Seasonal Depression In The Winter: What Is It And How Can You Treat It?

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

What is seasonal depression?

Seasonal affective disorder (SAD), commonly referred to as seasonal depression, is a form of major depressive disorder (MDD). The condition is more specifically termed major depression with seasonal pattern. If you are diagnosed with this disorder, you may experience cyclical depressive periods, with episodes often occurring in the winter or autumn and disappearing in spring and summer. 

What are the symptoms of seasonal depression?

To be diagnosed with seasonal depression, you must experience depressive episodes that occur around the same time each year for at least two consecutive years. You must also experience a full recovery of your symptoms after a period of depression. 

Symptoms of SAD are unique to the individual and vary widely. Common symptoms include:

  • Low mood 

  • Feelings of worthlessness

  • Increased appetite, particularly craving carbohydrate-dense foods

  • Weight increases

  • Hypersomnia and lethargy

  • Libido reductions

  • Irritability and anxiety (more common in spring-onset SAD)

If you are experiencing any of the above symptoms, but to a lesser degree, you may have subsyndromal SAD or the “winter blues.” This condition is more common but less severe than SAD itself. 

What causes winter seasonal depression?

Although seasonal depression has been widely researched, its exact cause is unknown. However, as seasonal depression tends to occur in the winter months, many medical experts have pointed to diminished sunlight as a trigger for depressive episodes. 

Less sunlight

Shorter days and cooler weather tend to reduce the amount of sun and UV light exposure you get during winter. This means your body cannot efficiently create vitamin D, resulting in lower levels in the body during the winter. 

Lower vitamin D levels

Reduced vitamin D levels may play a role in causing SAD. This is because vitamin D can directly affect mood through its interactions with important mood regulators like hormones and neurotransmitters. 

Lower vitamin D levels in the winter could account for the imbalance of serotonin common in individuals with SAD¹.

Low vitamin D serum levels² have also been shown to worsen depressive symptoms in some cases.

Lower serotonin levels

Serotonin is a mood-regulating neurotransmitter that requires vitamin D for its creation. According to the serotonin hypothesis, lower serotonin levels in the brain may increase the likelihood of developing types of depression, including SAD. 

Researchers have found that individuals with SAD have lower levels of serotonin¹.  

Increased melatonin

Another possible cause is increased production of melatonin during winter. Melatonin is a hormone that makes you feel sleepy.

Melatonin production is prompted by darkness, so the shorter days and longer nights in winter can increase melatonin production.

Melatonin is key to the phase-shift hypothesis³ of SAD. This hypothesis states that mood disorders, including SAD, may be based upon shifts in the usual sleep-wake circadian cycle.

A study⁴ found that individuals with SAD have differing onset and offset of melatonin secretion in the winter than in the summer. This melatonin secretion irregularity may result in sleep-related symptoms of SAD.

While melatonin has been shown to increase lethargy and hypersomnia, it is unlikely to account for all the complexities associated with SAD.


Seasonal depression in the winter can be very harmful if left untreated, so it is important to understand the treatment options available. Below are a few of the most researched treatments.

Light therapy

As low light exposure may cause SAD, light therapy could help.

Light therapy uses light boxes, which are small machines that emit either broad-spectrum or UV light. This form of therapy is often the first choice for treating SAD.

The treatment involves sitting in front of the lightbox for about 20-40 minutes a day, usually in the morning.

Using lightboxes in the morning helps regulate your circadian rhythm, which can improve your mood and sleep-wake cycles.

Studies have shown that regular light therapy with a broad-spectrum light at 10,000 lux for 30 minutes a day has a positive impact⁵ on serotonin and melatonin levels.

UV light boxes that are not broad-spectrum may also help with vitamin D synthesis. However, it is highly recommended to use broad-spectrum lightboxes along with a separate vitamin D supplement, as this minimizes any harmful effects of direct UV exposure.

Light therapy has been widely and safely used for years and has been highly effective in treating SAD. Some experts⁶ suggest this success is due to improvements in the sleep-wake cycle.

A study⁷ showed noticeable reductions in sleep disturbance and improvements in quality of life with the administration of light therapy, while another study⁸ found that these improvements occurred immediately, after only 20 minutes of light therapy treatment.

Light therapy has even been proven⁹ effective in treating SAD in children and young adults.

In addition to being highly effective, lightboxes are also readily available, affordable, and can be used throughout the year.

It is important to note that even though light therapy is considered safe with few to no side effects, it is not a suitable treatment for everyone. If you use photosensitizing medications, such as lithium, certain antibiotics, or antipsychotics, you should not use UV light therapy as these medications make the skin especially sensitive to the sun and can result in skin damage.

Speak to your doctor to find out whether light therapy is right for you.


Antidepressants may help you manage SAD symptoms if your symptoms are caused by serotonin dysregulation.

Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), aim to balance the serotonin system and ease depressive symptoms.

One study¹⁰ suggested that SSRIs (specifically, fluoxetine) can be as effective as light therapy for treating SAD. Both types of treatment were highly tolerable by patients, but SSRIs were considered slightly easier to use.

The specific SSRI sertraline has also been used to treat SAD. Patients who used sertraline reported¹¹ only mild side effects and significant reductions in their symptoms compared to taking a placebo.

