What is seasonal affective disorder (SAD)?

Seasonal affective disorder (SAD) is depression that gets triggered by a change in seasons, usually when fall starts. This seasonal depression gets worse in the winter before ending in the spring.

Some people may get a mild version of SAD known as the “winter blues.” It’s normal to feel a little down during colder months. You may be stuck inside, and it gets dark early.

But full SAD goes beyond that — it’s a form of depression. Unlike the winter blues, SAD affects your daily life, including how you feel and think. Fortunately, treatment can help you get through this challenging time.

Can people get summer depression?

Some people get a rare form of SAD called “summer depression.” It starts in the late spring or early summer and ends in the fall.

How common is seasonal affective disorder (SAD)?

About 5% of adults in the United States experience SAD. It tends to start in young adulthood. SAD affects women more than men, though researchers aren’t sure why. About 75% of people who get seasonal affective disorder are women.

About 10% to 20% of people in America may get a milder form of the winter blues.

Who is at risk for seasonal affective disorder (SAD)?

SAD is more common in younger people and women. You’re also at higher risk if you:

  • Have another mood disorder, such as major depressive disorder or bipolar disorder.
  • Have relatives with other mental health conditions, such as depression or schizophrenia.
  • Live at high latitudes (farther north of the equator), such as Alaska or New England.
  • Live in cloudy regions.

People with seasonal affective disorder may also have other mental conditions, such as:

What causes seasonal affective disorder (SAD)?

Researchers don’t know exactly what causes seasonal depression. The lack of sunlight may trigger the condition in people who are prone to getting it. The theories suggest:

  • Biological clock change: When someone has less exposure to sunlight, their biological clock shifts. This internal clock regulates mood, sleep and hormones. When it changes, people may have trouble regulating their moods.
  • Brain chemical imbalance: Brain chemicals called neurotransmitters send communications between nerves. These chemicals include serotonin, which contributes to feelings of happiness. People at risk of SAD may already have less serotonin activity. Since sunlight helps regulate serotonin, the lack of winter sun can make the situation worse. Serotonin levels can fall further, leading to mood changes.
  • Vitamin D deficit: Serotonin also gets a boost from 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.
  • Melatonin boost: Melatonin is a chemical that affects sleep patterns. The lack of sunlight may stimulate an overproduction of melatonin in some people. They may feel sluggish and sleepy during the winter.
  • Negative thoughts: People with SAD often have stress, anxiety and negative thoughts about the winter. Researchers aren’t sure if these negative thoughts are a cause or effect of seasonal depression.

What are the symptoms of seasonal affective disorder (SAD)?

SAD is a type of depression, rather than a separate disorder. So people who have seasonal affective disorder may have signs of depression, including:

  • Sadness.
  • Anxiety.
  • Carbohydrate cravings and weight gain.
  • Extreme fatigue and lack of energy.
  • Feelings of hopelessness or worthlessness.
  • Inability to concentrate.
  • Irritability.
  • Limbs feeling heavy.
  • Loss of interest in usual activities, including withdrawing from social activities.
  • Sleeping more.
  • Thoughts of death or suicide.

People who have summer SAD may experience:

  • Agitation and restlessness.
  • Anxiety.
  • Decreased appetite and weight loss.
  • Episodes of violent behavior.
  • Trouble sleeping.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy