What is Seasonal Affective Disorder (SAD) and what are my treatment options?

Many people feel down during the dark winter months. For some, the "winter blues" become a serious depression called seasonal affective disorder (SAD). SAD is a type of depression that returns at the same time each year, most often in the fall and winter, and improves in the spring. It was first described in 1984 by Dr. Norman Rosenthal and colleagues at the US National Institute of Mental Health. Its exact causes are not fully understood, but shorter days and less daylight are thought to disrupt the body clock, sleep and mood. The good news is that SAD is treatable.

What is the difference between the winter blues and SAD?

The winter blues are common and mild: you may feel more tired and less motivated, but you can still manage work and daily life. SAD is a form of major depression. Symptoms are strong enough to affect your work, relationships and daily functioning, and they come back in the same season for at least two years in a row.

What are the symptoms of SAD?

Winter SAD often includes:

• Sleeping much more than usual and having trouble waking up
• Feeling tired during the day and having low energy
• Increased appetite, carbohydrate cravings and weight gain
• Trouble concentrating
• Withdrawing from friends and activities
• Irritability
• Feeling sad, hopeless, worthless or guilty
• Losing interest in activities you usually enjoy
• Lower interest in sex
• Thoughts of death or suicide

Less commonly, depression follows a summer pattern, with poor sleep, low appetite and weight loss. Some people with seasonal depression have bipolar disorder, with periods of high energy or elevated mood (hypomania) in spring or summer. This matters because light therapy and antidepressants can trigger these highs, so tell your doctor if you have ever had them.

If you have thoughts of suicide, get help right away. In Canada, you can call or text 9-8-8 at any time.

Who is affected by SAD?

SAD is more common in places farther from the equator, where winter days are shorter. In Canada, a few percent of people have SAD, and many more have milder winter blues. SAD usually starts in young adulthood, and women are diagnosed much more often than men.

Should you have your thyroid checked?

Yes. Thyroid function is a major factor in mental health. An underactive thyroid (hypothyroidism) can cause tiredness, low mood, weight gain, oversleeping and trouble concentrating, which look very much like winter depression. Ask your doctor for a simple blood test (TSH) before or alongside treatment for SAD, especially if your symptoms do not improve. Treating a thyroid problem can improve both energy and mood. Read more about thyroid function and depression.

How does light therapy work?

Light therapy uses a lightbox that gives off bright light similar to outdoor daylight. Canadian guidelines (CANMAT) recommend light therapy as a first-line treatment for depression with a seasonal pattern. In a Canadian study (CAN-SAD), light therapy worked as well as the antidepressant fluoxetine, with about two in three people improving in both groups, and light therapy started working faster.

How to use a lightbox:

• Choose a lightbox designed for SAD that gives 10,000 lux of white light and filters out UV light.
• Sit about 30 to 60 cm away, with the light shining toward your eyes from the side or above. You do not need to look directly at it.
• Use it for 20 to 30 minutes each morning, soon after waking, every day during the fall and winter.
• Improvement usually begins within one to two weeks. Symptoms often return if you stop, so most people continue until spring.

Side effects are usually mild and include headache, eye strain, nausea and feeling on edge. Using light late in the day can cause trouble sleeping. Talk to your doctor before starting if you have bipolar disorder, an eye condition such as macular degeneration or retinal disease, or take medications that make your skin or eyes more sensitive to light.

Can cognitive behavioural therapy (CBT) help SAD?

Yes. CBT for SAD teaches skills to manage negative thoughts and to stay active during the winter. In a study of 177 adults with SAD, six weeks of CBT and six weeks of light therapy worked equally well at first. Two winters later, depression came back in 27% of people who had CBT, compared with 46% of those who had light therapy. One reason may be that many people stop using their lightbox in later winters, while CBT skills last.

Does exercise help?

Regular physical activity helps depression in general and is a good addition to other SAD treatments. Exercising outdoors in daylight gives you both activity and light. In a Finnish study of office workers in winter, exercising under bright light improved mood and energy more than exercising under ordinary indoor light.

Does vitamin D help SAD?

The body makes vitamin D from sunlight, and levels drop in winter in Canada. Low vitamin D has been linked to depression, but supplements have not been shown to treat or prevent it. In a trial of healthcare workers, vitamin D did not improve seasonal symptoms, and a large trial of more than 18,000 adults found that vitamin D did not prevent depression. Health Canada recommends vitamin D for general health in many adults, especially in winter. Do not take more than 4,000 IU (100 micrograms) a day unless your doctor advises it.

Which antidepressants are used for SAD?

When SAD is moderate to severe, or when light therapy and CBT are not enough, an antidepressant may help. Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine (Prozac) and sertraline (Zoloft), have been shown to help. Light therapy and an antidepressant can also be used together.

