Seasonal depression vs autumn blues: how to tell them apart

October 10 is World Mental Health Day. For 2026 the World Federation for Mental Health (WFMH) chose the theme “Lived Experiences Heard: Real Voices, Real Change”, a call to listen to people who have been through mental health problems themselves. Autumn brings a familiar story: getting up is harder, energy is lower and the sofa beats any plan.

The physics behind it is simple. On October 1, 2026 London had 11 h 39 min of daylight; by October 31 it will have 9 h 45 min, almost two hours less in a single month. New York loses 1 h 17 min over the same weeks. When the UK turns its clocks back on October 25 and the US follows on November 1, sunset jumps to before five o’clock. For most people this means a passing dip, the autumn or winter blues. For some it is seasonal affective disorder (SAD), a recognised form of depression that responds to treatment. Here is how to tell them apart, what the research supports and when to get help.

Why mood drops in October: the daylight numbers

Seasonal mood changes follow the light, not the calendar. The US National Institute of Mental Health (NIMH) explains that shorter days may disturb the molecules that keep serotonin, a brain chemical involved in mood, at normal levels. People with winter-pattern SAD may also produce too much melatonin, the hormone that makes us sleepy. When daylight shrinks, the body clock can drift out of step with your schedule.

The further from the equator, the bigger the swing. We compared four cities at different latitudes: London, New York, Vilnius and Almaty. Day lengths were calculated with the MDU sunrise and sunset calculator, which uses the NOAA solar equations.

In October London loses 1 h 54 min of daylight, roughly four minutes a day, while New York loses 1 h 17 min. By the winter solstice London is down to 7 h 50 min, almost nine hours less than in June. The clock change makes evenings darker still: London sunset moves from 17:50 on October 24 to 16:48 on October 25, New York sunset from 17:55 on October 31 to 16:53 on November 1.

Autumn blues, SAD and depression: what is the difference

The autumn and winter blues

NIMH notes that many people feel “down” when the days get shorter in fall and winter and feel better in spring when longer daylight hours return. The blues are unpleasant but mild. You may want more sleep and comfort food and find mornings harder, yet you keep working, keep in touch with friends and still enjoy the things you normally enjoy. Spring brings it back to normal.

Seasonal affective disorder

The American Psychiatric Association (APA) is clear that SAD is “more than just winter blues”. In the DSM-5-TR it is classified as major depressive disorder with seasonal pattern. According to the APA, about 5% of adults in the US experience SAD, it typically lasts about 40% of the year, and it usually starts between the ages of 18 and 30. Women and younger people are at higher risk, and SAD is more common further from the equator.

NIMH lists three conditions for a diagnosis: symptoms of depression; depressive episodes during a specific season for at least two consecutive years; and more frequent episodes in that season than at other times of year. Winter-pattern SAD typically adds oversleeping, overeating with carbohydrate cravings, weight gain and social withdrawal, the feeling of wanting to hibernate.

Depression without a seasonal pattern

Depression can begin in any season. If low mood, loss of interest and fatigue last more than two weeks and do not lift in spring, it is not a seasonal pattern. Either way, see a doctor: the APA notes that hypothyroidism, hypoglycaemia and viral infections can mimic SAD.

Based on NHS, NIMH and APA descriptions; this is an orientation aid, not a diagnostic tool.

How to tell what is happening to you

Start by noticing. For two weeks, note each evening how long you slept, how long you were outside in daylight and one word for your mood. A precise word (“sad”, “irritable”, “empty”) says more than “bad”. If you get stuck for words, try the emotion wheel. You will see whether low days come and go or have settled in.

What the evidence supports

Light therapy: 10,000 lux in the morning

Light therapy has been a mainstay treatment for winter-pattern SAD since the 1980s. NIMH describes the usual approach: sitting in front of a 10,000 lux light box for about 30 to 45 minutes a day, usually first thing in the morning, from autumn to spring. It is about 20 times brighter than indoor lighting and filters out UV. The APA says most people notice some improvement within one to two weeks.

A 2020 meta-analysis by Pjrek and colleagues in Psychotherapy and Psychosomatics pooled 19 randomised controlled trials. Bright light beat placebo (dim light or an inactive device), with a standardised mean difference of −0.37 for depression scores (18 studies, 610 patients) and a 1.42 times higher chance of responding to treatment. The authors call light therapy effective, but stress that the trials were small to medium-sized, used different methods and carried a moderate to high risk of bias. For that reason the NHS does not usually provide it, though it notes many people find it helps.

