Winter Blues or Seasonal Affective Disorder? What Helps

The clocks have gone back on both sides of the Atlantic. In London and Berlin the sun now sets around half past four, and in New York and Chicago it’s down before five. If you’ve felt flatter since, sleeping longer and craving bread and sweets, you have plenty of company.

For most people this is the winter blues, a dip that makes the dark months heavier but leaves daily life intact. Seasonal affective disorder (SAD) is depression that keeps returning at the same time of year, usually autumn and winter, and lifts in spring. It’s far less common, and treatable. Bright light therapy and a winter-specific form of cognitive behavioral therapy (CBT) are the best-studied treatments.

How to Tell Winter Blues from Seasonal Affective Disorder

The US National Institute of Mental Health (NIMH) describes SAD as recurring depression with symptoms that last about four to five months a year. That means low mood or lost interest in things you enjoy for most of the day, nearly every day, for at least two weeks. Winter SAD can also bring oversleeping, carbohydrate cravings with weight gain, and a pull to withdraw from people.

A diagnosis also needs the pattern: episodes in the same season for at least two years running, more often than at other times of year. The winter blues point the same way without the weight. You may sleep more and feel slower, but you still work, see people and enjoy things.

See a doctor if low mood or lost interest has lasted most days for two weeks, or it’s getting in the way of work, sleep or looking after yourself. You don’t need a second winter to prove the pattern. If you have thoughts of harming yourself, get help today from your doctor, emergency services, 988 in the US or Samaritans (116 123) in the UK and Ireland.

How Common SAD Is, and Where Latitude Fits

SAD is thought to become more common the farther you live from the equator, and NIMH notes it is more frequent in Alaska or New England than in Texas or Florida, and much more common in women. Iceland, just south of the Arctic Circle, has long been the awkward case: earlier research there found surprisingly low rates.

A 2026 study drew a random sample from Iceland’s population registry. Of 1,384 people who completed a standard seasonality questionnaire, about 18% reported marked seasonal swings in mood and behavior. Phone interviews with 111 of the high scorers found 18 who met the criteria for SAD, an estimated 2.2% of the population. Only about 15% of those invited took part, so the figures are rough. The authors’ point: seasonal swings and clinical SAD differ, and surveys that blur them can’t settle how much latitude matters.

Zelinski, L. et al. (2026). “Prevalence of seasonal affective disorder and seasonality of mood and behaviour in Iceland – Methodological implications for revisiting the latitude hypothesis.” Journal of Affective Disorders, 398, 121057.

What Light Therapy Can and Can’t Do

Light therapy has been a mainstay for winter SAD since the 1980s. You sit near a light box giving off 10,000 lux, about 20 times brighter than ordinary indoor light by NIMH’s estimate, usually first thing each morning.

A 2020 meta-analysis from the Medical University of Vienna pooled 19 randomized trials, with more than 600 patients in all, comparing bright light with dim light or a placebo device. People given bright light ended with lower depression scores and were about 1.4 times as likely to respond to treatment. The effect was modest, and the trials were small to medium-sized, varied in design and had a moderate to high risk of bias.

Pjrek, E. et al. (2020). “The Efficacy of Light Therapy in the Treatment of Seasonal Affective Disorder: A Meta-Analysis of Randomized Controlled Trials.” Psychotherapy and Psychosomatics, 89(1), 17-24.

The NHS, citing too little evidence, doesn’t usually provide light therapy, though it says many people find it helps. In some people with bipolar disorder, bright light can trigger hypomania, an unusually high, wired state. It may also not suit you if you have an eye condition or take something that increases light sensitivity, such as St John’s wort or some antibiotics.

CBT for SAD, and Why It May Last Longer

CBT for SAD works on two fronts. People schedule enjoyable activities through the dark months to counter the winter loss of interest, and learn to question gloomy thoughts about the season itself, such as dread of the dark. It ends with a plan for spotting early warning signs the next autumn.

A large head-to-head trial took place in Burlington, Vermont, where November days get about nine and a half hours of daylight. Kelly Rohan’s team randomly assigned 177 adults with winter depression to six weeks of either light therapy, starting at 30 minutes of 10,000 lux on waking, or CBT for SAD in 12 group sessions. Both groups improved about equally, with 47.6% of the CBT group and 47.2% of the light group in remission by interviewer ratings. Most participants were white women.

Rohan, K.J. et al. (2015). “Randomized Trial of Cognitive-Behavioral Therapy Versus Light Therapy for Seasonal Affective Disorder: Acute Outcomes.” American Journal of Psychiatry, 172(9), 862-869.

The team then followed the same people for two more winters. In the first, the groups did equally well. By the second, 27.3% of the CBT group had a recurrence of winter depression, against 45.6% of the light group. Light therapy usually has to be restarted each winter, and at the first follow-up only about a third of the light group said they were still using it as instructed. It’s one trial, and it needs repeating.

Rohan, K.J. et al. (2016). “Outcomes One and Two Winters Following Cognitive-Behavioral Therapy or Light Therapy for Seasonal Affective Disorder.” American Journal of Psychiatry, 173(3), 244-251.

You can borrow the approach today. Write down one thing you enjoy for each of the next seven days, ideally outdoors in daylight or with other people, and treat each as an appointment. NHS self-care advice for SAD adds daylight every day, regular exercise, time with friends and family, and steady sleep times. For the full therapy, ask your doctor; in England, adults can refer themselves to NHS Talking Therapies. Antidepressants are another option.

How to Choose and Use a SAD Lamp

Check with your doctor first if any of the cautions above apply. Then:

1. Choose a box rated at 10,000 lux at a stated distance, with UV filtered out. The NHS suggests one with a UKCA or CE mark.
2. Use it soon after you wake, for about 30 minutes. Morning sessions work better than evening ones, and late sessions can push your sleep later.
3. Sit at the distance the maker gives, with your eyes open. You don’t need to look into the light, so you can read or eat breakfast.
4. Use it every morning from autumn until your symptoms usually lift in spring.
5. If you get headaches or feel jittery, shorten the sessions and tell your doctor. If you feel unusually high or barely need sleep, stop and get medical advice quickly.

If a few weeks of daily sessions change nothing, or you feel worse, see your doctor.

SAD is diagnosed partly on its pattern, and memory is a poor record of last November. The mood check-in in Lamplit’s journal is free and takes three quick steps: how you feel, a word that fits (such as “drained”) and the area of life most affected. It saves even without a written entry. Do it daily through November, log daylight walks as Walking workouts, also free, then open the Mood Trend chart in the journal’s analytics. Lamplit can’t diagnose SAD, but you’ll have a record to show your doctor.

Do today’s mood check-in in your Lamplit journal. It’s free.