What Is Seasonal Affective Disorder (SAD)? Symptoms, Causes, Treatment, and Its Link to Bipolar Disorder

Every fall and winter, you may find yourself tiring easily. Getting out of bed in the morning is a struggle, and even a long night’s sleep doesn’t leave you rested. You may even lose motivation and want to stay home instead of seeing people.
 

Changes in daylight and the seasons can affect your mood. But if these changes are hard to ignore or start getting in the way of your work or daily life, they could be related to seasonal affective disorder (SAD).
 

In this article, you’ll learn:
 

• What seasonal affective disorder is
• Which symptoms to watch for
• What causes seasonal depression
• How to tell the winter blues from seasonal depression
• When winter lows and spring or summer highs may signal bipolar disorder

• How to manage seasonal depression

   

What Is Seasonal Affective Disorder?

Seasonal affective disorder (SAD) is also known as seasonal depression. Because symptoms usually appear in fall and winter and ease in spring and summer, it’s sometimes called winter depression.
 

SAD isn’t a standalone diagnosis. A psychiatrist first determines whether a person has major depressive disorder or bipolar disorder. They then evaluate whether the person’s mood episodes follow a regular seasonal pattern [1].
 

Even in subtropical Taiwan, where sunlight is relatively plentiful, seasonal changes can still affect mood. For example, a Taipei study published in 2025 found that about one in four patients with mood disorders experienced noticeable seasonal mood changes [4].
 

What Are the Common Symptoms of Seasonal Affective Disorder?

SAD typically involves the following main symptoms:
 

• Persistent low mood
• Loss of interest in everyday activities you used to enjoy
• Cravings for sweets or starchy foods, leading to weight gain
• Sleeping more than usual
• Low energy, fatigue, or lack of motivation
• Daytime sleepiness
   

In terms of symptoms alone, SAD looks a lot like other forms of depression. What sets it apart is whether episodes follow a regular seasonal pattern.
 

Does Seasonal Depression Only Happen in Fall and Winter?

Not always. For a small number of people, symptoms appear in spring or summer and gradually improve in fall and winter. This form is known as summer-pattern SAD.
 

A 2025 systematic review and meta-analysis of 24 studies involving 32,866 people estimated the prevalence of summer-pattern SAD at about 0.57% [6].
 

Unlike winter-pattern SAD, the summer pattern more often involves insomnia, poor appetite, weight loss, or agitation [2].
 

What Causes Seasonal Depression?

The exact cause of SAD is still unclear. One leading explanation is that reduced sunlight may affect how the hypothalamus works. This part of the brain helps regulate the body’s natural rhythms, and changes in its activity may affect the following [2]:

1.Internal body clock

Less sunlight may disrupt your circadian rhythm and shift the timing of sleep and wakefulness, leaving you feeling tired and down.
 

2.Neurotransmitters and hormones

Changes in daylight may affect serotonin activity and melatonin production, which can influence mood and sleep.
 

Research has also found that some people may be more likely to develop SAD. These include women, younger people, those living farther from the equator, and people with a family history of depression or bipolar disorder [1].
 

How Can You Tell the Winter Blues From Seasonal Depression?

When evaluating you, a psychiatrist will consider three factors [1]:
 

• Timing: Whether symptoms consistently start in a particular season and fully go away at another time of year.
• Episode history: Whether symptoms have appeared in the same season for two years in a row, with no similar episodes at other times of year. It also matters whether most past episodes have followed the seasons.
• Impact: Whether symptoms clearly affect your work, sleep, relationships, or daily life.
   

If your symptoms are affecting your life, it’s worth getting evaluated, even if they haven’t followed a seasonal pattern for two years. You can also track changes in your mood, sleep, and appetite and share them with your psychiatrist.
 

Low in Winter, Full of Energy in Spring and Summer? Watch for Signs of Bipolar Disorder

When they feel low in winter, many people think of depression first. But seasonal mood changes may also be linked to bipolar disorder [1].

Research suggests that bipolar disorder symptoms may also shift with the seasons. Depressive episodes tend to occur in early winter, while hypomania or mania more often appears in spring and summer [3][4].

Low moods in winter are usually easier to notice. But high energy and an elevated mood in spring and summer are sometimes mistaken for simply feeling better. As a result, possible signs of hypomania or mania may be overlooked.
 

If you often feel low in winter and have experienced any of the following at other times of year, be sure to tell your psychiatrist:

• Sleeping very little without feeling tired
• Having much more energy or being much more active
• Talking or thinking faster than usual
• Feeling far more confident
• Making shopping, investing, or other decisions more impulsively
   

This information can help your psychiatrist get a fuller picture of your condition and choose the right treatment.
 

