Seasonal Affective Disorder: Symptoms and Treatment Options
- , by SANUSq Research team
- 13 min reading time
For some people, shorter days bring more than a dip in energy. Every autumn the same low mood returns, settles in for the winter and lifts again in spring. That pattern has a name, seasonal affective disorder (SAD), and it is a form of depression that deserves to be taken seriously. The reassuring part is that it responds well to care, and the answer is not found on a supplement shelf.
What is seasonal affective disorder?
Seasonal affective disorder, often called seasonal depression or winter depression, is depression that follows the calendar. For most people, symptoms appear in autumn or winter and ease off in spring and summer. It is not a passing case of the winter blues but a genuine depressive episode on a seasonal timetable.
Doctors don't treat it as a separate illness so much as a seasonal pattern within major depression (or, less often, bipolar disorder). To make the diagnosis, the low periods need to arrive at the same time of year, clear up fully when that season ends, and repeat over at least two consecutive years.
In a clinical review for family doctors, Galima et al. (2020) describe seasonal affective disorder as a subtype of major depressive or bipolar disorder, with depressive symptoms at a particular time of year and full remission at other times. Possible risk factors include a family history, female sex, living further from the equator and young adulthood, roughly 18 to 30 years of age.
A rarer summer form also exists. Milder seasonal dips in mood are far more common than full SAD, which calls for proper care rather than routine changes alone.
Seasonal depression symptoms to look out for
Seasonal depression symptoms tend to creep in gradually as the evenings draw in. The most common include:
- Persistent low mood for most of the day, on most days.
- Loss of interest or pleasure in things you normally enjoy.
- Tiredness and low energy, even after a full night's sleep.
- Sleeping much more than usual and finding it hard to get up in the morning.
- Changes in appetite, often a strong pull towards sweet or starchy foods, sometimes with weight gain.
- Difficulty concentrating and a sense of moving through the day in slow motion.
Oversleeping and craving carbohydrates are especially typical of the winter pattern. Many of these symptoms can also have other causes, such as an underactive thyroid or anaemia, which is one more reason to see a doctor rather than self-diagnose.
Why winter? The role of light
The exact cause isn't fully understood, but one thread runs through the research: the drop in natural daylight. Less light, especially in the morning, appears to unsettle the body clock (the circadian rhythm) and the brain's chemical messengers involved in mood and sleep.
Two mechanisms are most studied. With little morning light, the body clock may drift later, leaving people sluggish and low. Reduced light is also thought to affect serotonin, which helps regulate mood, while long hours of darkness alter the release of melatonin, the sleep hormone. Both help explain why light sits at the centre of treatment.
Seasonal affective disorder treatment: what works
The news here is good. Seasonal affective disorder treatment rests on three established approaches, used alone or together, chosen with a health professional according to how severe the symptoms are and what suits the person.
Light therapy
Light therapy means sitting near a specially designed light box for a set time each morning, usually from autumn through to spring. These lamps are far brighter than ordinary household lighting. Typical guidance is 2,500 to 10,000 lux for 30 to 60 minutes at the same time each day, with the exact routine depending on the device and how a person responds. Many people notice a difference within one to two weeks.
A meta-analysis by Golden et al. (2005) found that bright light treatment and dawn simulation both significantly reduced the severity of depression in seasonal affective disorder, with effect sizes comparable to those seen in most antidepressant drug trials.
A more recent meta-analysis of 19 randomised trials by Pjrek et al. (2020) found bright light therapy was superior to placebo for depression ratings and response to treatment. The authors concluded it can be regarded as an effective treatment for SAD, while calling for larger, higher-quality trials.
Light therapy is a treatment, not a gadget, and it comes with rules of use. People with bipolar disorder, certain eye conditions, or who take medicines that increase sensitivity to light should only use it under medical supervision. It is worth involving your doctor before buying a lamp.
Talking therapy (CBT)
Cognitive behavioural therapy (CBT) is a structured form of talking therapy. A version tailored to SAD helps people challenge negative thoughts about winter and plan rewarding activities, and its benefit seems to last.
In a randomised trial of 177 adults with seasonal depression, Rohan et al. (2016) compared six weeks of SAD-tailored CBT with six weeks of light therapy. The two did equally well during the first winter of follow-up. By the second winter, depression had returned in 27.3% of the CBT group compared with 45.6% of the light therapy group, suggesting the benefits of CBT may be more durable.
Antidepressant medication
For moderate to severe SAD, a doctor may prescribe an antidepressant. In people whose depression returns every year, some doctors suggest starting treatment in early autumn, before symptoms take hold.
A Cochrane review by Gartlehner et al. (2019), drawing on three trials with 1,100 participants, found moderate-quality evidence that bupropion XL reduced the recurrence of depressive episodes in people with a history of SAD. It also caused more headaches, insomnia and nausea than placebo, and most people at risk would not benefit, so the authors stressed that patient preference should guide the choice.
A separate Cochrane review on treating an active episode, by Nussbaumer-Streit et al. (2021), found the evidence for modern antidepressants in SAD was limited to a few small trials. Two suggested fluoxetine and light therapy worked about equally well, but no firm conclusions were possible.
What about vitamin D and supplements?
People with SAD often have low vitamin D levels, unsurprising given how little winter sun many of us get. Vitamin D contributes to the normal function of the immune system and to the maintenance of normal bones, and low levels are worth correcting for those reasons. But the research doesn't show that it relieves seasonal depression.
In a small double-blind trial, Frandsen et al. (2014) gave 34 healthcare workers with seasonal symptoms either 70 µg of vitamin D a day or a placebo for three months over winter. Symptoms improved in both groups as spring approached, with no significant difference between them. The authors noted the study was underpowered and could not assess people with low starting levels.
