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What is seasonal affective disorder?

Many people have experienced a case of the “winter blues”. After all, you’re stuck inside, it gets dark early, and the weather may be cloudy and gray for days on end.

But if those sad or listless feelings last, and the winter months really start getting you down, you might have something more than just the winter blues. In other words, you may be suffering from seasonal depression, also known as seasonal affective disorder (SAD).

Seasonal affective disorder is a mood disorder, caused by changing seasons. It happens to sufferers every year at approximately the same time. In general, seasonal affective disorder starts in fall or winter and ends in spring or early summer. A less common form of SAD, known as "summer depression”, begins in late spring or early summer and ends in fall.

Those who suffer from SAD generally feel tired, sad, have negative thoughts and are without motivation. Statistics show that about 5% of adults in the United States experience SAD. Symptoms tend to start in young adulthood. SAD affects women more than men, though it’s not clear why.

Fortunately, treatment can help those who suffer from seasonal affective disorder overcome their symptoms and return to normal life.

Symptoms of seasonal affective disorder

For most sufferers, seasonal affective disorder symptoms appear during late fall or early winter. They tend to go away during the sunnier days of spring and summer. Less commonly, some people’s symptoms begin in spring or summer.

No matter what time of year symptoms begin, symptoms may start out mild and become more severe as the season progresses.

Typical symptoms of seasonal affective disorder may include:

  • Feeling depressed, unhappy or “down” most of the day
  • No interest in regular activities
  • Sleeping problems, either insomnia or oversleeping
  • Low energy
  • Appetite or weight changes
  • Feeling sluggish, heavy or agitated
  • Difficulty concentrating on daily tasks
  • Feeling worthless, hopeless or guilty
  • Having thoughts of death or suicide

Importantly, these symptoms can have further negative effects on daily life, including:

  • Social isolation or withdrawal
  • Problems with school or work
  • Problems in relationships
  • Feelings of boredom and loneliness

If you experience any of these symptoms without relief, it is important to make an appointment to see a doctor or therapist.

Seasonal affective disorder causes

Despite research into the mental health disorder, the specific cause of seasonal affective disorder remains unknown.

However, there are certain factors which are thought to play a role in the development of SAD. These include:

  • Changes to your internal clock (circadian rhythm). In winter, the days get shorter and sunlight grows weaker. This decrease in sunlight is thought to disrupt some people’s internal clocks or “body clocks”, leading to feelings of depression.
  • Changes to serotonin levels in the brain. In some people, reduced sunlight can cause a drop in serotonin levels in the brain. Serotonin is an important neurotransmitter that helps stabilize mood.
  • Not getting enough vitamin D. Serotonin also gets a boost from vitamin D. Since exposure to sunlight helps us produce vitamin D, less sun in the winter can lead to a vitamin D deficiency. That change can affect serotonin and mood.
  • Melatonin levels. The change in season can also disrupt the balance of the body's level of melatonin, which plays a role in sleep patterns.

Seasonal affective disorder risk factors

While no one is certain of the specific causes of SAD, there are a number of risk factors that may increase your risk of seasonal affective disorder. These include:

  • Genetics and family history. People with SAD are more likely to have relatives with SAD or another form of depression, showing a possible genetic link for developing the condition.
  • Having pre-existing depression or another psychiatric condition, such as bipolar disorder. Symptoms of depression may be worse if you have conditions like these.
  • Where you live. SAD appears to be increasingly more likely the further one lives away from the equator. This may be due to decreased sunlight during the winter and longer days during the summer months.

Diagnosis and treatment of seasonal affective disorder Diagnosis

It can be difficult to distinguish seasonal affective disorder from other mood disorders and types of depression. To make an accurate diagnosis, your doctor will likely perform some or all of the following:

  • A physical exam, in order to rule out any underlying health issues.
  • Lab tests. For example, your doctor may do a blood test called a complete blood count (CBC) or test your thyroid to make sure it's working correctly.
  • Psychological evaluation. To check for signs of depression, your doctor will ask about symptoms, thoughts, feelings and behavior patterns. You may be asked to fill out a questionnaire to help answer these questions.


In general, there are three different types of treatment for SAD. Your doctor may recommend one, two or all three.

