Seasonal affective disorder (SAD) - Symptoms & causes

Jul 13, 20249 min
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Clinical Psychologist
girl having seasonal depression

Have you ever heard of the term ‘winter blues’? Or have you heard people saying ‘I am feeling blue’?

When people are going through a difficult time in their life, especially a low period, they refer to this experience as feeling blue. 

Fun Fact:

The phrase "feeling blue" has nautical origins dating back to the 17th century. When a ship lost its captain or an officer during a voyage, the crew would fly blue flags and paint a blue band along the ship's hull when returning to port. The color blue came to symbolize mourning and sadness.

The association of the color blue with melancholy also has roots in ancient Greek mythology.  Over time, this association with the colour blue and sadness became ingrained in Western culture, leading to the modern expression "feeling blue" to describe a state of melancholy or sadness.

At times, feeling depressed can be a result of seasonal changes. We see shifts in patterns of behaviour across species linked with changes in the season, such as many animals experience hibernation during the winter season, where they slow down their heart rates, and sleep in.

Human beings, too, naturally go through shifts in mood, energy, and lifestyle with seasonal changes. Have you experienced the feeling of not wanting to get out of your blanket in the winter months for hours? Thus, the usage of the term ‘winter blues’. Winters are generally a time when the body feels slow due to the external environment. 

However, when these seasonal changes begin impacting daily life and functionality, specifically making one feel low throughout the day for consecutive months, this is what is called Seasonal Affective Disorder (SAD).

About 3% of the people worldwide are impacted by SAD. SAD is a mood disorder in which people experience a shift in their mood states, especially feeling low during the winter months of the season.

Seasonal Depression - SAD (Seasonal Affective Disorder)

SAD is a form of depression that typically interferes with day-to-day living. The disorder is significantly associated with a lack of presence of sunlight in the environment that impacts our internal body clock.  Here are some common symptoms associated with SAD:

  • Depressed or low mood

This period is characterized by feeling sad typically with the onset of the winter season and the absence of any other specific trigger such as the loss of a job.   

  • Shifts in Appetite

While a person experiencing depression may experience fluctuations in hunger levels, sometimes feeling more hungry and in some episodes losing their appetite completely, with winter-onset SAD, people typically experience an increased desire to eat specific foods higher in caloric intake. 

  • Sleep Disturbances

The onset of depression usually comes with variations in the sleep cycle, people experiencing seasonal depression typically see an increased need for sleep, not feel like coming out of bed. 

  • Fatigue

It is common to experience feeling tired despite the longer hours of sleep, almost as if the body hasn’t felt rested. 

  • Feelings of disinterest

With feeling low, comes feeling a lack of interest in doing most activities that at one point proved to make one feel happy. This can range from simpler exercises such as no longer feeling interested in eating chocolates to more complex interests such as no longer wanting to play tennis. 

  • Attention

People experiencing SAD may also experience difficulty in sustaining attention to tasks. This can range from concentrating on everyday tasks such as folding clothes to complex tasks such as completing a work deadline. This may include easy forgetfulness and difficulty in making decisions as well. 

  • Overwhelm with Heavier Emotions

In the range of experiencing low mood, people experiencing SAD typically experience heavy feelings of hopelessness, helplessness, and worthlessness. This includes feelings of hopelessness towards the future, feeling helpless in terms of nobody being able to help them in their struggles, worthless in terms of experiencing low self-esteem. It is often accompanied by irritability that is not resolved with the situation change.

  • Suicidal Thoughts

The heaviness of low mood may come with thoughts about ending life, which in the case of SAD are often seen as the season shifts for the year. 

It is important to note that not everyone would experience all these symptoms, however, to meet the diagnosis of SAD one should experience the symptoms for a length of a few months (typically 4-6 months) consecutively for two years. 

Types of Seasonal Affective Disorder (SAD)

There are majorly two forms of this disorder based on the seasonal patterns of the year. Following is a brief description of the same: 

Fall Onset SAD

Fall onset SAD is also referred to as winter depression, in which people typically experience symptoms such as:

  •  Increase in appetite (particularly eating more carbohydrates)
  • Social withdrawal
  • Increased need for sleep

The winter depression is also the most common type of SAD. For most people, this would begin around the time of November and last until February. 