Check with a doctor first if you have an eye condition or take light-sensitising medicines. If you buy a lamp, the NHS advises one that is 10,000 lux, UV-free and carries a UKCA or CE mark.

Morning daylight outdoors

The APA notes that more sunlight helps some people with SAD, for example spending time outside or setting up your desk by a window. The NHS advises getting outside in daylight every day. In practice: a 20 to 30 minute walk within two or three hours of sunrise, even when it is overcast. In late October the sun rises around 06:50 in London and 07:25 in New York, so walking or cycling to work is an easy dose of light. You can check sunrise in your city on the sunrise and sunset page.

Exercise

A 2023 umbrella review in the British Journal of Sports Medicine covered 97 systematic reviews (1,039 trials, 128,119 participants). Compared with usual care, physical activity had medium-sized effects on depression (median effect size −0.43), anxiety (−0.42) and distress (−0.60). In autumn, move outdoors in daylight and get both.

A steady sleep schedule

For SAD the NHS recommends going to bed and getting up at the same time every day and not using phones or other devices right before bed. A fixed wake-up time is a strong signal for your body clock; sleeping until noon at the weekend knocks it off course. If your mind races at night, try slow breathing with the breathing timer or ten minutes with the meditation timer.

Vitamin D: an honest look

Vitamin D is often sold as the autumn mood vitamin, but the evidence is mixed at best. NIMH says many people with winter-pattern SAD are low in vitamin D, yet trials have produced conflicting results, some suggesting an effect similar to light therapy and others finding none. The largest trial, VITAL-DEP (JAMA, 2020), randomised 18,353 adults aged 50 and over to 2,000 IU of vitamin D3 a day or placebo for a median of 5.3 years. The risk of depression or clinically relevant depressive symptoms was the same in both groups, and mood scores did not differ. A small Danish trial in people with seasonal symptoms also found no benefit over placebo, though it was underpowered.

The honest summary: vitamin D is not a proven way to lift mood or prevent depression. In the UK, government advice repeated by the NHS is that everyone should consider a daily 10 microgram vitamin D supplement in autumn and winter, but that is for healthy bones, teeth and muscles, which is a separate question. If you suspect a deficiency, ask your doctor about a test and the right dose; NIMH notes that vitamin D can interact with some medicines.

CBT adapted for SAD

Cognitive behavioural therapy (CBT) helps you notice and change unhelpful thoughts and habits. The SAD version (CBT-SAD) usually runs as two group sessions a week for six weeks. It targets thoughts about winter and uses behavioural activation: scheduling enjoyable activities in advance.

In a University of Vermont trial, 177 adults with SAD were randomly assigned to six weeks of CBT-SAD or light therapy. Both worked equally well in the short term, with remission rates on the clinician-rated scale of 47.6% and 47.2%. Two winters later, depression had come back in 27.3% of the CBT-SAD group compared with 45.6% of the light therapy group, which the authors read as a sign that CBT-SAD lasts longer. In England you can self-refer to NHS Talking Therapies from 18 (16 in some areas); in the US, ask your doctor or use findtreatment.gov.

Medication

For moderate or severe depression a doctor may prescribe antidepressants, most often SSRIs; the FDA has approved extended-release bupropion to prevent seasonal episodes. Start or stop them only with medical advice.

A two-week autumn plan

This plan is for the autumn blues and prevention. It does not treat depression, but builds the routine clinicians recommend.

Week 1: light and rhythm

• Days 1–2. Choose a fixed wake-up time and keep it at the weekend too (no more than an hour later). Start a three-line diary: sleep, time outdoors, one word for your mood.
• Days 3–4. Spend 20 to 30 minutes outside within two or three hours of sunrise every day. Move your desk closer to a window.
• Day 5. Put three 30-minute exercise slots in your calendar for the week: a brisk walk, cycling, swimming or a class.
• Days 6–7. Rate your life areas with the wheel of life and pick one to invest in this autumn.

Week 2: activity and connection

• Days 8–9. Behavioural activation: list five things you enjoy (two of them outdoors) and schedule at least one every day.
• Day 10. Meet or call someone you have not spoken to for a while.
• Days 11–12. Evening wind-down: an hour without screens before bed, then five to ten minutes of breathing or meditation. The emotional intelligence test shows how you read and handle emotions.
• Days 13–14. Review your diary. Was mood better on days with more light and movement? If low mood was there most days for two weeks, see a doctor.

If you are curious about Biomind products, the catalogue lists NoStress, a product for the topic of stress and tension. It is not a substitute for daylight, exercise, a sleep routine or professional help.