What is Seasonal Depression?

As the weather gets colder and days become shorter, you may notice you have less energy, feel a little less optimistic and spend more time alone. While this may not be a cause for concern, about 5% of the U.S population experience seasonal depression during the fall and winter months.  

Seasonal depression, or seasonal affective disorder (SAD), is a subtype of depression that begins and ends around the same time every year. This recurrent pattern generally begins in the fall or early winter months and ends around springtime, lasting about four to five months per year. This is known as winter-pattern SAD or winter depression. For people in the United States, the most difficult months tend to be January and February. 

Many people get a mild version of SAD known as the “winter blues.” As much as 20% of the population may get the winter blues, which is usually linked to something specific, such as holiday stress or grief over missing loved ones. The winter blues isn’t a medical diagnosis and usually goes away on its own after a few weeks or months. 

Some people might have depressive episodes during the spring and summer. This is known as summer-pattern SAD or summer depression, which affects about 10% of the population.  

What causes seasonal depression? 

Although the exact cause of SAD is unknown, it has been linked to a chemical imbalance in the brain prompted by shorter daylight hours and less sunlight in the wintertime. The main theory is that the lack of sunlight stops the hypothalamus from working properly. The hypothalamus is the part of the brain that maintains your body’s internal balance, called homeostasis. It does this by stimulating or inhibiting many of the body’s essential processes, including sleep cycles and production of substances that influence the pituitary gland to release hormones.  

Circadian rhythmThe lack of sunlight during the wintertime can lead to an overproduction of melatonin, a hormone released by the pineal gland at night that helps your body maintain its sleep-wake cycle. When you wake up in the morning, your body’s melatonin secretion drops off because light prompts the pineal gland to stop releasing the hormone. At night, darkness prompts the pineal gland to produce melatonin, making you feel sleepy and ready for bed. The increase in darkness and decrease in daylight during the winter can cause the pineal gland to overproduce melatonin. Too much melatonin can cause you to feel more tired and have less energy than usual. 

People with SAD also have trouble regulating serotonin, a brain chemical responsible for balancing mood. In one study, people with SAD had 5% more serotonin reuptake transporter (SERT) in the winter months than in the summer. SERT transports serotonin from the synaptic cleft to the presynaptic neuron. The synaptic cleft is a space that separates two neurons (the post- and pre-synaptic neurons) that helps nerve impulses pass from one neuron to the other. Higher levels of SERT lead to lower serotonin activity, causing depression. During the summertime, sunlight usually keeps SERT levels low, but when sunlight decreases in the fall and winter, there is a corresponding decrease in serotonin activity.  

When a decrease in serotonin and an increase in melatonin are combined, it can disrupt circadian rhythms. Circadian rhythms are 24-hour cycles that are part of the body’s internal clock. They respond primarily to light and dark and are connected to a “master clock” located in the suprachiasmatic nucleus within the hypothalamus.  

Wintertime also means less outdoor exposure to sunlight on the skin. People with SAD may produce less vitamin D, which is believed to play a role in serotonin activity. Both vitamin D deficiency and sufficiency have been associated with clinically significant depressive symptoms, but causal links between serotonin, melatonin, vitamin D, circadian rhythms, and SAD have not been confirmed.  

What are the symptoms of seasonal depression? 

People with SAD experience mood changes and symptoms similar to those of depression. The symptoms can range from mild to severe. 

Symptoms can include: 

  • Feeling depressed most of the day, almost every day 
  • Losing interest or pleasure in activities you once enjoyed 
  • Changes in appetite or weight  
  • Change in sleep; usually sleeping too much 
  • Loss of energy or increased fatigue despite increased sleep hours 
  • Increase in purposeless physical activity or slowed movements or speech  
  • Feeling worthless or guilty 
  • Difficulty thinking, concentrating, or making decisions 
  • Thoughts of death or suicide 

Winter-pattern SAD has additional symptoms, including:  

  • Oversleeping (hypersomnia) 
  • Overeating  
  • Weight gain 
  • Social withdrawal 
  • Low energy 

Summer-pattern SAD also has unique symptoms, including: 

  • Trouble sleeping (insomnia) 
  • Agitation and restlessness 
  • Poor appetite leading to weight loss 
  • Anxiety 
  • Episodes of violent behavior 

The key to receiving an accurate diagnosis of SAD is recognizing the recurrent pattern. Some people with SAD may start to experience a “slump” as early as August, while others won’t notice any symptoms until January. Generally, people with SAD don’t start to feel “normal” until May. 

