What Is Seasonal Affective Disorder? Signs, Causes and What Helps
Feeling flat as the days shorten is common. Seasonal affective disorder is more than that: a recurring pattern of depression. Here is how to tell the difference and what health bodies say can help.
When the clocks change and the evenings close in, plenty of people feel slower and gloomier. For some, though, the shift is not a passing mood. Seasonal affective disorder, or SAD, is a type of depression that comes back at the same time each year, usually in winter.
Here is what the NHS, the US National Institute of Mental Health (NIMH) and the American Psychiatric Association say about spotting it and treating it.
The short version
- SAD is a recurring seasonal pattern of depression, most often starting in late autumn or early winter and lifting in spring.
- The American Psychiatric Association says about 5% of US adults experience it, and it typically lasts about 40% of the year.
- Common signs include low mood, loss of interest, oversleeping, carbohydrate cravings and weight gain.
- Treatments include light therapy, cognitive behavioural therapy (CBT) and antidepressants. A doctor can help you choose.
What seasonal affective disorder actually is
The NHS describes SAD as "a type of depression that usually happens in the winter." In the American Psychiatric Association's diagnostic manual, it is classed as major depressive disorder with a seasonal pattern.
The NIMH says symptoms last about four to five months of the year. In the winter pattern, which is the more common one, they usually start in late autumn or early winter and fade in spring and summer. A summer pattern exists, but it is much less common. In the US, the American Psychiatric Association says January and February are typically the hardest months.
Signs to look for
The NHS lists low mood, loss of interest in usual activities, feelings of guilt, hopelessness or worthlessness, irritability, poor concentration, and increased tiredness and sleep. It also lists a bigger appetite.
The NIMH and the American Psychiatric Association point to a handful of features that set the winter pattern apart: oversleeping, overeating with carbohydrate cravings, weight gain and withdrawing from other people. The American Psychiatric Association adds that fatigue can persist even when someone is sleeping more than usual.
Some people also notice a burst of unusually high energy in early spring or summer, according to the NHS.
What causes it
The honest answer is that nobody knows exactly. The NHS says the cause is thought to be linked to reduced daylight in winter, which may affect the brain chemicals melatonin and serotonin and disrupt the body's sleep-wake cycle, known as the circadian rhythm.
That fits the pattern of who is affected. The NIMH says SAD is more common in people who live farther north, where winter days are shorter. Women are affected much more often than men, and it usually begins in young adulthood. The NIMH adds that it is more common in people with depression or bipolar II disorder and sometimes runs in families. The American Psychiatric Association puts the typical starting age between 18 and 30, though it can begin at any age.
How it differs from the winter blues
Feeling a bit sluggish in January does not mean you have SAD. For a diagnosis, the NIMH says depressive episodes must occur in a specific season for at least two consecutive years, and be more frequent in that season than at other times. The NHS likewise says a diagnosis is typically considered when symptoms appear at the same time of year for two years or longer.
A GP may ask about how your mood has changed over time and may use a questionnaire. The American Psychiatric Association also notes that SAD can be mistaken for other conditions, including an underactive thyroid, low blood sugar and viral infections such as infectious mononucleosis. That is one reason to get checked rather than guess.
What treatment looks like
The NHS says treatment can include antidepressants, talking therapies such as CBT and light therapy. Many people need treatment every winter to stop symptoms returning.
Light therapy. This means sitting in front of a bright light box, usually first thing in the morning. The NIMH describes a 10,000 lux box used for 30 to 45 minutes a day from autumn to spring, with UV light filtered out. The American Psychiatric Association says most people notice improvement within one to two weeks, and some start in early autumn to head symptoms off. The NHS notes light therapy is not usually offered on the NHS because the evidence of effectiveness is considered insufficient, though many people find it helpful. It advises speaking to a GP first, since a light box may not suit people with certain eye conditions or those taking medicines that increase light sensitivity. It also says to look for a lamp that is 10,000 lux, UV-free and carries a UKCA or CE mark.
CBT. The NIMH describes a version adapted for SAD, typically two group sessions a week for six weeks. In a long-term study cited by the NIMH, light therapy and CBT were about equally effective, but the effects of CBT seemed to last longer.
Medication. The NIMH says antidepressants usually take four to eight weeks to work, and the US Food and Drug Administration has approved extended-release bupropion to prevent seasonal episodes when it is taken daily from autumn through early spring. The American Psychiatric Association says SSRIs are the most commonly used class.
Vitamin D. It is a popular suggestion, but the NIMH says study results for vitamin D in winter-pattern SAD are mixed.
Everyday habits that support you
The American Psychiatric Association says spending more time in daylight, whether outdoors or by a window, may help, with the caution that UV exposure raises skin cancer risk. It also lists regular exercise, healthy eating, enough sleep and staying socially connected as ways to support wellbeing. The NHS lists regular exercise as a self-care step too. These habits are not a replacement for treatment if your symptoms are strong.
When to see a doctor
The NHS says to see a GP if you think you might have SAD, or if you have been diagnosed and treatment is not helping. In England, adults can refer themselves to NHS talking therapies without a GP referral. The NIMH says to talk to a health care provider or mental health specialist if you notice symptoms.
If you or someone you know is having thoughts of suicide, call or text 988 in the US, or chat at 988lifeline.org. In a life-threatening situation, call 911. The NHS directs people in a mental health crisis to urgent help services.
The pattern is worth noticing early. If every autumn brings the same heaviness, writing down when it starts and when it lifts gives you and your doctor something concrete to work with before the next winter arrives.
