Picture of a woman looking out a window

The science behind seasonal depression — and how you can get ahead of it

Medically reviewed on November 4, 2022 by Morgan Spicer, Medical Communications Manager. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

With the clock set back and long days of summer transitioned to shorter and darker ones, it’s officially time to welcome in fall. For some, this changing of the seasons means not only farewell to pool days and summer cookouts until it’s time to meet again — but a significant impact on mood and energy level that’s more than just the winter blues.

Seasonal affective disorder, also known as SAD, is a form of depression that many people experience during the dark autumn and winter months.[1] According to the Diagnostic Manual of Mental Disorders (DSM-5), seasonal affective disorder is not a separate disorder but rather a subtype of depression characterized by its recurrent seasonal pattern.[2]

While it’s more common for symptoms of SAD to take place during the late fall and winter and last for about 4 to 5 months per year, some people may be affected by depressive episodes during the spring and summer months. This less-commonly occurring subtype is known as summer-pattern SAD, or summer depression.[1]

Who is more likely to experience SAD?

The Cleveland Clinic estimates that about 5% of adults in the U.S experience SAD, while about 10% to 20% of people in the United States may suffer from milder forms of the winter blues.[3] Researchers have also found that SAD occurs more often in women than in men and tends to show up in young adulthood, usually between the ages of 18 and 30.[3]

According to the National Institute of Mental Health, seasonal affective disorder has been linked to a biochemical imbalance in the brain caused by a lack of sunlight.[1] Because of this, SAD is more common in those who live further from the equator where winter means less hours of daylight.[1]

In addition to factors of geographic location, gender, and age, SAD also tends to be more common in people who experience major depressive disorder or bipolar disorder.[1] According to the National Institute of Mental Health, those who experience SAD may be more likely to have other mental disorders, such as attention-deficit/hyperactivity disorder, an eating disorder, an anxiety disorder, or panic disorder.[1] Research also points to a genetic correlation, since those with relatives who have SAD, or other forms of depression or mental health conditions — such as schizophrenia or major depression — are also more likely to experience SAD.[1]

What are the symptoms of SAD?

Because SAD is not a separate disorder but rather a type of depression, the signs and symptoms associated with SAD tend to be similar to those occurring in major depression.[1] According to the National National Institute of Mental Health, symptoms of major depression may include:

  • Feeling depressed most of the day, nearly every day
  • A loss of interest in activities you once enjoyed
  • Changes in appetite or weight
  • Problems sleeping
  • Feeling sluggish or agitated
  • Having low energy
  • Feeling hopeless or worthless
  • Having difficulty concentrating
  • Loss of libido
  • Having frequent thoughts of death or suicide

In addition to these symptoms, winter-pattern SAD may include these additional symptoms: oversleeping, social withdrawal, weight gain, oversleeping, and overeating — particularly a craving for carbohydrates.[1]

What causes SAD?

While it’s true that scientists do not fully understand what causes SAD, research suggests that people with SAD may have reduced activity of serotonin — the brain chemical (neurotransmitter) which helps regulate mood.

Other findings point to an overproduction of melatonin — a hormone integral maintaining the body’s sleep-wake cycle — as a cause of seasonal affective disorder.[1] In these instances, changes in levels of serotonin and melatonin can disrupt an individual's circadian rhythm, resulting in an inability to adapt to the seasonal changes, which then in turn leads to changes in sleep, mood, and behavior.[1]

A lack of vitamin D is also thought to play a role in seasonal depression. Because vitamin D is believed to promote serotonin activity, reduced exposure to sunlight and less time spent outdoors during the winter months means those with SAD may have lower vitamin D levels.[1] This may further hinder serotonin activity.[1]

How can you prevent or manage SAD?

To learn more about the ways in which seasonal affective disorder can be managed, we spoke with Dr. Adrian Aguilera, a clinical psychologist who specializes in treating depression and anxiety with cognitive and behavioral approaches. Below, Dr. Aguilera shares some tips on how to tackle SAD head-on this season.

How is seasonal affective disorder treated?

According to Dr. Aguilera, the primary treatment for SAD is light therapy.[4] This involves the use of exposure to a bright light, usually from a fluorescent light box, preferably in the morning for 30 minutes to 2 hours depending on how bright the light is. “Light is thought to work by prompting the body to suppress the release of melatonin which is typically activated in darkness,” Dr. Aguilera said. “Exposure to light can help compensate for the lack of natural light in the winter months which can contribute to SAD.”

In addition to light therapy, effective treatment may include cognitive behavioral therapy – which can help identify and change negative thoughts and behaviors that may be making you feel worse.[5] “When we feel depressed we tend to see the negative in most situations or see things in an unbalanced way that tilts toward the negative,” said Dr. Aguilera. “These thoughts typically make us feel worse and lessen our motivation to engage in the world. Making an effort to see the other side in a situation and to focus on what is going well or can go well can provide a spark of motivation that can be energizing.”

Dr. Aguilera said it’s also important to continue to engage in various forms of exercise and activities that we find meaningful and enjoyable, even as the days grow colder. During the darker and colder months, this may mean getting creative with ways to bring such active routines inside.

Additionally, some people with SAD may benefit from antidepressant treatment, especially if symptoms are severe.[5]

Are there ways SAD can be prevented?

According to Dr. Aguilera, efforts to prevent SAD start by becoming more aware of how darkness impacts us and taking the necessary steps to counteract its effects. “Things may be more difficult but it’s important to continue exercising, socializing, and engaging meaningfully in life despite the messages that darkness and cold may be telling our bodies,” Dr. Aguilera said.

Because the darker months coincide with the holidays which may mean travel and events that often revolve around food and drink, it can be tricky to navigate a balance. “We are learning more about ways in which the gut and brain are connected and how eating healthy, balanced meals can also give us energy and lift our spirits,” said Dr. Aguilera. “We can still engage but we want to do so mindfully.”

When it comes to keeping up with exercise, flexible thinking and creativity about how to maintain activeness are important. “Maybe it includes exercising at home or at a gym,” said Dr. Aguilera. “ But hey, why not go out dancing? Or take a brisk walk/run during the few hours of light? Make a plan and reward yourself for taking positive steps!”

How can someone best take care of themself if they suffer from SAD?

“It’s crucial to first start by being kind to ourselves and recognize that there are many factors that influence our mood and depression symptoms,” said Dr. Aguilera. In addition to practicing self-compassion, light therapy, and movement, it’s important to also take inventory of one's thought process and behaviors.

“The lack of light can sometimes give our bodies the message that it’s time to retreat inward and isolate,” said Dr. Aguilera. “Alone time can be helpful in moderation, but we also need to give our body what we know it needs to be healthy.”

If you are struggling with feelings of depression and need someone to talk to, you can get support by calling the National Suicide Prevention Lifelineat 988 or by texting HOME to 741-741, the Crisis Text Line.

References: 1. Seasonal Affective Disorder. National Institute of Mental Health. URL. Accessed October 24, 2022. 2. Seasonal Affective Disorder (SAD). American Psychiatric Association. URL. Accessed October 24, 2022. 3. Seasonal Depression (Seasonal Affective Disorder). Cleveland Clinic. URL. Accessed October 24, 2022. 4. How Should I Obtain a Light Box? Yale School of Medicine.URL. Accessed October 24, 2022. 5. Seasonal affective disorder (SAD). Mayo Clinic. URL. Accessed October 24, 2022.

Everlywell makes lab testing easy and convenient with at-home collection and digital results in days. Learn More