Seasonal affective disorder

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a type of depression that comes and goes with the seasons, typically starting in the late fall and early winter and going away during the spring and summer. Depressive episodes linked to the summer can occur, but are much less common than winter episodes of SAD.

The numbers

• Seasonal affective disorder is estimated to affect 10 million Americans. Psychology Today adds that “another 10 percent to 20 percent may have mild SAD” without saying 10 to 20 percent of what; we have not been able to establish the base, so treat that second figure as unusable rather than as a share of the population.
• SAD is four times more common in women than in men.
• The age of onset is estimated to be between 18 and 30.
• Some people experience symptoms severe enough to affect quality of life, and 6 percent require hospitalization.
• Many people with SAD report at least one close relative with a psychiatric disorder — most frequently severe depression (55 percent) or alcohol abuse (34 percent).

Watch: Learn about seasonal affective disorder (UPMC, YouTube) · How the seasons change your mood (UPMC)

In their words

When I Realized My Depression Was Seasonal

“It took me several years to realize how much sunlight and the seasons affect my mental health. My first episode of major depression began in late fall and eased in early spring, but at the time, that had no significance.” — Heidi Smith

Read the article (The Mighty)

Coping With S.A.D. Moments During Holidays With Seasonal Affective Disorder

“It's that time of year… when our days get shorter and our nights longer. And for some of us, that means our eyes are not twinkling and our dimples are not merry.” — Pamula Floyd

7 Ways I'm Preparing for Seasonal Affective Disorder This Year

“By the end of the winter I was definitely depressed. All I wanted to do was lay in bed and sleep all day and I had no motivation to do any of the activities that I usually enjoy.” — Adrienne Carrie Hubbard

The chemistry behind seasonal depression

How common SAD is depends on where you live, and the classic American study found rates rising with latitude: around 10 percent in New Hampshire against 1.4 percent in Florida. Read those numbers for what they are. They come from a questionnaire mailed to people picked from phone books, who scored themselves on how much their mood and sleep change with the seasons. That is a screening instrument, not a diagnosis, and screening-based rates run well above what a clinical interview finds. The latitude pattern is the finding; the percentages are an estimate of who would screen positive. SAD became a clinically diagnosed condition in the 1980s, when physician Norman Rosenthal noticed his own winter slumps after moving from South Africa and, with NIH colleagues, pioneered light exposure therapy.

A misaligned clock

Morning light is nature's alarm clock: special retinal cells signal the suprachiasmatic nucleus — the timekeeper of our circadian rhythms — which tells the pineal gland to stop secreting melatonin, the hormone that prepares your body for sleep. In winter, as light cues weaken, the body clock misaligns and melatonin secretion continues, tricking the body into thinking it's still night. Some people who are completely blind still retain these light-detecting cells — and can also experience SAD.

The light–melatonin pathway, in order

Light reaches the retina at the back of the eye. A signal travels along the optic nerve to the suprachiasmatic nucleus, a small cluster in the hypothalamus that keeps the body's daily clock. From there the signal reaches the pineal gland, which controls how much melatonin is released into the blood.

The direction is the thing to take from it. Light does not wake you by being bright. It reaches a clock, and the clock decides whether to switch the sleep hormone off. That is why the timing of light matters as much as the amount, and why a dark winter morning can leave the body still running its night-time chemistry at nine o'clock.

The March 2023 page illustrated this with a diagram. We have not republished it: the file we hold is a screen capture saved as “Screenshot 2019-12-11”, so it is someone else's diagram and we cannot establish whose. The sequence above is what it showed, and the words are ours.

The serotonin connection

Research also links SAD to depleted serotonin, the mood-regulating neurotransmitter — which helps explain winter cravings for carbohydrate-rich foods, known to spike these mood-enhancing chemicals. Brain scans show people with SAD have higher winter levels of the serotonin transporter protein (SERT); the more SERT, the less free serotonin, and the likelier the symptoms of depression.

How does treatment help?

Treatments for SAD include cognitive behavioral therapy, antidepressants, and light therapy; a doctor will recommend options based on the nature and severity of symptoms. The UK's National Institute for Health and Care Excellence recommends treating SAD the same way as other types of depression.

Things you can try yourself

• Get as much natural sunlight as possible — even a brief lunchtime walk helps
• Make your work and home environments as light and airy as possible, and sit near windows indoors
• Take plenty of regular exercise, particularly outdoors and in daylight
• Eat a healthy, balanced diet
• Where possible, avoid stressful situations and take steps to manage stress
• Talk to family and friends about SAD, so they understand how your mood changes in winter

Talking therapies and antidepressants

Cognitive behavioral therapy — individually, with a partner, in a group, or computer-based — works on the idea that the way we think and behave affects the way we feel. Counseling and psychodynamic psychotherapy are other talking options. SSRIs are the preferred antidepressant for SAD, thought to be most effective when started before winter symptoms appear and continued until spring; they can take 4 to 6 weeks for full effect.

Light therapy

Light therapy means sitting by a bright light box for around 30 minutes to an hour each morning, simulating the sunlight missing in winter — thought to reduce melatonin production and increase serotonin. Evidence on effectiveness is mixed, but some studies find it helps, particularly first thing in the morning, usually within a week or so. Side effects are rare and mild (agitation, headaches, sleep problems if used in the evening). Bright light may not suit people with light-sensitive eye conditions or on light-sensitizing medication — check with a doctor.

Celebrities who advocate

Rosie O'Donnell

“Like in The Wizard of Oz, the color goes out. That is what happens in depression. Everything gets gray.” On medication for depression: “It saved my life.”

Emma Chamberlain

“the fall/winter season challenges me mentally every year. every year, i'm convinced i'll be strong and not be affected by the changing of the season, but every year i get hit by a little bit of seasonal depression.”

Sources

1. National Institute of Mental Health — Seasonal affective disorder (the definition, restored from the older version; the newer page misattributed it)
2. Psychology Today — Seasonal affective disorder (the statistics)
3. Rosen LN et al. — Rosen LN et al. — Prevalence of seasonal affective disorder at four latitudes, Psychiatry Research 31(2):131–144, 1990 (the latitude figures; estimated from the mailed Seasonal Pattern Assessment Questionnaire, a screening instrument)
4. GB HealthWatch — The science behind seasonal affective disorder (the chemistry section)
5. NHS — Seasonal affective disorder (the treatment section, restored from the older version; the NHS treatment page now consolidates here)

Sources were last checked September 2026. Every source links to the exact document cited, never a homepage.