The Galima review cited above likewise describes the evidence for vitamin D supplementation in SAD as inconclusive. If a blood test shows you are deficient, correcting it is sensible as part of your overall care, decided with your doctor. It belongs alongside the recognised treatments, never in place of them.
A word of caution about St John's wort
St John's wort is often called a natural antidepressant, but the evidence in SAD is thin, and it interacts with many medicines.
In a review of St John's wort interactions, Nicolussi et al. (2020) describe how it speeds up the breakdown of many drugs in the body. It has been shown to alter the levels and effectiveness of medicines including the contraceptive pill, warfarin, digoxin, simvastatin and drugs used after organ transplants, where reduced levels led to acute rejection in two heart transplant patients.
It should also never be combined with prescribed antidepressants. Don't take St John's wort without talking to your doctor or pharmacist first.
Everyday habits that help
Alongside proper care, a few simple habits can support your mood through the winter:
- Get daylight early. A morning walk, open curtains and a seat near the window all help, even on overcast days.
- Keep moving. Regular physical activity, ideally outdoors, is good for mood and energy.
- Keep a steady sleep routine. Going to bed and getting up at regular times helps anchor the body clock.
- Stay connected. Winter nudges us towards isolation, so keep up contact and plan small things to look forward to.
- Eat well. Regular, balanced meals help, with an eye on the sugar cravings that are so common with SAD.
These habits don't replace treatment once SAD has taken hold, but they support it, and for milder winter dips they are sometimes enough.
When to seek help
Seasonal affective disorder is a real medical condition, and it can be treated effectively. If your mood stays low for weeks, if symptoms are affecting your work, relationships or daily life, or if the same pattern returns every winter, talk to your GP or a mental health professional.
If you feel hopeless or have thoughts of harming yourself, don't wait. Contact your doctor, emergency services or a crisis line in your country straight away, or reach out to someone you trust. You don't have to go through this alone.
The bottom line
Seasonal affective disorder is depression linked to the seasons: real, but very responsive to care. The approaches that work are light therapy, talking therapy and, where needed, medication, all best arranged with a health professional. Vitamin D has a place if you are genuinely deficient, but it is not a treatment for SAD. The most useful first step is a conversation with your doctor.
Frequently asked questions
Is seasonal affective disorder just the winter blues?
No. It is a recognised form of depression with a seasonal pattern, more intense and disruptive than an ordinary winter slump, and it responds well to treatment.
What are the main symptoms of seasonal depression?
Persistent low mood, loss of interest in things you usually enjoy, tiredness, sleeping more than usual, craving sweet or starchy foods and difficulty concentrating. They typically start in autumn and lift in spring.
What is the most effective treatment for seasonal affective disorder?
Light therapy, cognitive behavioural therapy and antidepressants, alone or combined, are the main approaches. Light therapy often works within a couple of weeks, while SAD-tailored CBT appears to have more lasting effects in later winters. A health professional can help you choose.
Does vitamin D help seasonal depression?
Low vitamin D is common in winter, but trials of supplements for SAD have produced mixed results and don't show a reliable effect on symptoms. If a blood test shows a deficiency, correcting it with your doctor's guidance is sensible, but it doesn't replace recognised treatment.
How does light therapy work?
You sit near a bright light box, typically for 30 to 60 minutes each morning, usually from autumn to spring. It is a treatment in its own right, best set up with a health professional, particularly if you have bipolar disorder or an eye condition.
Is St John's wort a good option for SAD?
Not without medical advice. Its benefit in SAD hasn't been shown, and it interacts with many medicines, including the contraceptive pill, blood thinners and antidepressants. Never take it on your own initiative.
References
- Galima SV, Vogel SR, Kowalski AW. Seasonal affective disorder: common questions and answers. American Family Physician. 2020;102(11):668–672. PMID 33252911
- Golden RN, Gaynes BN, Ekstrom RD, et al. The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. American Journal of Psychiatry. 2005;162(4):656–662. PMID 15800134
- Pjrek E, Friedrich ME, Cambioli L, et al. The efficacy of light therapy in the treatment of seasonal affective disorder: a meta-analysis of randomized controlled trials. Psychotherapy and Psychosomatics. 2020;89(1):17–24. PMID 31574513
- Rohan KJ, Meyerhoff J, Ho SY, Evans M, Postolache TT, Vacek PM. Outcomes one and two winters following cognitive-behavioral therapy or light therapy for seasonal affective disorder. American Journal of Psychiatry. 2016;173(3):244–251. PMID 26539881
- Gartlehner G, Nussbaumer-Streit B, Gaynes BN, et al. Second-generation antidepressants for preventing seasonal affective disorder in adults. Cochrane Database of Systematic Reviews. 2019;3(3):CD011268. PMID 30883669
- Nussbaumer-Streit B, Thaler K, Chapman A, et al. Second-generation antidepressants for treatment of seasonal affective disorder. Cochrane Database of Systematic Reviews. 2021;3(3):CD008591. PMID 33661528
- Frandsen TB, Pareek M, Hansen JP, Nielsen CT. Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial. BMC Research Notes. 2014;7:528. PMID 25125215
- Nicolussi S, Drewe J, Butterweck V, Meyer Zu Schwabedissen HE. Clinical relevance of St. John's wort drug interactions revisited. British Journal of Pharmacology. 2020;177(6):1212–1226. PMID 31742659
Read more on the blog
- Things You Should Know About Depression →
- How Light and Screens Affect Your Sleep →
- Vitamin D in Winter: Benefits, Deficiency, and How to Get Enough →
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