Bupropion XL (Wellbutrin XL) is approved to prevent seasonal depression. In three trials with more than 1,000 people, starting bupropion XL in the fall, before symptoms began, lowered the risk of a winter episode by 44% compared with a placebo.

Like all medications, antidepressants can have side effects, such as nausea, sleep changes, headache, sexual side effects and, with some, weight gain. Do not stop an antidepressant suddenly without talking to your doctor.

How can a pharmacogenetic test help?

Your genes affect how your body processes many antidepressants. For example, CYP2C19 affects escitalopram and sertraline, CYP2D6 affects paroxetine and vortioxetine, and CYP2B6 affects bupropion and sertraline. If your body breaks down a medication too slowly, side effects are more likely. If it breaks it down too quickly, the medication may not work at the usual dose.

A Pillcheck test shows how your genes affect antidepressants and many other medications. Pillcheck reports on 24 genes, increasing coverage with new guidelines and drug labels (see the genes tab), and covers 355 medications, which account for over 70% of dispensed prescriptions. A Pillcheck pharmacist reviews your results together with all your medications and writes recommendations for you to share with your doctor.

Summary

• SAD is a form of depression that returns at the same time each year, most often in fall and winter.
• Ask your doctor to check your thyroid function, because an underactive thyroid can cause similar symptoms.
• Light therapy is a first-line treatment. Use a 10,000-lux lightbox for 20 to 30 minutes each morning.
• CBT works as well as light therapy in the short term and may protect better against future winters.
• Exercise and daylight help. Vitamin D supplements have not been shown to treat depression.
• Antidepressants can help, and bupropion XL started in the fall can prevent winter episodes.
• Pharmacogenetic testing can help your doctor choose an antidepressant and dose that suit you.

Frequently asked questions

When should I start light therapy?

Many people start in early fall, when symptoms usually begin, and continue until spring. Your doctor can help you decide on timing.

Can I use a regular lamp instead of a lightbox?

No. Regular indoor lights are much dimmer than the 10,000 lux used in studies. Use a lightbox designed for SAD.

Is light therapy safe with antidepressants?

Usually, yes, and the two are often used together. Check with your doctor or pharmacist if you take medications that make you sensitive to light, or if you have bipolar disorder or an eye condition.

Can a genetic test tell me which antidepressant will work for SAD?

No test can promise that a medication will work. A pharmacogenetic test shows how your body processes many antidepressants, which helps your doctor choose a medication and dose with a lower risk of side effects.

References

1. Rosenthal NE, et al. Seasonal affective disorder. A description of the syndrome and preliminary findings with light therapy. Arch Gen Psychiatry. 1984;41(1):72-80.
2. Lam RW, Levitt AJ, Levitan RD, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. Am J Psychiatry. 2006;163(5):805-812.
3. Lam RW, Kennedy SH, Adams C, et al. Canadian Network for Mood and Anxiety Treatments (CANMAT) 2023 Update on Clinical Guidelines for Management of Major Depressive Disorder in Adults. Can J Psychiatry. 2024;69(9):641-687.
4. Rohan KJ, et al. Randomized Trial of Cognitive-Behavioral Therapy Versus Light Therapy for Seasonal Affective Disorder: Acute Outcomes. Am J Psychiatry. 2015;172(9):862-869.
5. Rohan KJ, Meyerhoff J, Ho SY, et al. Outcomes One and Two Winters Following Cognitive-Behavioral Therapy or Light Therapy for Seasonal Affective Disorder. Am J Psychiatry. 2016;173(3):244-251.
6. Partonen T, Leppämäki S, Hurme J, Lönnqvist J. Randomized trial of physical exercise alone or combined with bright light on mood and health-related quality of life. Psychol Med. 1998;28(6):1359-1364.
7. Frandsen TB, et al. Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial. BMC Res Notes. 2014;7.
8. Okereke OI, Reynolds CF, Mischoulon D, et al. Effect of Long-term Vitamin D3 Supplementation vs Placebo on Risk of Depression or Clinically Relevant Depressive Symptoms and on Change in Mood Scores: A Randomized Clinical Trial. JAMA. 2020;324(5):471-480.
9. Moscovitch A, et al. A placebo-controlled study of sertraline in the treatment of outpatients with seasonal affective disorder. Psychopharmacology (Berl). 2004;171(4):390-397.
10. Modell JG, Rosenthal NE, Harriett AE, et al. Seasonal affective disorder and its prevention by anticipatory treatment with bupropion XL. Biol Psychiatry. 2005;58(8):658-667.
11. Bousman CA, Stevenson JM, Ramsey LB, et al. Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6, CYP2C19, CYP2B6, SLC6A4, and HTR2A Genotypes and Serotonin Reuptake Inhibitor Antidepressants. Clin Pharmacol Ther. 2023;114(1):51-68.