Treatment types include:

  • Light therapy
  • Medications (antidepressants)
  • Psychotherapy

Light therapy

Light therapy involves exposure to a special light box (which emits a bright light) soon after waking each day. Light therapy mimics natural outdoor light and appears to cause a change in the brain chemicals linked to mood.


Some people with SAD benefit from taking antidepressants, especially if symptoms are severe.

Keep in mind that it may take several weeks to notice the full benefits from an antidepressant.


Psychotherapy, also called talk therapy, is another option to treat SAD. A particular type of psychotherapy known as cognitive behavioral therapy is particularly beneficial for learning helpful ways to cope with symptoms and make positive changes.

Self-care for seasonal affective disorder

In addition to the treatments above, it is also beneficial for people suffering from SAD to make small environmental changes, and take care of themselves and perform positive, mood-elevating activities such as:

  • Make your environment sunnier and brighter. Open blinds and curtains and cut back tree branches that block sunlight into your home.
  • Go outside. Take a long walk, walk your dog, or simply sit outside and enjoy some fresh air. Even on cold or cloudy days, outdoor light can help — especially if you spend some time outside within a short time of getting up in the morning.
  • Exercise regularly. Exercise and other types of physical activity help relieve stress and anxiety, both of which can increase SAD symptoms.

Other beneficial activities can include:

  • Relaxation techniques such as yoga or tai chi
  • Meditation
  • Guided imagery
  • Music or art therapy

While it can feel debilitating to suffer from seasonal affective disorder, the good news is that it is easy to seek help, get the right treatment, and start the path to recovery.


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Can a lack of vitamin D cause seasonal affective disorder?

While the specific causes of SAD are not totally understood, it is thought that a vitamin D deficit can indeed lead to SAD symptoms. The reason is that serotonin production in our bodies is stimulated by vitamin D. Since sunlight helps us produce vitamin D, less sun in the winter can lead to a vitamin D deficiency. That change can affect serotonin and mood.

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Can I take an online test to see if I have seasonal affective disorder?

Yes. If you feel that you may suffer from some of the symptoms of seasonal affective disorder, there are a number of online self-assessment seasonal affective disorder tests you can use to check whether you may be suffering from SAD.

In general, SAD assessments take the form of a short questionnaire that only takes a few minutes to complete. Many of the assessments include questions on a scale rating of 1-5 for you to choose from.

If, after taking a test, you discover that you might be suffering from seasonal affective disorder then you should contact your doctor immediately so that they can confirm or deny a diagnosis and suggest the best course of treatment.

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What is light therapy for seasonal affective disorder?

Since the 1980s, light therapy has been regularly used in the treatment of seasonal affective disorder. It aims to expose people with SAD to a bright light every day to make up for the lack of natural bright sunshine in the colder months.

For this treatment, the person sits in front of a very bright light box every day for about 30 to 45 minutes, usually first thing in the morning, from fall to spring. The light boxes, which are about 20 times brighter than ordinary indoor light, filter out potentially damaging UV light, making them safe to use. However, people with certain eye diseases or people taking certain medications that increase sensitivity to sunlight may need to use alternative treatments or use light therapy under medical supervision.

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What are some of the most common symptoms of seasonal affective disorder?

Common symptoms of seasonal affective disorder include:

  • Low mood, low self-esteem
  • Loss of interest or pleasure in activities you used to enjoy
  • Appetite and weight changes
  • Changes in sleeping pattern
  • Difficulty concentrating on regular tasks
  • Fatigue and lack of energy
  • Use of drugs or alcohol for comfort
  • Feeling angry, irritable, stressed, or anxious a lot of the time
  • Unexplained aches and pains
  • Feelings of sadness, hopelessness, and despair
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Can seasonal affective disorder happen in summer?

While most SAD sufferers experience symptoms during the winter months, a small proportion of people experience symptoms during summers. In fact, about 10% of people with SAD get it “in reverse”. In fact, in countries that are near the equator, summer SAD is more prevalent. Experts aren’t sure why, but the longer days, and increasing heat and humidity may play a role. As with winter SAD, symptoms of summer depression often include loss of appetite, trouble sleeping, depression, weight loss, and anxiety.

The information provided is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Seek the advice of a doctor with any questions you may have regarding a medical condition. Never delay seeking or disregard professional medical advice because of something you have read here.