Spring Onset SAD

Spring Onset SAD is also referred to as summer depression, in which people experience symptoms such as:

  •  Loss of appetite often leads to weight loss
  • Disturbances in sleep (often experiencing insomnia/ lack of sleep)
  • Agitation and restlessness in their body
  • Racing thoughts

This is a less common type of SAD.

Understanding Why SAD occurs?

Researchers are still attempting to understand why SAD occurs, with more cases of fall onset SAD or winter depression being available, it is difficult to conclusively say what might begin this cycle of feeling low a few months of the year annually. Here are a few reasons which might cause SAD to occur:

  1. Disturbance in Circadian Rhythms

The body's internal clock, known as the circadian rhythm, regulates sleep-wake cycles. Nature’s light and darkness influence this internal clock. During the shorter days of fall and winter, the reduced exposure to sunlight can disrupt the circadian rhythm, leading to feelings of fatigue, difficulty waking up, and overall mood disturbances.

  1. Impact on Mood-Regulating Neurotransmitters

Sunlight exposure is crucial for the production of certain chemicals in the brain that regulate mood. One of the primary chemicals impacted by sunlight is called serotonin. Lower levels of sunlight can lead to decreased serotonin production, which is associated with feelings of depression and anxiety. Serotonin levels are naturally higher during the brighter months of spring and summer, contributing to a more stable mood.

  1. Changes in Sleep Patterns

It is often noted that people experiencing SAD have disturbances in their Melatonin levels. Melatonin is a hormone that helps regulate sleep. For people with winter-pattern SAD, the body may produce melatonin in larger quantities, increasing the need for sleep. For people with summer-pattern SAD, the body may produce melatonin in lowered quantities, causing disruptions in sleep patterns. 

These sleep disturbances can be a direct result of more/less sunlight present in the environment too as melatonin levels in the body are influenced by the same.

  1. Vitamin D Deficiency

Less sunlight can lead to lower levels of vitamin D, which is linked to serotonin production and can contribute to depressive symptoms. Staying indoors during the winter season also means less exposure to sunlight which can contribute to low mood. However, it is important to note that it is not a direct cause contributing to the development of SAD. 

Risk Factors 

Risk factors are characteristics or conditions that increase the likelihood of developing a mental health condition. Here are a few risk factors associated with SAD:

Genetic Factors

Some individuals may have a genetic predisposition to SAD, making them more susceptible to the disorder. SAD is more common in people with depression or bipolar disorder, especially bipolar II disorder, which involves repeated depressive episodes and hypomanic episodes (less severe than the typical manic episodes of bipolar I disorder). If there is a family history of experiencing mood disorder, it increases the chances of experiencing low mood with seasonal change.

Geographical Location

People living far from the equator are more likely to experience SAD due to more significant seasonal variations in daylight. This includes countries such as Sweden, Finland, and many other Nordic countries, especially prone to experiencing winter-pattern depression. However, interestingly enough these are also countries that rank highest on the world happiness index year after year. Read more about this paradox here


The following four types of treatment options are available when it comes to SAD. These are often used in combination with one another. 

Light Therapy 

For people experiencing winter pattern depression, light therapy is a go-to choice. Sunlight is one of the main causes of experiencing SAD and typically in the winter seasons people experience less sunlight. With light therapy, a person sits in front of a light box with typically a power of 10,000 lux everyday first thing in the morning for typically half an hour. This is a way in which we expose the body to light mimicking sunlight minus the Ultraviolet rays. It is proven to be beneficial for people experiencing SAD but can have side effects for people with certain eye diseases. It is important to check with your healthcare provider before implementing any tools of treatment. 


Medications used to treat depression, known as antidepressants, can be effective for SAD either alone or in combination with talk therapy. Antidepressants function by altering the brain's production or use of certain chemicals involved in mood and stress regulation. Since SAD, like other forms of depression, is linked to serotonin activity disruptions, selective serotonin reuptake inhibitors (SSRIs) are sometimes prescribed to alleviate symptoms. These medications can greatly improve mood.