Other medical experts have suggested that the antidepressant bupropion¹² could prevent SAD episodes from occurring if taken while people are in their recovery season. The benefit of this treatment is that you don’t need to wait until your symptoms get worse to start taking antidepressants. Instead, you could take bupropion preemptively and prevent future winter SAD episodes altogether.

Antidepressants are even more effective when combined with other treatments such as light therapy. One study¹³ indicated that taking citalopram in conjunction with one week of light therapy was sufficient to prevent relapse in SAD patients.

Cognitive behavioral therapy

Cognitive behavioral therapy (CBT) is a common treatment for depression that helps you to identify and change unhelpful negative thoughts and learned behaviors that underpin depressive symptoms. CBT has been effective in treating many depressive disorders, including SAD.

One study¹⁴, in particular, found that engaging in CBT twice a week for six weeks was as effective as daily light therapy. The severity of depressive symptoms decreased significantly with both forms of treatment.

Another study¹⁵ exploring SAD treatment suggests that patients receiving CBT or a combination of CBT and light therapy experience less severe symptoms in the subsequent winter than those just receiving light therapy. This indicates that there is a psychological component of SAD symptoms which CBT can help to resolve.

CBT also tends to have longer-lasting¹⁶ effects than other forms of treatment because it targets the root cause of the symptoms instead of just the symptoms themselves.


Exercise is a useful supplementary treatment for depressive disorders, including SAD. To improve your mood and ease your symptoms, it is recommended that you begin a regular exercise program.

Some experts¹⁷ even suggest that exercise’s antidepressant effects are comparable to bright light treatment for people living with SAD. Exercise can result in significant improvements in mood and reduce other symptoms, such as feeling lethargic.

A recent systematic review¹⁸ suggested that just 10 to 30 minutes of exercise can ease depressive symptoms or even prevent them from occurring altogether. Moderate intensity exercise was shown to have the most significant effect, but any movement is beneficial.

The antidepressant effect of exercise is even more significant if combined with light therapy.

One study¹⁹ suggests that patients who exercise in bright light conditions experience large improvements in mood and a reduction in their depressive symptoms, increasing their quality of life.

When should I seek help?

While it is natural to feel sad, especially in the colder, darker winter months, if you find that your feelings significantly affect your quality of life, it may be time to seek help.

If you are experiencing more frequent depressive episodes that are increasing in severity or are without an obvious cause, you should speak to your doctor.

If you or someone around you is experiencing suicidal ideation or behavior, or self-harm, you should seek immediate help by contacting emergency services or a suicide helpline.

The lowdown

Seasonal affective disorder in the winter is a relatively common mental health disorder that can negatively impact your quality of life. Many symptoms vary according to the individual, so if you recognize any of the above symptoms in yourself or others, it is recommended that you seek help.

Available treatments include light therapy, antidepressants, cognitive behavioral therapy, and regular exercise.

As with any depressive disorder, it is important to remember that you are not alone. There are many possible treatments for SAD which may allow you to lead a more pleasurable and fulfilling life if you seek the right support. Make sure you contact your doctor for a diagnosis and treatment plan.

  1. Seasonal difference in brain serotonin transporter binding predicts symptom severity in patients with seasonal affective disorder (2016)

  2. Effect of vitamin D supplement on depression scores in people with low levels of serum 25-hydroxyvitamin D: nested case—control study and randomised clinical trial | Cambridge University Press

  3. The circadian basis of winter depression (2006)

  4. A circadian signal of change of season in patients with seasonal affective disorder (2001)

  5. Light therapy and serotonin transporter binding in the anterior cingulate and prefrontal cortex (2016)

  6. Morning vs evening light treatment of patients with winter depression (1998)

  7. Improvement in fatigue, sleepiness, and health-related quality of life with bright light treatment in persons with seasonal affective disorder and subsyndromal SAD (2011)

  8. Short exposure to light treatment improves depression scores in patients with seasonal affective disorder: A brief report (2010)

  9. A controlled trial of light therapy for the treatment of pediatric seasonal affective disorder (1997)

  10. Seasonal affective disorder: An overview of assessment and treatment approaches (2015)

  11. A placebo-controlled study of sertraline in the treatment of outpatients with seasonal affective disorder (2004)

  12. Seasonal affective disorder and its prevention by anticipatory treatment with bupropion XL (2005)

  13. Relapse prevention by citalopram in SAD patients responding to 1 week of light therapy. A placebo-controlled study (2004)

  14. Randomized trial of cognitive-behavioral therapy vs. light therapy for seasonal affective disorder: Acute outcomes (2021)

  15. Cognitive predictors and moderators of winter depression treatment outcomes in cognitive-behavioral therapy vs. light therapy (2013)

  16. Outcomes one and two winters following cognitive-behavioral therapy or light therapy for seasonal affective disorder (2015)

  17. Mood and energy regulation in seasonal and non-seasonal depression before and after midday treatment with physical exercise or bright light (2000)

  18. Special issue – therapeutic benefits of physical activity for mood: A systematic review on the effects of exercise intensity, duration, and modality (2018)

  19. Bright-light exposure combined with physical exercise elevates mood (2002)

Other sources:

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