Seasonal affective disorder (SAD) — also known as seasonal depression and sometimes referred to as winter depression — is a type of depression that follows a seasonal pattern.
Typically, symptoms present during the fall and winter months when daylight hours grow shorter and the weather becomes colder and gloomier. A rarer form of SAD has the opposite pattern, with symptoms beginning in the spring or summer and resolving in the fall or winter. SAD is thought to be more prevalent in women, young people, people with bipolar disorder, and people who live further from the equator.
According to the Canadian Mental Health Association (CMHA), approximately 2 to 3 percent of Canadians will experience SAD in their lifetime. A further 15 percent will experience a less severe form of SAD that leaves them slightly depressed, but still able to go about their daily lives without major disruptions. While SAD is not unique to Canada, its prevalence and impact are notable in a country that is familiar with long, dark winters. Canadians living in more northern regions see even fewer daylight hours in the winter months, which may heighten the risk of seasonal affective disorder.
Like other forms of depression, SAD can interfere with a person’s sleep pattern and sleep quality. For those dealing with seasonal affective disorder, a number of approaches can be taken to alleviate symptoms and mitigate the effects of SAD on sleep.
What are the symptoms of seasonal affective disorder (SAD)?
Unlike non-seasonal depression, which can occur at any time of year, SAD symptoms usually begin in the late fall or early winter and subside in the spring or summer. Common symptoms of seasonal affective disorder include:
- Persistent feelings of sadness that remain for most of the day, nearly every day
- Difficulty concentrating
- Changes in weight or appetite (especially cravings for high-carbohydrate foods)
- Lack of energy or feelings of sluggishness
- Social withdrawal and loss of interest in activities you would usually enjoy
- Sleep disturbances, such as insomnia and excessive daytime sleepiness
Seasonal affective disorder and its associated symptoms can have a significant impact on a person’s daily functioning, affecting work, relationships, and overall quality of life.
How does seasonal affective disorder (SAD) affect sleep?
Reduced exposure to natural sunlight is understood to be a key trigger for seasonal affective disorder. It is believed that the lack of light during the fall and winter months can disrupt the body's internal clock (circadian rhythm) and affect the production of important sleep-related neurotransmitters like serotonin and melatonin.
Serotonin promotes wakefulness, while melatonin — which is released in response to the external cue of darkness — prepares the body for sleep. In SAD, delayed circadian timing is thought to present as early onset insomnia and morning hypersomnolence (difficulty falling asleep and difficulty waking up the following morning).
A 2016 study examining sleep problems during seasonal affective disorder found that participants with symptoms of SAD had a significantly increased risk of experiencing nightmares and insomnia. Around 16 percent of participants with SAD symptoms regularly had nightmares (compared to about 2 percent of those without symptoms), and 25 percent reported frequent insomnia, which affected approximately 8 percent of the group with no SAD symptoms. Individuals with symptoms of SAD were also noted to have short or long sleeping times more often than participants who did not have signs of seasonal affective disorder.
People with SAD might have trouble falling asleep or getting a good night’s sleep. They may also experience excessive daytime sleepiness, which can make it difficult to carry out daily tasks.
Managing and treating seasonal affective disorder (SAD)
Various treatments and strategies are available to help people who experience seasonal affective disorder. Light therapy — also known as phototherapy — involves exposure to an artificial light that mimics natural sunlight. The lightbox is used for a specified period of time each day (usually in the morning for around half an hour). As an effective, accessible, and non-invasive approach, light therapy is often used as the first-line treatment for SAD. An analysis of randomized controlled trials exploring the efficacy of light therapy in treating mood disorders found the treatment to be associated with a significant reduction in depression symptom severity in those with SAD.
Cognitive-behavioural therapy (CBT) and other forms of psychotherapy are also used in the treatment of seasonal affective disorder to help individuals identify negative thought patterns and develop coping techniques. In some cases, antidepressant medications may be prescribed to ease symptoms of SAD.
Maximizing exposure to natural sunlight throughout the day may help regulate circadian rhythms, and has also been shown to improve mood. Being outdoors, opening curtains around the home in the morning after awakening, and arranging workspaces near a window can help boost time spent in natural sunlight during the fall and winter months.
Many symptoms of seasonal affective disorder — such as lethargy, persistent feelings of sadness, and loss of interest in social activities — are shared with other types of depression. If you are experiencing symptoms of SAD that are affecting your daily life, it’s important to consult with a doctor, who can help rule out any other causes for your symptoms and establish a plan for treatment.