How Can You Manage Seasonal Depression?

If your symptoms are mild, you can start with some lifestyle changes [2]:
 

• Get more sunlight: Spend time outdoors during the day when you can, such as taking a walk during your lunch break.
   
• Exercise regularly: Build exercise into your week. You can also take up hobbies that help you relax.
   
• Stick to a consistent schedule: Go to bed and wake up at about the same time each day so your body clock is less likely to get thrown off.
   
• Stay connected: Keep in touch with friends and family, and share how you’re feeling to help keep your mood steady.
   
• Keep a mood journal: Write down your mood and sleep each day to track changes. You can also share it with your psychiatrist.
   

If your symptoms are significantly affecting your life, it’s a good idea to seek professional help.
 

Common treatment options for seasonal depression include [1][2]:

• Light therapy: People with winter-pattern SAD can use a special light box, also called a SAD lamp. Treatment typically involves 30 to 45 minutes of 10,000-lux light each morning to help regulate the body’s rhythms. However, check with a professional before you start, especially if you have a history of bipolar disorder or an eye condition.
   
• Cognitive behavioral therapy (CBT): Working with a psychologist or psychiatrist, you learn to change how you see things and reduce the impact of negative thoughts on your mood.
   
• Antidepressants: Some people have had winter-pattern SAD several times. For them, research suggests that starting certain antidepressants early may help lower the risk of it coming back [7].
   

For people who meet the criteria for major depressive disorder, a psychiatrist may also consider rTMS (repetitive transcranial magnetic stimulation). rTMS may be an option if medication hasn’t worked well, its side effects are hard to tolerate, or there are other medical reasons to consider it. 
 

Final Thoughts

Your mood and energy may drop noticeably every fall and winter, even making work and daily life harder to manage. If so, that pattern is worth paying attention to.

When symptoms are mild, small changes to your daily habits are a good place to start.
 

If things don’t improve, or if you’ve had periods of unusually elevated mood and high energy, consider seeing a psychiatrist. Bring your mood journal so you can discuss the right approach together.
 

Author: Dr. Hung-Hsi Wu, MD

Specializes in:

Anxiety disorders, depression, autism/Asperger’s syndrome, attention-deficit/hyperactivity disorder, children and adolescent populations​​​​​​​​​​​​​​​​

Reference

[1] Melrose, S. (2015). Seasonal affective disorder: An overview of assessment and treatment approaches. Depression Research and Treatment, 2015, 178564. https://doi.org/10.1155/2015/178564

[2] National Institute of Mental Health. (2023). Seasonal affective disorder. National Institutes of Health. https://www.nimh.nih.gov/health/publications/seasonal-affective-disorder

[3] Geoffroy, P. A., Bellivier, F., Scott, J., & Etain, B. (2014). Seasonality and bipolar disorder: A systematic review, from admission rates to seasonality of symptoms. Journal of Affective Disorders, 168, 210–223. https://doi.org/10.1016/j.jad.2014.07.002

[4] Chang, C. E., Chen, H. C., Chen, I. M., et al. (2025). Evaluation of seasonal variations for the seasonal pattern assessment in mood disorder patients and healthy controls. BMC Psychiatry, 25, 458. https://doi.org/10.1186/s12888-025-06916-y

[5] Benedetti, F. (2018). Rate of switch from bipolar depression into mania after morning light therapy: A historical review. Psychiatry Research, 261, 351–356. https://doi.org/10.1016/j.psychres.2018.01.013

[6] Kim, K., et al. (2025). Global prevalence of seasonal affective disorder by latitude: A systematic review and meta-analysis. Journal of Affective Disorders, 390, 119807. https://doi.org/10.1016/j.jad.2025.119807

[7] Gartlehner, G., et al. (2019). Second-generation antidepressants for preventing seasonal affective disorder in adults. Cochrane Database of Systematic Reviews, CD011268. https://doi.org/10.1002/14651858.CD011268.pub3

[8] Ng, E., Nestor, S. M., Rabin, J. S., Hamani, C., Lipsman, N., & Giacobbe, P. (2023). Seasonal pattern and depression outcomes from repetitive transcranial magnetic stimulation. Psychiatry Research, 329, 115525. https://doi.org/10.1016/j.psychres.2023.115525

Further Reading

• Lying in Bed All Day, Don’t Want to Go Out, No Motivation for Anything? This May Be Major Depression Symptoms
• How to Help Someone with Depression: What to Say, What to Avoid & When to Get Support
• How to Determine Bipolar Disorder? Understanding Bipolar Affective Disorder Symptoms, Self-Assessment, Treatment, and Differences from Depression