Seasonal depression: winter blues or a depressive disorder, why it happens and what helps

Feeling a little low in autumn and winter, as the days get shorter, and better again in spring is common. This mild change, often called the “winter blues”, is not a diagnosis. Seasonal depression goes further: it is depression that affects how you think and act, and your daily life (NIMH, 2023; APA, 2024).

The World Health Organization’s classification (ICD-11) does not treat seasonal depression as a separate illness. In recurrent depressive disorder or bipolar disorder, it adds the description “seasonal pattern” when mood episodes regularly start at a particular time of year and ease once that season passes; in recurrent depressive disorder, most depressive episodes must follow this pattern (WHO, 2024). The American Psychiatric Association’s manual (DSM-5-TR) sees it as a type of depression, “major depressive disorder with seasonal pattern” (APA, 2024): episodes must come in the same season for at least 2 consecutive years and fully lift when the season ends, and over a lifetime seasonal episodes must far outnumber non-seasonal ones (Galima et al., 2020). Even so, people with seasonal depression do not necessarily have symptoms every single year (NIMH, 2023).

Becoming depressed because of stress that returns at the same time every year, such as the holidays or year-end, is not counted as a seasonal pattern. Seasonal depression follows changes in daylight, not the calendar (WHO, 2024; NIMH, 2023). Depression brought on by that kind of stress still deserves care all the same.

mind.io does not offer a seasonal depression test. This guide uses research to describe the winter and summer patterns, how common seasonal depression is and what lies behind the idea of “autumn blues”, why it happens, treatments such as light therapy and cognitive behavioural therapy, what you can try on your own and the evidence on vitamin D, and where to get help.

The winter pattern usually starts in late autumn or early winter and lifts in spring or summer. On top of the usual signs of depression, such as low mood and loss of interest, people often sleep far more, crave carbohydrates and eat more so that they gain weight, and withdraw from others as if hibernating (NIMH, 2023). Thoughts of suicide or self-harm can also come (NHS, 2025). Not everyone has this profile, though: among people with seasonal depression seen at Japanese university outpatient clinics, 20% to 30% showed the increase in sleep and appetite (Sakamoto et al., 1993).

Less often, at least in Western studies, depression comes in spring or summer instead. In this summer pattern, people tend to sleep badly and lose their appetite and weight, and to feel more restless or anxious (NIMH, 2023; Wehr et al., 1991). In East Asian countries such as Korea, with hot, humid summers, some people name summer rather than winter as their hardest season, and researchers note that seasonal questionnaires designed in the West struggle to identify the winter pattern there (Yeom et al., 2025). There is no treatment designed specifically for the summer pattern yet (NIMH, 2023).

Some people have a period of feeling more energetic than usual at the start of spring or summer (NHS, 2025). In bipolar disorder, too, mania tends to peak in spring and summer and depression in early winter (Geoffroy et al., 2014). If you are low every winter and have had times in spring when you slept much less and felt unusually high, it could be bipolar disorder, so be sure to tell your doctor.

Feeling tired and flat every winter is not always seasonal depression. Physical problems such as an underactive thyroid, low blood sugar or tiredness after an infection can look similar, so they are worth checking with a doctor (APA, 2024). The general symptoms of depression are covered in depression symptoms, and unexplained tiredness and lack of energy in feeling unmotivated and drained.

Measured with diagnostic interviews, seasonal depression is rarer than people often assume. In a US national survey of 8,098 people, 0.4% had ever had major depression with a seasonal pattern, and 1.0% when milder depression was included (Blazer et al., 1998). Among 781 residents of Toronto the figure was 2.9%, or 11% of those who had had major depression (Levitt et al., 2000), and in North Wales it was 2.4% (Michalak et al., 2001). In 20 retrospective surveys, which ask people to recall past seasons, figures ranged from 0% to 9.7% (Magnusson, 2000), but questionnaires that ask about the seasons directly invite memory and confirmation bias and tend to overestimate (Øverland et al., 2019).

The idea that it is more common the further north you go is only half right. A review of prevalence studies found more seasonal depression at higher latitudes in North America but no clear link across all the studies, and the authors suggested that climate, genetic vulnerability and social and cultural context may matter more (Mersch et al., 1999). It usually begins in young adulthood and is often reported to be more common in women (NIMH, 2023), but a US survey using diagnostic interviews found a seasonal pattern more often in men and older people with major depression, so findings disagree (Blazer et al., 1998).