Psychotherapy or talk therapy could also be used for people experiencing low mood, teaching them alternate ways of thinking and managing the condition.

Cognitive Behavioural Therapy (CBT) is a type of therapy often proven to treat depression. A specific type of Cognitive Behavioural Therapy known as CBT-SAD, is specifically developed for treating Seasonal Affective Disorder. CBT-SAD typically consists of two weekly group sessions over a span of six weeks, aimed at replacing negative seasonal thoughts, such as those about winter darkness or summer heat, with more positive ones. Additionally, CBT-SAD incorporates behavioral activation, a process that helps individuals identify and plan enjoyable indoor or outdoor activities to counteract the usual loss of interest experienced during winter or summer.

Vitamin D supplementation

Low levels of Vitamin D in the body are linked with the development of SAD. One course of treatment often includes checking for deficiencies in the body with regular blood work and providing vitamin D supplements to elevate the overall levels in the body.


Once diagnosed with SAD, it becomes easier to track mood dips as season changes are one of the biggest predictors of the same. It is essential to keep the following in mind to manage this condition in a better way: 

  • Keeping a mood diary: Tracking your mood shifts can help you feel more in control of the situation. 
  • Regulating Sleep-wake cycle: It is important to not let seasonal changes shift sleep cycles especially if you are diagnosed with SAD. Sleeping and waking up on the same time, specifically when the body is going through the cycle of low mood is a crucial step in management.
  • Movement: Moving your body is directly linked to producing more happier mood. Even if going outside, during winter, is difficult, putting on your favourite music and dancing for a few minutes can help in managing your overall mood.

In conclusion, SAD is a form of depression and is influenced by seasonal change, with more people impacted by the winter depression. It is more intense than one experiencing the ‘winter blues’ as the low mood impacts the overall functionality and the symptoms last for 4-6 months every year. In addition to low mood, a person may experience, fatigue, disturbances in sleep and appetite, feelings of social withdrawal, or restlessness. While there can be several internal factors contributing to the development of the disorder, one major cause is the sunlight in the environment. There are various treatment options available today to help manage this disorder. Information about continuous ways of dealing with the condition is essential as this can be an annual occurrence for many people. 


Does vitamin D help with Seasonal Affective Disorder?

Yes, vitamin D can help with Seasonal Affective Disorder (SAD). Some studies suggest that vitamin D supplementation may alleviate symptoms of SAD, as the disorder is often linked to reduced sunlight exposure, which can lead to vitamin D deficiency. However, more research is needed to confirm its effectiveness. It's important to consult a healthcare provider for personalized advice.

Can Seasonal Affective Disorder cause anxiety?

Yes, Seasonal Affective Disorder (SAD) can cause anxiety. People with SAD often experience increased levels of anxiety during the specific seasons when their symptoms worsen, typically in winter. This anxiety can manifest as general nervousness, worry, or panic attacks. Treatment for SAD, including light therapy, antidepressants, and cognitive-behavioral therapy, can help manage both depression and anxiety symptoms.

Can Seasonal Affective Disorder cause autism?

No, Seasonal Affective Disorder (SAD) cannot cause autism. Autism is a neurodevelopmental disorder that typically manifests in early childhood, whereas SAD is a type of depression related to seasonal changes, most commonly occurring in adulthood. While both conditions can co-occur, one does not cause the other. If you have concerns about autism, it's best to consult with a healthcare professional for appropriate evaluation and guidance.


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National Institute of Mental Health. (n.d.). Seasonal Affective Disorder. Retrieved from 

Pjrek E, Baldinger-Melich P, Spies M, Papageorgiou K, Kasper S, Winkler D. Epidemiology and socioeconomic impact of seasonal affective disorder in Austria. Eur Psychiatry. 2016 Feb;32:28-33. doi: 10.1016/j.eurpsy.2015.11.001. Epub 2016 Jan 21. PMID: 26802981.

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