To meet the DSM-5 diagnostic criteria for major depressive disorder with seasonal pattern, depression must be present during a specific season every year with full remittance during other seasons for at least two years, and with more seasons of depression than seasons without depression over a lifetime. While you won’t get a diagnosis of seasonal affective disorder the first time you experience symptoms, it’s important to pay attention to and track the pattern.  

Who is at risk for seasonal depression? 

Although anyone can get seasonal depression, women are four times more likely than men to get winter-pattern SAD. People who live further from the equator are also more likely to get SAD than people who live closer to the equator. Someone who lives in a northern state would be more likely to get SAD than someone who lives in a southern state. 

If you have a family history of winter pattern SAD, you are more likely to develop it yourself. You are also more likely to get winter pattern SAD if you have depression or bipolar disorder. 

How to manage seasonal depression 

If you have seasonal depression, there are a few ways you can manage your symptoms.  

Light therapy 

Since light plays such a primary role in seasonal depression, one treatment that can help is light therapy. It is often the first treatment recommended for SAD and is meant to replace the missing daylight hours with an artificial substitute. These lights are about 20 times brighter than regular indoor lights and filter out potentially damaging UV light.  

Light therapy lampDuring light therapy, patients will sit near a device called a light therapy box or lamp that gives off a light that mimics outdoor light. Patients sit in front of the light box every morning for 30 minutes or more, usually first thing in the morning after waking up. You may use it for up to two hours per day depending on the intensity of the light and how long you have been using light therapy. The light should reach your eyes, but do not stare directly at the light box. 

Light therapy is thought to affect brain chemicals that are linked to mood and sleep such as melatonin and serotonin. Light boxes are safe, effective, and available to buy without a prescription, although your doctor may recommend a specific box. The most common side effects of light therapy are headache, eye strain, and nausea. You might be more tired than usual during your first week of light therapy because it is changing your sleep-wake patterns, but the tiredness should start to improve in the second week.  

Studies have shown that light therapy can relieve SAD symptoms for as much as 70% of patients after a few weeks of treatment, but some patients may experience improvements sooner. Light therapy should be used every day into the spring when symptoms begin to go away on their own, but some people may stop using it after a few weeks once their symptoms start to improve.  

Sun exposure 

Sunlight is the main source of vitamin D, which can help with managing the symptoms of SAD. Although there isn’t as much sunlight during the fall and winter as there is during the spring and summer, it is still possible to get some sun exposure. Weather permitting, you can spend time outdoors or arrange your home or office so that you can get some sunlight through a window during the daytime.  

Although low levels of vitamin D have been found in patients with SAD, it is unclear if vitamin D supplementation can help relieve the symptoms. Make sure to consult with your doctor before starting a vitamin D supplementation.  


Since SAD is a type of depression that is associated with disruptions in serotonin activity, antidepressants called selective serotonin reuptake inhibitors (SSRIs) can be used to treat the symptoms. SSRIs increase the levels of serotonin in the brain and block the absorption (reuptake) of the chemical into neurons. Another type of antidepressant that may be prescribed for SAD is bupropion. It works by inhibiting the reuptake of dopamine, norepinephrine, and serotonin.  


Also known as talk therapy, psychotherapy is a general term for treating mental health problems by working with a mental health professional, such as a psychiatrist or psychologist. It can be used alone or in conjunction with medications or other treatments.  

Cognitive behavioral therapy (CBT) is an evidence-based psychological treatment that has been demonstrated to be effective for a range of problems, such as depression, anxiety, and substance use. Research studies have shown that CBT can lead to significant improvements in functioning and quality of life. Advances in CBT have been made based on research and clinical practice, and there is ample evidence that CBT methods can produce change.  

A form of CBT that has been adapted for people with SAD, known as CBT-SAD, relies on the basic techniques of CBT and focuses on helping patients replace negative thoughts about winter with positive thoughts. CBT-SAD also uses behavioral activation to help patients identify and schedule pleasant indoor or outdoor activities to cope with the wintertime.  

Talk to your doctor about which treatment or combination of treatments will work best for you. It usually takes at least four weeks to start seeing improvements, so don’t get discouraged if you don’t experience improvements right away. If you start feeling worse or experience any side effects, be sure to consult with your doctor. 

Get the support you need 

If you are struggling with seasonal depression, know that you’re not alone. At PatientsLikeMe, there are over 17,000 members who are also living with SAD. Join them today to learn how they are managing their symptoms and  get the support you need. 

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