There are few Korean data. In a study that gave a seasonality questionnaire to 552 adults in the Seoul area with no history of mental illness, 16.2% met the questionnaire criteria for seasonal depression or a milder form, and those with marked seasonal changes named winter (41.6%) and summer (38.2%) about equally often as their worst time (Baek et al., 2015). These are questionnaire criteria, not diagnoses. A survey of 1,276 civil servants in Nagoya, Japan, likewise estimated 0.86% for the winter pattern and 0.94% for the summer pattern (Ozaki et al., 1995).

Many people feel the “autumn blues”, but whether people as a whole become clearly more depressed in autumn or winter is disputed. A systematic review of 41 studies found that 13 showed more depression in winter (Øverland et al., 2019). Canadian national surveys of more than 500,000 people found that reports of a depressive episode were 70% higher in January than in August (Patten et al., 2017), yet in a survey of 34,294 US adults, depression scores were unrelated to season or sunlight (Traffanstedt et al., 2016). A US study that surveyed the same people many times from age 14 to 36 found symptoms highest in early winter and lowest in early autumn, but the differences were small (Kerr et al., 2013). Mood shifting a little as the seasons change is common; what matters is depression that returns in the same season every year and disrupts daily life.

The exact cause is not yet known. It is thought to be linked to the shorter daylight of winter, with changes in the body clock, melatonin and serotonin all discussed (NHS, 2025; NIMH, 2023). One of the most studied explanations is the body-clock hypothesis: in winter the internal clock falls behind outside time or the sleep schedule, and bright morning light moves it earlier and eases symptoms. Some studies support it and some do not, so it is best seen as one factor involved in many cases (Levitan, 2007).

In people with seasonal depression, the nightly period of melatonin release was longer in winter than in summer, while in healthy people it did not change, but the researchers themselves said this does not prove a cause (Wehr et al., 2001). A brain-imaging study of 88 healthy people found more of the protein that takes serotonin back up in autumn and winter (Praschak-Rieder et al., 2008). Such studies are small, and seasonal depression does not seem to have a single biological cause (Lam & Levitan, 2000). There is no basis for saying flatly that the autumn blues are “hormonal”.

In a study of 4,639 twins, genes explained at least 29% of individual differences in seasonal changes in mood and behaviour (Madden et al., 1996). Negative thoughts about the season, such as “winter is just awful” or “once it gets dark I can’t do anything”, are also common; whether they are a cause or a result is unclear, but they can be worked on in treatment (NIMH, 2023).

Light therapy means sitting in bright, UV-filtered light for a set time. In a meta-analysis of 19 randomised controlled trials, bright light lowered depression scores more than dim light or sham devices (18 trials, 610 patients), and made a response to treatment 1.42 times as likely. The effect is small to moderate, though, and most studies were small, with a moderate to high risk of bias (Pjrek et al., 2020). Many people also respond to sham devices: in a 4-week trial, 61% responded to morning light and 32% to a sham device, and it took at least 3 weeks for a clear advantage over the sham to appear (Eastman et al., 1998).

This is why bodies rate it differently. The 2023 guideline of the Canadian Network for Mood and Anxiety Treatments (CANMAT) recommends light therapy as a first-line treatment on its own for winter-pattern seasonal depression (Lam et al., 2024). The UK’s National Institute for Health and Care Excellence (NICE), by contrast, says people who want to try it should be told that the evidence for its efficacy is uncertain (NICE, 2022), and the NHS says it is not usually available on the NHS, while adding that many people find it helps (NHS, 2025).

In a trial at 4 Canadian centres that divided 96 people for 8 weeks, those who had 10,000-lux light for 30 minutes each morning and those who took an antidepressant both had a 67% response rate, with similar remission rates of 50% and 54%. The light group improved faster in the first week, and side effects such as agitation and sleep problems were more common with the medicine (Lam et al., 2006). A Cochrane review found only one small trial comparing an antidepressant with placebo for seasonal depression, with no clear difference, while two trials comparing antidepressants with light therapy (136 people) found similar effects (Nussbaumer-Streit et al., 2021). General information on antidepressants for depression is in antidepressants and psychiatric medication.

