It uses a timer-activated light to mimic the sunrise, which helps to stimulate the body’s clock.

Light therapy should be used only under a doctor’s supervision and on approved devices. This therapy may work best in combination with other treatments, like medications.

If you experience symptoms associated with SAD, see a doctor, counselor, or psychiatrist. This is especially important if your symptoms are impacting your everyday life.

Since SAD usually occurs on a regular schedule, you may also consider talking with your doctor before symptoms return to see if early treatment can help prevent them.

If you have thoughts of wanting to harm yourself or others, or feel that life is no longer worth living, seek immediate medical attention or call the National Suicide Prevention Lifeline at 800-273-TALK (8255) for more information.

If you regularly feel depressed and have difficulty sleeping during certain seasons, especially the winter, you may be experiencing SAD.

Treatments like counseling, medications, and light therapy are often effective for reducing SAD symptoms. Increasing your exercise and natural light exposure may also help.

If you have symptoms of SAD, talk with your doctor. They can work with you to create a treatment plan to best manage the condition.