Cognitive behavioural therapy adapted for seasonal depression involves planning and doing enjoyable activities even in winter, and examining thoughts about winter such as “once it gets dark I can’t do anything”. In a US trial of 177 people, 6 weeks of group CBT (twice a week, 12 sessions in all) and daily morning light therapy had similar remission rates of 47.6% and 47.2% (Rohan et al., 2015). By the second winter, depression had returned in 27.3% of the CBT group, fewer than in the light group (45.6%), though only 34.9% of the light group were still using their device the following year (Rohan et al., 2016).

If depression returns every winter, treatment can also start before symptoms do. A Cochrane review of three trials (1,100 people) in which one antidepressant was taken from autumn found the risk of recurrence fell by about 44%, but side effects such as headache, insomnia and nausea also rose, and even among high-risk people three in four did not benefit (Gartlehner et al., 2019). Whether light therapy or mindfulness-based cognitive therapy can prevent winter depression is still unclear, with just one trial of 46 people for each (Nussbaumer-Streit et al., 2019; Forneris et al., 2019). Talk to a doctor before starting or stopping any medicine.

If you try light therapy, the usual approach in guidelines is 10,000-lux white light for about 30 minutes a day, soon after waking (Lam et al., 2024). It usually starts to work within 1 to 3 weeks (Ravindran et al., 2016), and because symptoms often return quickly if it is stopped too early, it is usually continued all winter (Westrin & Lam, 2007). Santé.fr describes sitting about 30 cm from a 10,000-lux lamp (Santé.fr, 2025); the further away, the less light reaches your eyes, so if you buy a device, check that it is bright enough and filters out UV light (NHS, 2025). Many so-called “depression lamps” sold to the public have not been properly shown to work, and the NHS and Santé.fr both advise talking to a doctor before you start (Santé.fr, 2025; NHS, 2025).

Side effects are usually mild, such as nausea, headache or feeling jittery or on edge (Terman & Terman, 1999), and evening light can disturb sleep, which is why it is usually used in the morning (Labbate et al., 1994). If you have an eye condition or take medicines that make you more sensitive to light, see an eye doctor before starting (Galima et al., 2020; Santé.fr, 2025). In trials of light therapy added to medication, people with bipolar depression switched into a high no more often than with control conditions (Lam et al., 2020), but ICD-11 lists light therapy among treatments that can trigger mania or hypomania (WHO, 2024). If you have bipolar disorder or have had high periods, use it only after talking to your doctor, and if you sleep much less or feel unusually high after starting, stop and contact them straight away.

“Dawn simulation”, which gradually brightens the room towards the end of sleep, did better than sham light and about as well as bright light therapy in small trials (Avery et al., 2001; Terman & Terman, 2006), but the studies are few and old. There is no evidence that blue-enriched light works better than ordinary white light (Gordijn et al., 2012; Anderson et al., 2016). Negative ion generators showed effects in a few small trials but are not a recommended treatment, and light therapy trials have actually used weak ion generators as the sham treatment (Perez et al., 2013; Pjrek et al., 2020). Reducing blue light at night (for sleep) and getting bright light in the morning (for seasonal depression) are different questions. How light moves the body clock earlier or later, and how morning people differ from night owls, is covered in Morning people and night owls.

The NHS advises getting outside in daylight as much as you can, exercising regularly, staying in touch with family and friends, and going to bed and getting up at the same time every day. It also advises against drinking too much alcohol or using a smartphone right before bed (NHS, 2025). Good sleep habits and exercise have not been tested as treatments in well-designed trials, but they carry little risk and have other benefits (Galima et al., 2020). Do not look straight at the sun, though, and do not think of outdoor light as a replacement for light therapy. Keeping a steady wake-up time is covered in insomnia: what helps.

The idea that “winter means too little sun, too little vitamin D and so depression” is only half right. Observational studies found more depression in people with low vitamin D levels, but cannot show it is the cause (Anglin et al., 2013). In a 12-week trial in health workers with seasonal symptoms, vitamin D did no better than placebo (Frandsen et al., 2014), and in a large trial in which 18,353 people aged 50 and over took it for more than 5 years (median 5.3 years), it did not prevent depression (Okereke et al., 2020). Meta-analyses of depressive symptoms in general disagree: one found no effect (Gowda et al., 2015), another a small short-term reduction (Ghaemi et al., 2024). Vitamin D does not replace light therapy or treatment for depression and can interact with other medicines, so if you suspect a deficiency, talk to a doctor about testing and taking it (NIMH, 2023).

See a doctor if low mood or loss of interest keeps returning in the same season every year and your work, studies or relationships suffer. The same goes if you think you might have seasonal depression, or if treatment is not helping after a diagnosis (NHS, 2025). Symptoms may ease on their own when spring comes, but treatment can bring improvement sooner (APA, 2024), and if it happens every year you can make a plan before the next autumn (NIMH, 2023). In a North Wales survey, most people with seasonal depression had never been diagnosed with it (Michalak et al., 2001).

Children and teenagers can have seasonal depression too, but research is very limited (Swedo et al., 1995). Sleeping and eating more are more common in teenage depression than in adults, whatever the season (WHO, 2024), so if you are worried, start with a child and adolescent mental health specialist, and talk to a doctor before using a light box with a child. The depression check-in (PHQ-9) only asks about the past two weeks, so it cannot show a seasonal pattern. Take it during your hardest season, and keep notes over several months on when your mood, sleep and appetite change and when they come back; this helps a clinician.

If you live outside Korea, start with a family doctor or your local mental health services, and see the crisis lines just below. In Korea, you can get help from a psychiatrist or your city, county or district mental health welfare centre, and the mental health crisis line 1577-0199 (24 hours) connects you to a nearby centre (Ministry of Health and Welfare, 2025). The conditions for the 2026 counselling voucher are in depression: what helps. mind.io does not offer a seasonal depression test, and self-checks are not a diagnosis.

Seasonal depression can also bring thoughts of suicide or self-harm (NHS, 2025). Keep looking after yourself even in spring, when mood starts to lift. If you have thoughts of harming yourself, please do not carry them alone. Reach out to a crisis line right away: call or text 988 in the US and Canada, call Samaritans on 116 123 in the UK and Ireland, or find a line at findahelpline.com elsewhere. If you are in immediate danger, contact your local emergency services.

Q. I feel low every autumn. Is that an illness? A. Mood shifting as the seasons change is common and usually mild (NIMH, 2023). The evidence that people in general become depressed in autumn is mixed (Øverland et al., 2019). If depression returns in the same season every year and disrupts daily life, see a doctor.

Q. Can I buy any light box? A. Talk to a doctor before you start, and check that it is bright enough and filters out UV light (NHS, 2025), especially if you have an eye condition or bipolar disorder (Santé.fr, 2025). Ordinary indoor lighting is far dimmer than the devices used in research (NIMH, 2023), and there is no evidence that products emphasising blue light work better than ordinary white light (Gordijn et al., 2012; Anderson et al., 2016).

Q. Will vitamin D help? A. In a trial of vitamin D for seasonal symptoms, it did no better than placebo (Frandsen et al., 2014), and a large trial found it did not prevent depression (Okereke et al., 2020). If you suspect a deficiency, talk to a doctor about testing and taking it.

Q. I actually get depressed in summer. Is that seasonal too? A. There is a summer pattern. Sleeping badly and losing appetite are common (NIMH, 2023), and in a Korean survey many people named summer as their hardest time (Baek et al., 2015). There is no treatment designed for the summer pattern yet, so discuss it with a doctor.

Q. Can I use light therapy if I have bipolar disorder? A. Only after talking to your doctor. Light therapy is listed among treatments that can trigger mania or hypomania (WHO, 2024), and one review found that, of 16 people with rapid-cycling bipolar disorder, 18.8% switched into a high (Benedetti, 2018).

Q. Does mind.io have a seasonal depression test? A. mind.io does not offer a seasonal depression test. Seasonal depression is diagnosed by a professional who looks at the seasonal pattern over several years. The depression check-in (PHQ-9) is not a seasonal depression test, but it lets you look at depressive symptoms over the past two weeks.

Q. It is so hard that I have thoughts of harming myself. A. Please do not carry this alone. Reach out to a crisis line right away: call or text 988 in the US and Canada, call Samaritans on 116 123 in the UK and Ireland, or find a line at findahelpline.com elsewhere. If you are in immediate danger, contact your local emergency services.

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